Last year was the warmest since records began in the mid-1800s – and likely for many thousands of years before.
It was the first year in which average global temperatures at the surface exceeded 1.5C above pre-industrial levels in at least one global temperature dataset.
Here, Carbon Brief examines the latest data across the oceans, atmosphere, cryosphere and surface temperature of the planet.
Noteworthy findings from this 2023 review include…
- Global surface temperatures: It was the warmest year on record by a large margin – at between 1.34C and 1.54C above pre-industrial levels across different temperature datasets.
- Exceptional monthly temperatures: Global temperatures set a new record each month between June and December. September smashed the prior record for the month by a “gobsmacking” 0.5C.
- Warmest over land: It was the first year the global average land temperature was more than 2C above pre-industrial levels.
- Warmest over oceans: It was the first year that global average ocean surface temperatures exceeded 1C compared with pre-industrial levels.
- Ocean heat content: It was the warmest year on record for ocean heat content, which increased notably between 2022 and 2023.
- Regional warming: It was the warmest year on record in 77 countries – including China, Brazil, Austria, Bangladesh, Germany, Greece, Ireland, Japan, Mexico, the Netherlands, South Korea and Ukraine – and in areas where 2.3 billion people live.
- Unusual warmth: 2023 was much warmer than scientists estimated it would be at the start of the year and there remain open questions about what precise factors have driven the exceptional warmth. Even El Niño – the usual suspect behind record warm years – does not clearly explain 2023 temperatures.
- Comparison with climate models: Observations for 2023 are above the central estimate of climate model projections in the Intergovernmental Panel on Climate Change (IPCC) sixth assessment report, but well within the model range.
- Warming of the atmosphere: It was the warmest year in the lower troposphere – the lowest part of the atmosphere. The stratosphere – in the upper atmosphere – is cooling, due in part to heat trapped in the lower atmosphere by greenhouse gases.
- Sea level rise: Sea levels reached new record-highs, with notable acceleration over the past three decades.
- Shrinking glaciers and ice sheets: Cumulative ice loss from the world’s glaciers and from the Greenland ice sheet reached a new record high in 2023, contributing to sea level rise.
- Greenhouse gases: Concentrations reached record levels for CO2, methane and nitrous oxide.
- Sea ice extent: Arctic sea ice saw its sixth-lowest minimum extent on record, while Antarctic sea ice saw a new record low extent for almost the entire year, much of it by an exceptionally large margin.
- Looking ahead to 2024: Carbon Brief predicts that global average surface temperatures in 2024 are most likely to be slightly warmer than 2023 and set a new all-time record. However, large uncertainties remain given how exceptionally and unexpectedly warm 2023 was.
Use the links below to navigate between the article’s sections.
- Warmest year on record for the Earth’s surface
- Pushing up against the 1.5C target
- Highest ocean heat content on record
- A year of climate extremes
- Explaining 2023’s unusual heat
- Observations broadly in-line with climate model projections
- Record atmospheric temperatures
- Greenhouse gas concentrations reach new highs
- Accelerating sea level rise
- Shrinking glaciers and ice sheets
- Record-low Antarctic sea ice levels
- Looking ahead to 2024
Warmest year on record for the Earth’s surface
Global surface temperatures were exceptionally hot in 2023, exceeding the prior record set in 2016 by between 0.14C and 0.17C across different surface temperature datasets. It was unambiguously the warmest year since records began in the mid-1800s.
The figure below shows global surface temperature records from five different datasets: NASA; NOAA; the Met Office Hadley Centre/University of East Anglia’s (UEA) HadCRUT5; Berkeley Earth; and Copernicus ERA5.
Other surface temperature datasets not shown, including JRA-55, the AIRS satellite data and the Japanese Meteorological Agency, also show 2023 as the warmest year on record.
Annual global average surface temperatures over 1850-2023. Data from NASA GISTEMP, NOAA GlobalTemp, Hadley/UEA HadCRUT5, Berkeley Earth and Copernicus ERA5. Temperature records are aligned over the 1981-2010 period and use the average of NOAA, Berkeley and Hadley records to calculate warming relative to the pre-industrial baseline. Chart by Carbon Brief.
Global surface temperature records can be calculated back to 1850, though some groups such as NASA GISTEMP choose to start their records in 1880 when more data was available.
Prior to 1850, records exist for some specific regions, but are not sufficiently widespread to calculate global temperatures with high accuracy (though work is ongoing to identify and digitise additional records to extend these further back in time).
These longer surface temperature records are created by combining ship- and buoy-based measurements of ocean sea surface temperatures with temperature readings of the surface air temperature from weather stations on land. (Copernicus ERA5 and JRA-55 are an exception, as they use weather model-based reanalysis to combine lots of different data sources over time.)
Some differences between temperature records are apparent early in the record, particularly prior to 1900 when observations are more sparse and results are more sensitive to how different groups fill in the gaps between observations. However, there is excellent agreement between the different temperature records for the period since 1970, as shown in the figure below.
Annual global average surface temperatures as in the prior chart, but showing the period from 1970-2023. Chart by Carbon Brief.
Global temperatures in 2023 clearly stand out as much warmer than anything that has come before. This can be seen in the figure below from Berkeley Earth. Each shaded curve represents the annual average temperature for that year. The further that curve is to the right, the warmer it was.
The width of each year’s curve reflects the uncertainty in the annual temperature values (caused by factors such as changes in measurement techniques and the fact that some parts of the world have fewer measurement locations than others).
The year 2023 was the warmest on record for both the world’s land and ocean regions.
It was also the first year where global average land temperatures exceeded 2C and the first year in which global ocean temperatures exceeded 1C relative to pre-industrial levels.
The figure below shows land (red) and ocean (blue) temperatures along with their respective confidence intervals, relative to pre-industrial levels, in the Berkeley Earth surface temperature record.
Global land regions – where the global human population lives – has been warming around 70% faster than the oceans – and 40% faster than the global average in the years since 1970.
While 2023 as a whole has been exceptionally warm, it started off a bit cooler, with the first few months of the year failing to set any new records. However, from June onward each month was warmer than the same month in any prior year since records began. September was particularly “gobsmacking”, shattering the prior September record by a full 0.5C.
The figure below shows each month of 2023 in black, compared to all prior years since 1850. Each year is coloured based on the decade in which it occurred, with the clear warming over time visible as well as the exceptional margin by which 2023 exceeded past years between July and December.
Pushing up against the 1.5C target
In the 2015 Paris Agreement, the world agreed to work to limit global temperatures to well-below 2C and to pursue efforts to “limit the temperature increase to 1.5C above pre-industrial levels”.
While the exceedance of these climate targets was not specifically defined in the agreement, it has since been widely interpreted (for example, by the IPCC) as a 20-year average period.
Crucially, the limits refer to long-term warming, rather than an individual year that includes the short-term influence of natural fluctuations in the climate, such as El Niño.
However, a single year exceeding 1.5C still represents a grim milestone, a sign that the world is quickly approaching the target. And, in the Berkeley Earth dataset, 2023 was the first year above 1.5C.
It came in a hair’s width below 1.5C in the Copernicus and Hadley datasets, at 1.48C and 1.46C, respectively, and was lower on NOAA and NASA datasets as shown in the table below.
| Temperature record | 2023 temperatures relative to preindustrial |
|---|---|
| NOAA GlobalTemp | 1.34C |
| NASA GISTEMP | 1.39C* |
| Hadley/UAE HadCRUT5 | 1.46C |
| Copernicus/ECMWF | 1.48C |
| Berkeley Earth | 1.54C |
Global temperature anomalies for 2023 relative to preindustrial temperatures (1850-1899). *Note that GISTEMP uses a 1880-1899 baseline as it does not cover the 1850-1879 period.
As noted earlier, these datasets are nearly identical over the past 50 years. Differences in warming relative to pre-industrial levels emerge earlier in the record, particularly prior to 1900 when observations are more sparse and the choice of how to fill in the gaps between observations has a large impact on the resulting temperature estimate.
The figure below shows how different temperature records look if each is calculated relative to its own pre-industrial baseline, rather than using an average pre-industrial baseline as shown in the prior section. Focusing on warming since pre-industrial – rather than more recent warming – magnifies differences between groups, with the variation in warming across groups largely due to the most uncertain early part of the record.
Highest ocean heat content on record
Last year was the warmest on record for the heat content of the world’s oceans. Ocean heat content (OHC) has increased by around 473 zettajoules – a billion trillion joules – since the 1940s. The heat increase in 2023 alone compared to 2021 – about 15 zettajoules – is around 25 times as much as the total energy produced by all human activities on Earth in 2021 (the latest year in which global primary energy statistics are available).
Human-emitted greenhouse gases trap extra heat in the atmosphere. While some of this warms the Earth’s surface, the vast majority – around of 93% – goes into the oceans. About two-thirds of this accumulates in the top 700 metres, but some also ends up in the deep oceans.
The figure below shows annual OHC estimates between 1950 and present for both the upper 700 metres (light blue shading) and 700-2,000 metres (dark blue) of the ocean.
Annual global ocean heat content (in zettajoules – billion trillion joules, or 10^21 joules) for the 0-700 metre and 700-2,000 metre layers. Data from Cheng et al. (2024). Chart by Carbon Brief.
In many ways, OHC represents a much better measure of climate change than global average surface temperatures. It is where most of the extra heat ends up and is much less variable on a year-to-year basis than surface temperatures. It shows a distinct acceleration after 1991, matching the increased rate of greenhouse gas emissions and other radiative forcing elements over the past few decades.
This year saw a substantial update to the OHC dataset provided by the Institute for Atmospheric Physics (IAP) that Carbon Brief features in its State of the Climate reports. The transition from version 3 to version 4 introduced a new quality control system to detect and remove spurious measurements across different instrument types.
As the figure below highlights, this results in a notable increase in OHC over the past decade (red lines and shading) relative to the prior version of the dataset (black lines).
A year of climate extremes
While media coverage of 2023 temperatures has largely focused on the global average, there have been many different regions of the planet experiencing climate extremes.
The figure below shows global temperature anomalies in 2023 across the world, with red areas warmer than the baseline period (1951-80) used by Berkeley Earth and blue areas experiencing cooler temperatures.
In 2023, 77 countries saw their warmest year on record, including: Afghanistan, Albania, Antigua and Barbuda, Argentina, Austria, Azerbaijan, Bangladesh, Bhutan, Bolivia, Bosnia and Herzegovina, Brazil, Bulgaria, Cape Verde, Cameroon, China, Comoros, Costa Rica, Croatia, Cuba, Czechia, Dominica, Dominican Republic, Ecuador, El Salvador, Federated States of Micronesia, Gambia, Germany, Greece, Grenada, Guatemala, Guinea, Guyana, Haiti, Honduras, Hungary, Ireland, Ivory Coast, Jamaica, Japan, Kazakhstan, Kiribati, Kosovo, Kyrgyzstan, Liechtenstein, Macedonia, Mexico, Moldova, Montenegro, Morocco, Myanmar, Netherlands, Nicaragua, Nigeria, North Korea, Oman, Panama, Paraguay, Peru, Republic of the Congo, Romania, Saint Kitts and Nevis, Saint Lucia, Saint Vincent and the Grenadines, San Marino, Senegal, Serbia, Slovakia, Slovenia, South Korea, Tajikistan, The Bahamas, Trinidad and Tobago, Turkmenistan, Ukraine, Uzbekistan, Venezuela and Yemen.
Approximately 2.3 billion people, or around 29% of Earth’s population, live in places that observed their locally warmest year during 2023.
The figure below highlights regions of the planet that experienced their top-five warmest (red shading) or coldest (blue) temperatures on record in 2023. Overall, around 17% of the planet set a new record, including 23% of the land and 14% of the ocean. No location on the planet experienced record cold temperatures (or even top-5 record cold temperatures) for the year as a whole.
Explaining 2023’s unusual heat
Scientists did not expect 2023 to be all that exceptional at the start of the year. As Carbon Brief reported at the start of 2023, four different groups provided temperature predictions for the year prior to any data being collected – the UK Met Office, NASA’s Dr Gavin Schmidt, Berkeley Earth and Carbon Brief’s own estimate.
Temperature predictions for 2023 from the UK Met Office, NASA’s Dr Gavin Schmidt, Berkeley Earth and Carbon Brief relative to pre-industrial (1880-99) temperatures. Chart by Carbon Brief.
As Carbon Brief noted in January 2023:
“La Niña conditions are expected to persist for at least the first three months of 2023. Because there is a lag of a few months between when El Niño or La Niña conditions peak in the tropical Pacific and their impact on global temperatures, these La Niña conditions will likely have a lingering cooling influence on 2023 temperatures.”
Carbon Brief estimated that 2023 was “very likely to be between the third and ninth warmest year on record, with a best estimate of being the fifth warmest on record – similar to 2022”, and suggest that if an El Niño develops in latter half of 2023 it would make it likely that 2024 will set a new record.
This estimate, alongside all the other groups predicting 2023 temperatures, was wrong. Not only did 2023 turn out to be the warmest year on record, but it fell well outside the confidence intervals of any of the estimates. And while there are a number of factors that researchers have proposed to explain 2023’s exceptional warmth, scientists still lack a clear explanation for why global temperatures were so unexpectedly high.
Over the longer-term, human emissions of CO2 and other greenhouse gases alongside planet-cooling aerosols are the main driver of global temperatures. Global temperatures have risen by approximately 1.3C since pre-industrial times as a result of human activity. However, on top of long-term warming, global temperatures vary year to year by up to 0.2C.
These variations are primarily driven by El Niño and La Niña events that redistribute heat between the atmosphere and oceans. However, other factors such as volcanic eruptions, the 11-year solar cycle and changes in short-lived climate forcers can influence year-to-year temperature changes.
The figure below, created by Dr Robert Rohde at Berkeley Earth, explores some of the main drivers of temperature change over the past decade.
These include continued accumulation of greenhouse gases, the evolution of El Niña and La Niña, and the 11-year solar cycle. It also includes two new factors that emerged during the decade: the 2022 eruption of the Hunga Tonga volcano and the 2020 phase-out of sulphur in marine fuels. Both of these are estimated to have relatively modest effects at present – less than 0.05C each – but with large scientific uncertainties.
However, both the Tonga eruption and the phase-out of sulphur in marine fuel are problematic explanations of extreme temperatures in 2023.
There is still a vigorous debate in the scientific literature about whether the eruption cooled or warmed the planet based on estimates of both sulphur dioxide and water vapour in the atmosphere, with some papers arguing for warming and others for cooling. Some modelling suggests that the largest impacts of the eruption would be in winter months, which does not match the timing of extreme summer temperatures experienced in 2023.
Similarly, the phase-out of sulphur in marine fuels occurred in 2020. If it had a large climate impact, it would show up in 2021 and 2022 rather than suddenly affecting the record in 2023. While it definitely has had a climate impact – alongside the broader reduction in aerosol emissions over the past three decades – the timing suggests that its likely not the primary driver of 2023 extremes.
Even El Niño – the usual suspect behind record warm years – does not clearly explain 2023 temperatures. Historically global temperatures have lagged around three months behind El Niño conditions in the tropical Pacific; for example, El Niño developed quite similarly in 1997, 2015 and 2023. But it was the following year – 1998 and 2016 – that saw record high temperatures.
The figure below shows the El Niño (red shading) and La Niña (blue) conditions over the past 40 years (collectively referred to as the El Niño-Southern Oscillation, or “ENSO”). While not unprecedented, the extended La Niña conditions since the latter part of 2020 have extended for an unusually long period of time.
Carbon Brief has used this historical relationship between ENSO conditions and temperature to effectively remove the effects of El Niño and La Niña events from global temperatures, as shown in the figure below.
However, this approach – which has worked well for prior years – indicates that there would be almost no effect of El Niño on temperatures in 2023. This is because the lingering global temperature impact of La Niña conditions on the first half of the year would approximately cancel out the influence of El Niño on the second half. This model would suggest that the current El Niño event would primarily affect 2024 temperatures, analogous to what occurred in 1998 and 2016.
Annual global average surface temperatures from Berkeley Earth, as well as Carbon Brief’s estimate of global temperatures with the effect of El Niño and La Niña (ENSO) events removed using the Foster and Rahmstorf (2011) approach. Figures are shown relative to a 1981-2010 baseline. Chart by Carbon Brief.
It is possible that this El Niño event is behaving differently and that the rapid switch from a rare and extended triple-dip La Niña event from late 2020 to the start of this year into strong El Niño conditions is resulting in a more rapid global temperature response.
But this remains speculative at this point and researchers are just starting to disentangle the causes of the unexpected extreme global heat the world experienced in 2023.
Observations broadly in-line with climate model projections
Climate models provide physics-based estimates of future warming given different assumptions about future emissions, greenhouse gas concentrations and other climate-influencing factors.
Here, Carbon Brief examines a collection of climate models – known as CMIP6 – used in the 2021 science report of the IPCC’s sixth assessment. In CMIP6, model estimates of temperatures prior to 2015 are a “hindcast” using known past climate influences, while temperatures projected after 2015 are a “forecast” based on an estimate of how things might change.
Using the CMIP6 ensemble is a bit more challenging than past generations of models because a subset of models have unrealistically high climate sensitivity and poorly reproduce historical observations. Rather than simply average all the models – as had been done in prior assessments – the IPCC used an approach that effectively weights models by their performance. This means the models align better with the range of climate sensitivity derived from multiple different lines of evidence.
The figure below shows the range of individual CMIP6 model projections since 1950, as well as future projections through to 2100 under the middle-of-the-road SSP2-4.5 emissions scenario.
The black line shows the average of 22 different models whose transient climate response (TCR) falls within the IPCC’s “likely” range (which results in temperature projections nearly identical to the IPCC assessed warming). The grey area shows the 95% (two standard deviation) range of the TCR-screened model projections. Observational temperatures are plotted on top of the climate model data, with individual observational records represented by coloured lines.
Annual global average surface temperatures from CMIP6 models and observations between 1950 and 2030 (through to 2023 for observations). Models use the SSP2-4.5 scenario after 2015. They are screened to only include those models with a transient climate response (TCR) in-line with the IPCC’s “likely” range as discussed in Hausfather et al (2022). Anomalies plotted with respect to a 1981-2010 baseline. Chart by Carbon Brief.
Using the TCR-screened subset, the findings show that 2023 temperatures are above the model average, but still well within the range of climate model projections. While some individual months have approached the upper end of the model range, the year as a whole is less anomalous.
The figure below shows the observed warming since pre-industrial (1850-99) in the five different observational datasets compared with climate model projections. The box plot below shows the 25th to 75th percentile of models and observations with a solid box, while the whiskers show 1.5 times the interquartile range.
Temperatures in 2023, relative to pre-industrial, were in the upper quartile (>75th percentile) of climate models assessed. However, this is not unexpected, as models do not have internal variability such as El Niño or La Niña events that occur at the same time as they do in the real world. (Scientists would expect observations to be on the high end of the model range during El Niño years and on the low end in La Niña years even if climate models were perfectly accurate.)
Finally, the figure below shows how observations compare to the full ensemble of 37 CMIP6 models, with no screening for transient climate response. Here, observations are generally below the model average over the past two decades and are roughly equal to the model average in 2023.
Annual global average surface temperatures from CMIP6 models and observations between 1950 and 2030 (through 2023 for observations). Models use the SSP2-4.5 scenario after 2015. Anomalies plotted with respect to a 1981-2010 baseline. Chart by Carbon Brief.
Record atmospheric temperatures
In addition to surface measurements over the world’s land and oceans, satellite microwave sounding units have been providing estimates of temperatures at various layers of the atmosphere since 1979.
The lowest layer they estimate – the lower troposphere – reflects temperatures a few kilometres above the surface and shows a pattern of warming similar – though not identical – to surface temperature changes. The records produced by Remote Sensing Systems (RSS) and the University of Alabama, Huntsville (UAH) both show 2023 as the warmest year on record in the lower troposphere. The chart below shows the two records – RSS in red and UAH in blue – for the lower troposphere (TLT).
Global average lower-troposphere temperatures from RSS version 4 (red) and UAH version 6 (blue) for the period from 1979-2023, relative to a 1981-2010 baseline. Chart by Carbon Brief.
The lower troposphere tends to be influenced more strongly by El Niño and La Niña events than the surface. Therefore, satellite records show correspondingly larger warming or cooling spikes during these events. This is why, for example, 1998 shows up as one of the warmest years in satellites, but not in surface records.
The two lower-tropospheric temperature records show large differences after the early 2000s. RSS shows an overall rate of warming quite similar to surface temperature records, while UAH shows considerably slower warming in recent years than has been observed on the surface. Both have seen large adjustments in recent years that have warmed RSS and cooled UAH compared to prior versions of each record.
Overall, there is more agreement with RSS to other records that include satellite data (such as reanalysis products ERA5 and JRA-55, as well as the shorter AIRS satellite-based surface temperature record), while the UAH record is a bit of an outlier compared to the others.
In addition to a temperature record of the lower troposphere, RSS and UAH also provide measurements of the lower stratosphere – a region of the upper atmosphere around 18km above the surface. The figure below shows lower stratospheric temperature (TLS) records for both RSS (red) and UAH (blue) from 1979 through 2023.
Global average lower stratospheric temperatures from RSS version 4 (red) and UAH version 6 (blue) for the period from 1979-2023, relative to a 1981-2010 baseline. Chart by Carbon Brief.
The stratosphere has been cooling for the past few decades in a clear fingerprint of human greenhouse gases, which warm the lower part of the atmosphere by trapping heat while cooling the upper atmosphere as less heat escapes. If other factors – such as changing solar output – were causing climate change, both the stratosphere and troposphere would be warming.
Greenhouse gas concentrations reach new highs
Greenhouse gas concentrations reached a new high in 2023, driven by human emissions from fossil fuels, land use and agriculture.
Three greenhouse gases – CO2, methane (CH4) and nitrous oxide (N2O) – are responsible for the bulk of additional heat trapped by human activities. CO2 is by far the largest factor, accounting for roughly 42% of the increase in global surface temperatures since the pre-industrial era (1850-1900).
Methane accounts for 28%, while nitrous oxide accounts for around 5%. The remaining 25% comes from other factors including carbon monoxide, black carbon and halocarbons, such as CFCs.
Human emissions of greenhouse gases have increased atmospheric concentrations of CO2, methane and nitrous oxide to their highest levels in at least a few million years – if not longer.
The figure below shows concentrations of these greenhouse gases – in parts per million (ppm) for CO2 (blue line) and parts per billion (ppb) for methane (orange) and nitrous oxide (red) – from the early 1980s through to October 2023 for CO2 and September 2023 for CH4 and N2O (the most recent data currently available).
Global concentrations of CO2, methane (CH4) and nitrous oxide (N2O). Based on data from NOAA’s Earth Systems Research Laboratory. Note that the y-axes do not start at zero. Chart by Carbon Brief.
Methane concentrations, in particular, have seen a sharp rise over the past decade after a plateau in the 2000s. This appears to be driven by both increased emissions from agriculture and fossil fuels, in roughly equal measure. Thawing Arctic permafrost and other sources of methane in high-latitude regions are growing, but emissions above a latitude of 60 degrees north are only around 4% of the total global methane emissions.
Accelerating sea level rise
Modern-day sea levels have risen to a new high, due to a combination of melting land ice (such as glaciers and ice sheets), the thermal expansion of water as it warms and changes in land water storage.
In recent years, there have been larger contributions to sea level rise from melting ice sheets and glaciers, as warmer temperatures accelerate ice sheet losses in Greenland and Antarctica.
Since the early 1990s, the increase in global sea level has been estimated using altimeter data from satellites. Earlier global sea levels have been reconstructed from a network of global tide gauge measurements. This allows researchers to estimate how sea level has changed since the late 1800s.
The chart below shows five different modern sea level rise datasets (coloured lines), along with satellite altimeter measurements from NASA satellites as assessed by the University of Colorado (in black) after 1993. (As sea level rise data has not yet been released for the whole year, the 2023 value is estimated based on data through October.)
Global average sea level rise reconstructed from tide gauge data between 1880 and 2023 from Frederikse et al 2020, Dangendorf et al 2019, Hay et al 2015, Church and White 2011, and Palmer et al 2021. Satellite altimeter data from 1993 (black) to present is taken from the University of Colorado. Chart by Carbon Brief.
Sea levels have risen by over 0.2 metres (200mm) since 1900. While sea level rise estimates mostly agree in recent decades, larger divergences are evident before 1980. There is also evidence of accelerating sea level rise over the post-1993 period when high-quality satellite altimetry data is available. (See Carbon Brief’s explainer on how climate change is accelerating sea level rise.)
Shrinking glaciers and ice sheets
A portion of this sea level rise is being driven by melting glaciers on land. Scientists measure the mass of glaciers around the world using a variety of remote-sensing techniques, as well as through GRACE measurements of the Earth’s gravitational field. The balance between snow falling on a glacier and ice loss through melting and the breaking off – or “calving” – of icebergs determines if glaciers grow or shrink over time.
The World Glacier Monitoring Service is an international consortium that tracks 164 different glaciers in 19 different regions around the world. The figure below shows the change in global average glacier mass from 1950 through to the end of 2022 (2023 values are not yet available). Note that glacier melt is reported in metres of water equivalent, which is a measure of how much mass has been lost on average.
Global average glacier melt over the 1950-2022 period from the World Glacier Monitoring Service, in metres of water equivalent. Carbon Brief.
Greenland ice sheets have become a larger contributor to sea level rise in recent years due to accelerating loss of mass. The year 2023 was the 27th in a row where Greenland lost ice overall, with 196Gt of ice lost over the 12 months from September 2022 to August 2023. Greenland last saw an annual net gain of ice in 1996.
The figure below shows the cumulative mass balance change – that is, the net ice loss – from Greenland between 1970 and October 2021. The different coloured lines indicate estimates from different studies. The authors find that Greenland has lost over 6tn metric tonnes of ice over the past 50 years – more than 700 tonnes lost per person for every person on the planet.
Cumulative ice loss from Greenland in billion metric tonnes (gigatonnes) between 1970 and 2023 from Mankoff et al 2021, updated through December 2023. Chart by Carbon Brief.
Record-low Antarctic sea ice levels
Arctic sea ice was at the low end of the historical (1979-2010) range for most of 2023, but did not set any new all-time low records apart from a few individual days in February and March. The summer minimum extent – the lowest recorded level for the year – was the sixth-lowest since records began in the late 1970s.
Antarctic sea ice, on the other hand, saw new record low levels for virtually the entire year – except for periods in April, November and December of the year.
Antarctic sea ice was particularly low between June and November, shattering prior records by a substantial margin. While long-term trends in Antarctic sea ice have been ambiguous in the past (unlike in the Arctic where there is a consistent long-term decline), there is increasing evidence that human-driven warming is starting to drive significant loss of sea ice in the region.
The figure below shows both Arctic (red line) and Antarctic (blue line) sea ice extent for each day of the year, along with how it compares to the historical range (corresponding shading).
Arctic and Antarctic daily sea ice extent from the US National Snow and Ice Data Center. The bold lines show daily 2023 values, the shaded area indicates the two standard deviation range in historical values between 1979 and 2010. The dotted black lines show the record lows for each pole. Chart by Carbon Brief.
Looking ahead to 2024
The unusual global temperatures experienced in 2023 makes it more challenging to predict what 2024 might have in store.
If history is any guide here, the year after the development of an El Niño event tends to be considerably warmer than the year in which it develops. For example, strong El Niño events developed over the latter half of both 1997 and 2015 and peaked early the following year, and 1998 and 2016 both set new records by a large margin.
However, 2023 was so exceptionally warm that it suggests that this El Niño might be behaving differently, with global surface temperatures responding more rapidly than in the past. If this is the case, 2024 would not necessarily follow the pattern of past El Niño events and is less likely to be substantially warmer than 2023.
There have been four published predictions – from the UK Met Office, NASA’s Dr Gavin Schmidt, Berkeley Earth and Carbon Brief (in this article) – of what temperatures might look like in 2024.
The figure below shows the four different 2024 predictions compared to the average of six different temperature records (NASA, NOAA, Hadley, Berkeley, Copernicus, and the Japanese JRA-55 reanalysis) used by the World Meteorological Organization (WMO). These have been “normalised” to show 2024 warming relative to 2023 in the WMO dataset. This is to remove any differences in predictions due to divergences in the baselines used by different temperature records.
Carbon Brief’s prediction of likely 2024 temperatures is based on a statistical model using the year, the average temperature of the past year, and projections of El Niño/La Niña conditions over the first three months to predict the temperatures of the year.
Temperature projections for 2024 from the UK Met Office, NASA’s Dr Gavin Schmidt, Berkeley Earth, and Carbon Brief, relative to pre-industrial (1880-99) temperatures and compared to the historical average of six different datasets produced by the WMO. Chart by Carbon Brief.
The Met Office, Dr Schmidt, Berkeley Earth and Carbon Brief estimates all have 2024 as more likely than not to be warmer than 2023 – but only by a small margin. In all estimates it is close to a coin flip which will end up as the warmer year.
Against a 1880-99 pre-industrial baseline, the central estimate of all four forecasts is just below 1.5C of warming, with ranges suggesting that temperatures could top 1.5C next year.
However, the poor performance by all of these groups in accurately predicting 2023 temperatures mean these should be treated with some caution. Until scientists have a clearer understanding of the drivers of the unusual warmth the world experienced in 2023, it will not be possible to fully predict how temperatures will evolve in 2024 as the current El Niño event peaks and fades away.
Ultimately, what matters for the climate is not the leaderboard of individual years. Rather, it is the long-term upward trend in global temperatures driven by human emissions of greenhouse gases. Until the world reduces emissions down to net-zero, the planet will continue to warm.
As the chart below highlights, if the warming trend over the past 40 years continues, average surface temperatures are likely to pass 1.5C in the early 2030s and 2C by around 2060.
The post State of the Climate: 2023 smashes records for surface temperature and ocean heat appeared first on Carbon Brief.
State of the Climate: 2023 smashes records for surface temperature and ocean heat
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Cropped 8 October 2025: US government shutdown; EU loses green space; Migratory species extinction threat
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Key developments
Forest fund delays and cuts
TFFF BEHIND SCHEDULE: Brazil’s flagship forest fund, the Tropical Forest Forever Facility (TFFF), is “running behind schedule as officials deliberate on how to structure the complex financial vehicle” in time for COP30, Bloomberg reported. The “ambitious” fund aims to raise $125bn to help countries protect rainforests “using investment returns from high-yielding fixed-income assets”, it explained. However, the outlet reported that investor events have either not been held or cancelled, while officials are still mulling “possible structures” for the fund.
CUTS DEEP: Environmentalists fear that “sweeping spending cuts for forest protection” by Argentina’s “pro-business libertarian” president, Javier Milei, could endanger the country’s forests, Climate Home News reported. The impacts of these cuts are “already becoming evident”, contributing to deforestation – particularly in the northern Gran Chaco region, environmentalists told the outlet. According to Argentine government data, the country lost about 254,000 hectares of forest nationwide in 2024. Milei – who has said he wants to withdraw Argentina from the Paris Agreement – faces a “crucial midterm election” in October that could make environmental deregulation even easier, the outlet wrote.
BANKING ON THE AMAZON: A new report found that 298 banks around the world “channelled $138.5bn” to companies developing new fossil-fuel projects in Latin America and the Caribbean, Mongabay reported. The experts behind the study told the outlet: “Some major banks have adopted policies to protect the Amazon, but these have had little impact, as they do not apply to corporate-level financing for oil and gas companies operating in the Amazon.” Mongabay approached every bank, but only JPMorgan Chase responded, declining to comment.
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‘Green to grey’
‘600 FOOTBALL PITCHES’: Europe is losing “green space…at the rate of 600 football pitches a day”, according to a new, cross-border investigation by the “Green to Grey Project”, the Guardian reported. The outlet – part of the Arena for Journalism in Europe collaboration of journalists and scientists behind the project – added that Turkey accounted for more than a fifth of the total loss in Europe. While nature “accounts for the majority of the losses”, the research showed that the EU is also rapidly building on agricultural land, “with grave consequences for the continent’s food security and health”, it continued.
‘TWICE AS HIGH’: Conducted by 40 journalists and scientists from 11 countries, the investigation found that the “natural area” lost to construction in the EU was “twice as high as official estimates”, Le Monde reported. Despite Brussels setting a 2011 target to “reduce the EU’s yearly land take” to 800km2 – “more than 100,000 football fields” – the EU is “artificialising more than 1,000km2 of land per year”, it added.
KEY DRIVERS: While the “main drivers of land loss across Europe” are housing and road-building, Arena for Journalism in Europe found many instances of construction “that serve only a minority or that are not built based on public need”, such as luxury tourism sites. Between 2018 to 2023, “an area the size of Cyprus” in nature and cropland was lost to construction, they added. Researchers who “scrutinised millions of pixels in search of lost natural areas” found that Finland’s tourism boom is “encroaching on the last remaining sanctuaries” in Lapland, another Le Monde story reported.
News and views
‘INTRACTABLE’ OFFSETS: A new review paper found that the failure of carbon offsets to cut emissions is “not due to a few bad apples”, but “down to deep-seated systemic problems that incremental change will not solve”, the Guardian wrote. Study co-author Dr Stephen Lezak told the outlet: “We have assessed 25 years of evidence and almost everything up until this point has failed.” The worst of these “intractable problems” were with “issuing additional credits” for “non-additional”, “impermanent” and double-counted projects, the Guardian noted.
INSTITUTIONALISING AGROECOLOGY: The Cuban government issued a national decree providing a “more explicit legal framework” for the implementation of agroecological principles across the country, according to a release from the Caribbean Agroecology Institute. The decree also announced a new national fund for promoting agroecology. Yamilé Lamothe Crespo, the country’s deputy director of science, innovation and agriculture, “emphasised that agroecology is a model capable of responding to the global climate crisis”, teleSUR reported.
ZERO PROGRESS TO ZERO HUNGER: The world has “made no improvement” towards achieving the “zero hunger” Sustainable Development Goal since it was set in 2015, according to a new report from the UN Food and Agriculture Organization. The report said that “ongoing geopolitical tensions and weather-related disruptions” have contributed to “continued instability in global food markets”. Separately, a new report from the Energy and Climate Intelligence Unit thinktank estimated that a “year’s worth of bread” has been lost in the UK since 2020 due to extreme weather impacting wheat harvests, the Guardian reported.
MEATLESS MEDIA: More than 96% of analysed climate news stories across 11 (primarily US-based) outlets “made no mention of meat or livestock production as a cause of climate change”, according to analysis by Sentient Media. Sentient, a not-for-profit news organisation in the US, looked at 940 stories to assess the reported causes of greenhouse gas emissions. Around half of the stories included mention of fossil fuels, it said. Covering the report, the Guardian wrote: “The data reveals a media environment that obscures a key driver of the climate crisis.”
FRAUGHT PATH: One-fifth of migratory species “face extinction from climate change”, according to a new report by the UN’s migratory species convention, covered by Carbon Copy. The “warning” comes as climate change and extreme weather are “altering their ranges [and] shrinking habitats”, the Mail & Guardian wrote. Oceanographic Magazine noted that the North Atlantic right whale is “forced to make migratory detours into dangerous pockets of the ocean” due to warming seas. Down to Earth reported that the range of Asian elephants is “shifting east” in “response to anthropogenic land-use and climate change”.
GOODBYE, GOODALL: Dr Jane Goodall, the groundbreaking English primatologist, died at the age of 91 last week. BBC News noted that Goodall “revolutionised our understanding” of chimpanzees, our “closest primate cousins. The outlet added that she “never wavered in her mission to help the animals to which she dedicated her life”. CNBC News reported that Goodall followed a vegan diet due to factory farming and the “damage done to the environment by meat production”. She also “encouraged” others to follow her example, the outlet said.
Spotlight
What the US government shutdown means for food, forests and climate
This week, Carbon Brief explains the US government shutdown – now in its second week – and its implications for food, forests, public lands and climate change.
The US federal government shut down at 12:01 eastern daylight time on 1 October, as Congress failed to agree on a bill to keep funding the government and its services.
This is the 11th time that the government has shut down in such a fashion; previous shutdowns have lasted anywhere from a few hours to longer than a month.
As a result of the shutdown, 750,000 federal employees have been furloughed, or placed on unpaid leave. Others, whose work has been deemed “essential”, are working without pay.
(A law passed during a shutdown in US president Donald Trump’s first term guarantees back pay and benefit accrual for furloughed employees. However, the White House has argued that the law does not necessarily guarantee these benefits.)
Some agencies have seen close to 90% of their employees furloughed.
With a reopening date uncertain, Carbon Brief explored what the shutdown means for food, forests and climate.
Food and farming
According to the agency’s “lapse of funding” plan, the US Department of Agriculture (USDA) planned to furlough about half of its employees for the duration of the shutdown.
Among the activities put on hold during the funding lapse are the disbursement of disaster-assistance payments for farmers impacted by extreme weather events. The Farm Service Agency, which oversees these payments, will also not process any new loans during the shutdown, such as those that provide assistance to farmers during the harvest.
The Natural Resources Conservation Service, an arm of the USDA with a mission to help private landowners “restore, enhance and protect forestland resources”, has seen more than 95% of its staff furloughed, effectively halting all conservation efforts within the agency.
Certain animal-health programmes – such as the one addressing the highly pathogenic avian influenza outbreak – will continue, but others will shutter for the duration of the funding lapse. Long-term research on animal and plant diseases will also cease.
Forests and fires
The US Forest Service falls under the purview of the USDA. Employees responsible for “responding [to] and preparing for wildland fires” will continue to work during the shutdown; however, “hazardous fuels treatments” – such as prescribed burns or pruning to reduce fuel loads – will be reduced under the agency’s plan. Furthermore, state grants for fire preparedness and forest management “may be delayed”.
Work on forest restoration projects may potentially continue “on a case-by-case basis”, the plan said.
The Bureau of Land Management (BLM), a subdivision of the Department of the Interior, will furlough around 43% of its employees, according to its contingency plan. Staff dedicated to fire management will continue to work while “carryover balances” are available, but the number of staff working will be reduced once these funds are exhausted.
Climate change and research
Across the federal government, most research activities are being put on hold, including conference travel and the issuing of new grants.
Grant recipients may continue carrying out research “to the extent that doing so will not require federal staff” and while funds are available, according to the National Science Foundation’s operational plan. This does not include researchers at federal agencies, such as the Environmental Protection Agency, US Geological Survey and the National Oceanic and Atmospheric Administration (NOAA).
The funding-lapse plan set out by the Department of Commerce said that NOAA will continue its prediction and forecasting activities, as well as maintain “critical and mission-related” programmes related to research satellites. However, “most research activities” will cease.
Similarly, NASA’s shutdown plan indicates continuing support for satellite operations, but a pause on research activities – except for those “aligned with presidential priorities”.
Watch, read, listen
MORAINE DILEMMA: A new PBS documentary walked through ancient Inca paths in the Andes to understand how modern communities are confronting the loss of Peru’s glaciers.
SUBSIDISING ‘EXPLOITATION’: A DeSmog investigation revealed how farmers convicted of “exploiting migrant workers” continue to claim “millions in taxpayer-funded subsidies”.
GROUND TRUTHING: A podcast from the Hindu looked back at 20 years of India’s Forest Rights Act, meant to “address historic injustices” towards the country’s Indigenous communities.
DEEP DIVE MANUAL: Mongabay journalists shared how they investigated Brazil’s shark-meat purchases that were subsequently served in schools, prisons and hospitals.
New science
- The frequency of “economically disastrous” wildfires increased sharply after 2015, with the highest disaster risk in “affluent, populated areas” in the Mediterranean and temperate regions | Science
- A “strictly protected” forest in Tuscany had maximum summertime temperatures that were, on average, nearly 2C cooler than those of nearby productive forests over 2013-23 | Agricultural and Forest Meteorology
- Between 2010 and 2020, the water consumed by global crop-growing increased by 9%, putting “additional pressure on limited water resources” | Nature Food
In the diary
- 9-15 October: 2025 World Conservation Congress of the International Union for Conservation of Nature (IUCN) | Abu Dhabi, United Arab Emirates
- 10-17 October: World Food Forum 2025 | Rome
- 16 October: World Food Day | Global
- 25 October: Ivory Coast presidential election
Cropped is researched and written by Dr Giuliana Viglione, Aruna Chandrasekhar, Daisy Dunne, Orla Dwyer and Yanine Quiroz. Please send tips and feedback to cropped@carbonbrief.org
The post Cropped 8 October 2025: US government shutdown; EU loses green space; Migratory species extinction threat appeared first on Carbon Brief.
From canola farmers in Canada to car owners in India, biofuels have become the subject of everyday debate across the world.
Liquid biofuels feature heavily in the climate plans of many countries, as governments prioritise domestic energy security amid geopolitical challenges, while looking to meet their climate targets and bolster farm incomes.
Despite a rapid shift towards electrified transportation, biofuels continue to play a leading role in efforts to reduce road-transport emissions, as they work well with many existing car engines.
At the same time, biofuels are expected to play an important role in decarbonising sectors where emissions are particularly challenging to mitigate, such as shipping, trucking and aviation.
Heated debates continue around using food sources as fuel in the face of record hunger levels, given competing demands for land and crops.
Despite these arguments, biofuels are seeing heightened demand bolstered by a strong policy push, particularly in developing countries.
They are expected to feature heavily on the COP30 agenda this year as a key feature of the host Brazil’s “bioeconomy”.
Below, Carbon Brief unpacks what biofuels are, their key benefits and criticisms, plus how they are being used to meet climate targets.
- What are biofuels?
- What are the most common biofuels being used today?
- What are the main arguments for biofuels?
- What are some of the main criticisms of biofuels?
- How are countries using biofuels to meet their climate targets?
- How could climate change impact biofuel production?
What are biofuels?
Bioenergy refers to all energy derived from biomass, a term used to describe non-fossil material from biological sources. Biofuels, in turn, are liquid fuels that are produced from biomass.
These sources are wide-ranging, but commonly include food crops, vegetable oils, animal fats, algae and municipal or agricultural waste, along with synthetic derivatives from these products.
Glossary
Biomass
Non-fossil material of biological origin
Biofuel
Fuels produced directly or indirectly from biomass
Feedstock
Types of biomass used as sources for biofuels, such as crops, grasses, agricultural and forestry residues, wastes and microbial biomass
Bioenergy
All energy derived from biofuels
Bioethanol
A biofuel used as a petrol substitute, produced from the fermentation of biomass from plants like corn, sugarcane and wheat
Biodiesel
A biofuel used as a diesel substitute, derived from vegetable oils or animal fats through a process called transesterification
The different types of biomass are referred to as “feedstocks”. They are converted to fuel through one or more processes, such as fermentation or treating them with high temperatures or hydrogen.
Biofuels are frequently blended with petroleum products in an effort to reduce emissions and reliance on fossil-fuel imports.
Experiments to test whether vegetable oils could run in combustion engines began in the early 1900s. In a 1912 paper, Rudolf Diesel – the inventor of the diesel engine – presciently noted that these oils “make it certain that motorpower can still be produced from the heat of the sun…even when all our natural stores of solid and liquid fuels are exhausted”.
An extract from Rudolf Diesel’s 1912 paper, published in the Proceedings of the Institution of Mechanical Engineers, outlining the importance biofuels could assume in the future. Credit: Proceedings of the Institution of Mechanical Engineers (1912)
Biofuels are divided into four “generations”, based on the technologies and feedstocks used to synthesise them.
| Type of biofuel | Source |
| First-generation | Food crops (eg, sugarcane, corn, wheat, rice) |
| Second-generation | Non-edible crops and materials (eg, straw, grasses, used vegetable oil, forest residues, waste) |
| Third-generation | Aquatic materials (eg, algae) |
| Fourth-generation | Genetically modified algae, bacteria and yeast, as well as electrofuels, synthetic fuels and e-fuels |
First-generation biofuels
The first – and earliest – generation of biofuels comes from edible crops, such as corn, sugarcane, soya bean and oil palm. Large-scale commercial production of these fuels began in the 1970s in Brazil and the US from sugarcane and corn, respectively.
Bioethanol, for instance, is drawn from the fermentation of sugars in corn, sugarcane and rice. Biodiesel is derived from vegetable oils – such as palm, canola or soya bean oil – or animal fats, through a process called transesterification, which makes them less viscous and more suitable as fuels.
Because they are derived directly from food crops, experts and campaigners have expressed concerns over the impacts of first-generation biofuels on forests, food security and the environment, as well as indirect land-use change impacts. (See: What are some of the main criticisms of biofuels?)
Several studies have found that the land-use emissions of first-generation biofuels are severely underestimated, but other experts tell Carbon Brief that this depends on how and where the crops are grown, processed and transported.
According to Dr Angelo Gurgel, principal research scientist at the Massachusetts Institute of Technology (MIT) Center for Sustainability Science and Strategy, the “big image that biofuels are bad” is not always accurate. Gurgel explains:
“Some biofuels can be better than others, varying from place to place and feedstock to feedstock. It depends on where you produce them, how much farmers can increase yields, how effectively a country’s regulations help avoid land-use change and how closely it is connected to international markets.
“Some options may be very, very good in terms of reducing emissions and other options probably will be very bad.”
Second-generation biofuels
Second-generation biofuels are extracted from biomass that is not meant for human consumption.
Feedstocks for these biofuels are incredibly varied. They include agricultural waste, such as straw and corn stalks, grasses, forest residues left over from wood processing, used vegetable oil and solid waste. They can also be made from energy crops grown specifically to serve as biofuels, such as jatropha, switchgrass or pongamia.
Derived from “waste” or grown on “marginal” land, second-generation biofuels were developed in the early 2000s. These fuels aimed to overcome the food security and land-use issues tied to their predecessors, while increasing the amount of fuel drawn out from biomass, compared to first-generation feedstocks.
These feedstocks are either heated to yield oil or “syngas” and then cooled, or treated with enzymes, microorganisms or other chemicals to break down the tough cellulose walls of plants. They can be challenging to process and present significant logistical and land-use challenges.
Third-generation biofuels
Third-generation biofuels are primarily derived from aquatic organic material, particularly algae and seaweed. While the US Department of Energy began its aquatic species programme in 1978 to research the production of biodiesel from algae, algal biofuel research saw a “sudden surge” in the 1990s and “became the darling” of renewable energy innovation in the early 21st century, says Mongabay.
Because algae grows faster than terrestrial plants, is high in lipid (fatty organic) content and does not compete with terrestrial crops for land use, many scientists and industry professionals consider third-generation biofuels an improvement over their predecessors.
However, high energy, water and nutrient needs, high production costs and technical challenges are key obstacles to the large-scale production of algae-based biofuels. Since the early 2010s, many companies, including Shell, Chevron, BP and ExxonMobil, have abandoned or cut funding to their algal biofuel development programmes.
Fourth-generation biofuels
Genetically modified algae, bacteria and yeast engineered for higher yields serve as the feedstock for fourth-generation biofuels. These fuels have been developed more recently – from the early 2010s onwards – and are an area of ongoing research and development.
Some of these organisms are engineered to directly or artificially photosynthesise solar energy and carbon dioxide (CO2) into fuel; these are called solar biofuels.
Others – called electrofuels, synthetic fuels or e-fuels – are produced when CO2 captured from biomass is combined with hydrogen and converted into hydrocarbons through other processes, typically using electricity generated from renewable sources.
Fourth-generation biofuels are technology- and CO2-intensive and expensive to produce. They also run up against public perception and legal limitations on genetically modified organisms, as well as concerns around biosafety and health.
What are the most common biofuels being used today?
Bioethanol is the most commonly used liquid biofuel in the world, followed by biodiesel.
In 2024, global liquid biofuel production increased by 8% year-on-year, with the US (37%) and Brazil (22%) accounting for the largest overall share of production, according to the 2025 Statistical Review of World Energy from the Energy Institute.
Other countries that saw a notable increase in production between 2023-24 were Sweden (62%), Canada (39%), China (30%), India (26%) and Argentina (24%).
Bioethanol is the most commonly used biofuel in the world, with a consumption rate of 1.1m barrels of oil equivalent per day in 2024, according to the report. This is closely followed by biodiesel, at 1m barrels of oil equivalent per day.
In 2024, the US, Brazil and the EU accounted for nearly three-quarters of all biofuels consumed globally. However, while India’s biofuel demand grew by 38%, demand for biofuels in the EU fell by 11% in 2024, according to the review, echoing outlooks that show that middle-income countries are driving biofuel growth.
The chart below shows how biofuel production and consumption have changed since 2000, and how they are projected to change through 2034.
What are the main arguments for biofuels?
From lowered oil imports and emissions through to boosting farm livelihoods, countries that have boosted biofuels programmes cite several benefits in biofuels’ favour.
‘Renewable’ energy and lowered emissions
Biofuels are often described as “renewable” fuels, since crops can be grown over and over again.
In order to achieve this, crops for biofuels must be continuously replanted and harvested to meet energy demand. Growing crops – particularly in the monoculture plantations typically used for growing feedstocks – can require high use of fossil fuels, in the form of machinery and fertiliser. Furthermore, in the case of wood as a feedstock, regrowth can take decades.
While some biofuels offer significant emissions reductions, others, such as palm biodiesel, generate similar or sometimes higher emissions as fossil fuels when burned. However, ancillary emissions for biofuels are much smaller than for oil and gas operations.
One of the main cited benefits of biofuels is that plants capture CO2 from the atmosphere as they grow, potentially serving to mitigate emissions. However, several lifecycle-assessment studies have questioned just how much plants can offset emissions. These studies come up with varying estimates based on feedstock types, geography, production routes and methodology.
This divergence is echoed in the UN Intergovernmental Panel on Climate Change’s (IPCC) Sixth Assessment Report (AR6), which points to “contrasting conclusions” even when similar bioenergy systems and conditions are analysed.
Per the report, there is “medium agreement” on the emissions-reduction potential of second-generation biofuels derived from wastes and residues by 2050.
At the same time, the IPCC adds that “technical land availability does not imply that dedicated biomass production for bioenergy…is the most effective use of this land for mitigation”.
It also warns that larger-scale biofuel use “generally translates into higher risk for negative outcomes for greenhouse gas emissions, biodiversity, food security and a range of other sustainability criteria”.
Along with the IPCC, many other groups and experts – including the UK’s Climate Change Commission – have called for a “biomass hierarchy”, pointing to a limited amount of sustainable bioenergy resources available and how best to prioritise their use.
Use in hard-to-abate sectors
In many countries, such as the US and UK, biofuels are part of a standard grade of diesel and petrol (gasoline) available at most fuel pumps.
Biofuels have also been the leading measure for decarbonising road transport in emerging economies, where electric vehicle systems were not as developed as in many western nations.
According to the International Energy Agency (IEA), most new biofuel demand is coming from these countries, including Brazil, India and Indonesia.
Biofuels are also one of the key options being explored to decarbonise the emissions-heavy, but “hard-to-abate”, sectors of aviation and shipping.
The AR6 report notes that the “faster-than-anticipated adoption of electromobility” has “partially shifted the debate” from using biofuels primarily in land transport towards using them in shipping and aviation.
At the same time, experts question how this can be done sustainably, given the limited availability of advanced biofuels and the rising demand for them.
Government reports – such as those released by the EU Commission – recognise that, in some circumstances, so-called sustainable aviation fuels (SAFs) could produce just as many emissions as fossil fuels when burned in order to power planes.
However, SAFs do generally – although not always – have a lower overall “lifecycle” carbon footprint than petroleum-based jet fuel. This is due to the CO2 absorbed when growing plants for biofuels, or emissions that are avoided by diverting waste products to be used as fuels.
Unlike the road sector, where “electrification is mature…aviation and shipping cannot be electrified so easily”, says Cian Delaney, fuels policy officer at the Brussels-based advocacy group Transport & Environment (T&E).
According to a 2025 T&E briefing, the 2030 demand for biofuels from global shipping alone could require an area the “size of Germany”. Delaney tells Carbon Brief:
“In aviation in particular, where you still need some space to transition, you still need a certain amount of biofuels. But these biofuels should be advanced and waste biofuels derived from true waste and residues, and they are available in truly limited amounts, which is why, in parallel, we need to upscale the production of e-fuels [synthetic fuels derived from green hydrogen] for aviation.”
In February this year, more than 65 environmental organisations from countries including the US, Indonesia and the Netherlands wrote to the International Maritime Organization, urging its 176 member states to “exclude biofuels from the industry’s energy mix”.
The organisations cited the “devastating impacts on climate, communities, forests and other ecosystems” from biofuels, cautioning that fuels such as virgin palm oil are often “fraud[ulently]” mislabelled as used cooking oil – a key feedstock for SAF.
Meanwhile, the AR6 report has “medium confidence” that heavy-duty trucks can be decarbonised through a combination of batteries and hydrogen or biofuels. And despite growing interest in the use of biofuels for aviation, it says, “demand and production volumes remain negligible compared to conventional fossil aviation fuels”.
Energy security and reducing import dependence
In many countries, such as India and Indonesia, biofuels are seen as a part of a suite of measures to increase energy security and lessen dependence on fossil-fuel imports from other countries. This imperative received increasing emphasis after the Covid-19 pandemic and Russia’s war on Ukraine.
In developing countries, the “main motivation” behind biofuel policy is to find an alternative to excessive dependence on imported fossil fuels that are a “major drain” on foreign exchanges and subject to volatility and price shocks, says Prof Nandula Raghuram, professor of biotechnology at the Guru Gobind Singh University in New Delhi.
Raghuram, who formerly chaired the International Nitrogen Initiative, tells Carbon Brief that, in order for developing countries to “earn those precious dollars to finance our petroleum imports”, they have to export “valuable primary commodities”, such as grain and vegetables, at the cost of nutritional self-reliance. He adds:
“And so we have to see the biofuel approach as not so much a proactive strategy, but as a sort of reactive strategy to use whatever domestic capacity we have to produce whatever domestic fuel, including biofuels, to reduce that much burden on the exchequer for imports.”
Boost to agriculture
Many governments also see biofuels as an alternative income stream for farmers and a means to revitalise rural economies.
An increasing demand for biofuels could, for example, offer farmers higher returns on their crops, attract industry and services to agrarian areas and help diversify farm incomes.
In 2023, a report by the International Labour Organization (ILO) and the International Renewable Energy Agency (IRENA) estimated that the liquid biofuel industry employed approximately 2.8 million people worldwide.
The bulk of these jobs were in Latin America and Asia, where farming is more labour-intensive and relies on informal and seasonal employment. Brazil’s biofuel sector alone employed nearly one million people in 2023, according to the report.
Meanwhile, North America and Europe accounted for only 12% and 6% of biofuel jobs in 2023, respectively, according to the report.
The chart below shows the number of jobs in the biofuel sector in the top 10 biofuel-producing countries.
Delaney points out that biofuel-related jobs account for less than 1% of all jobs in the EU, adding that the “most-consumed biofuel feedstocks” in the bloc are vegetable oils that are imported from countries such as Brazil and Indonesia. (See: How are countries using biofuels to meet their climate targets?)
He tells Carbon Brief:
“Despite strong biofuels mandates in the EU, the sector didn’t create as many jobs in the end for EU farmers, but, instead, benefited the big fuel suppliers and industry players.”
What are some of the main criticisms of biofuels?
Despite their widespread use and increasing adoption, experts recognise that biofuels “may also carry significant risks” and cause impacts that can undermine their sustainability, if not managed carefully.
Production emissions, land-use change and deforestation
The different chemical processes involved in making biofuels require varying amounts of energy and, therefore, the associated emissions depend on how “clean” a producer country’s energy mix is.
At the same time, growing biofuel crops often relies on emissions-intensive fertilisers and pesticides to keep yields high and consistent. (See Carbon Brief’s detailed explainer on what the world’s reliance on fertilisers means for climate change.)
Biofuel production processes, such as fermentation, also release CO2 and other greenhouse gases, including methane and nitrous oxide.
MIT’s Gurgel tells Carbon Brief that it is “relatively straightforward” to measure these direct emissions from biofuel production.
However, given how different countries account for deforestation, tracking direct land-use change emissions related to biofuel production is slightly more challenging – although still possible, Gurgel says. These emissions can come from clearing forests or converting other land specifically for growing energy crops.
For example, in many tropical forest countries, native rainforests and peatland have been cleared to grow oil palm for biodiesel or sugarcane for bioethanol.
According to one 2011 study by the Centre for International Forestry Research and World Agroforestry (CIFOR-ICRAF), it could take more than 200 years to reverse the carbon emissions caused by clearing peatland to grow palm oil.
Gurgel tells Carbon Brief:
“What is really very hard – I would say impossible – to measure are the indirect impacts of biofuels on land.”
Indirect land-use change occurs when a piece of land used to grow food crops is used instead for biofuels. This can, in turn, require deforestation somewhere else to produce the same amount of crops for food as the original piece of land.
Indirect land-use change can mean a loss of natural ecosystems, with “significant implications for greenhouse gas emissions and land degradation”, according to a 2024 review paper.
Gurgel explains:
“If you provoke a chain of reactions in the market, that can lead to expansion of cropland in another region of the world and then this can push the agricultural frontier further and cause some deforestation…It’s quite hard to know exactly what’s going to happen and those things are interactions in the market that are impossible to measure.”
The “best that scientists can do” to determine if such a “biofuel shock” could indeed cause land-use change in a forest or grassland elsewhere “is try to project those emissions using models, or do very careful statistical work that will never be complete”, he adds.
Delaney, from Transport and Environment, contends that there is enough scientific research to “show that indirect land-use change is real” and to quantify the expansion of “certain food and feedstocks into high-carbon stock” areas, such as forests.
While this is “not easy” to do, he points to the European Commission’s indirect land-use change directive, the accompanying methodology and its scientific teams who study agricultural expansion rates. Delaney continues:
“What we all agree with at this point is that indirect land-use change exists, that it’s a problem, that certain feedstocks like palm and soya are particularly problematic from this perspective and that it is an issue that we need to tackle and capture in the best possible way.
“You cannot just be vague and descriptive without having proper figures behind it – and I think that’s something that at least the EU have tried and that they continue trying to implement. And I hope that, at the global level as well, this will be more recognised.”
Impacts on food, biodiversity and water security
Biofuel-boosting policies have been subjected to intense scrutiny during periods of global food-price spikes in 2008, 2011 and 2013.
Following the spikes, critics attributed increasing biofuel production as a major factor in the near-doubling of cereal prices. Studies have shown that they played a more “modest” role in some of these spikes and a more substantial one in others.
Severalexperts have linked food-price spikes to protests in north Africa and the Middle-East, including the Arab Spring.
In more recent years, the “food vs fuel debate” has come back to the fore since the start of the war in Ukraine in 2022.
This was in part due to the world’s reliance on Ukraine and Russia’s food and energy systems – particularly some of the most food-insecure countries, who had to contend with record-high food prices that peaked in March 2022, but still persist. The war also saw heightened calls for the US and EU to overturn biofuel-boosting policies to free up land to increase domestic food production and bring down food prices.
In developing countries, such as India, the use of cereals and oils to make biofuels while large sections of the population still lack access to adequate nutrition has attracted criticism from experts.
While first-generation biofuels rely on fertilisers to guarantee consistently high yields, second-generation biofuels could directly compete with feed for livestock or their return to soil as nutrients.
According to a 2013 report by the panel of scientists that advises the UN Committee on World Food Security (CFS):
“All crops compete for the same land or water, labour, capital, inputs and investment, and there are no current magic non-food crops that can ensure more harmonious biofuel production on marginal lands.”
This competition, along with clearing forests and other ecosystems for cropland, has consequences not just for emissions, but also for biodiversity, water and nutrients.
According to one 2021 review paper, local species richness and abundance were 37% and 49% lower, respectively, in places where first-generation biofuel crops were being grown than in places with primary vegetation. Additionally, it found that soya, wheat, maize and palm oil had the “worst effects” on local biodiversity, with Asia and central and South America being the most-impacted regions.
Biofuels’ impact on water resources, similarly, is highly crop- and location-specific.
For instance, growing a “thirsty” crop such as sugarcane in Brazil could have minimal impacts on local water resources, due to the region’s abundant rainfall. But in drought-prone India, experts have estimated that a litre of sugarcane ethanol requires more than 2,500 litres of water to produce and relies entirely on irrigation. Research has also found that nearly half of China’s maize crop requires irrigation to grow.
According to agricultural economist Dr Shweta Saini, meeting India’s 2025-26 biofuels target will require 275m tonnes of sugarcane, 6m tonnes of maize and 5.5m tonnes of rice. According to one 2020 study cited by Bloomberg columnist David Fickling, increasing sugarcane production to meet India’s biofuel targets “could consume an additional 348bn cubic metres of water…around twice what is used by every city” in the country.
Prof Raghuram tells Carbon Brief:
“Water resources are drying up everywhere in the country and by incentivising, through policy, a water-guzzling industry like this, we are inviting a sustainability crisis.”
‘Feedstock crunch’
Another concern surrounding biofuels is that there may not be enough supply to go around to meet rising demand. The IEA described the potential shortfall as a “feedstock supply crunch” in a 2022 report.
Fuels derived from the most commonly used waste and residues, in particular, could be approaching supply limits, the IEA warns, as these fuels satisfy both sustainability and feedstock policy objectives in the US and EU.
Consumption of vegetable oil for biofuel production is expected to soar by 46% over 2022-27, the report says. Meanwhile, the world is estimated to “nearly exhaust 100% of supplies” of used cooking oil and animal fats within the decade.
For the world to stay on a net-zero trajectory, “a more than three times production increase” would be required, the report adds. It warns that if the limited availability of second-generation feedstocks continues unchanged, “the potential for biofuels to contribute to global decarbonisation efforts could be undermined”.
The chart below shows the biofuel demand share of global crop production from 2022-27.
How are countries using biofuels to meet their climate targets?
Broadly, biofuel policies are divided into two categories.
Technology “push” policies focus on the research and development of new technologies and include measures such as research funding, pilot plants and government support for commercialising nascent technologies.
Meanwhile, market “pull” policies drive demand for existing and emerging biofuels through measures such as “biofuel blending mandates” – where countries prescribe a certain percentage of biofuel with fossil fuels – and tax breaks for producers and vehicle owners.
US
The US Renewable Fuel Standard (RFS) is the world’s largest existing biofuel programme. Its mandates are keenly watched and contested by the country’s farm and petroleum lobbies.
Under RFS, the US Environmental Protection Agency sets out minimum levels of biofuels that must be blended into the US’s transport, heating and jet fuel supplies.
Under the policy, oil refiners can either blend mandated volumes of biofuels into the nation’s fuel supply or buy credits – called Renewable Identification Numbers (RINS) – from those that do.
While the programme sets out emissions reduction targets, the environmental impacts of cropland expansion and monoculture driven by the policy have been cause for concern by experts.
According to one 2022 study, the RFS programme increased US fertiliser use by 3-8% each year between 2008-16 and caused enough domestic emissions from land-use change that the carbon intensity of corn ethanol was “no less than that of gasoline and likely at least 24% higher”. Additionally, the programme’s impacts on biodiversity have not yet been fully assessed.
In June 2025, the Trump administration announced plans to expand the biofuel mandate to a “record 24.02bn gallons” next year – an 8% increase from its 2025 target – while seeking to discourage imported biofuels.
EU
In the EU, policymakers have promoted biofuels since 2003 to reduce emissions in the transport system. As part of the EU’s Renewable Energy Directive (RED), biofuels have been explicitly linked to emissions targets.
Under the current iteration of RED (REDIII) – revised as part of the EU’s Fit for 55 package – EU countries are required to either achieve a share of 29% of renewable energy in transport or to reduce the emissions intensity of transport fuels by 14.5%. Additionally, it sets out a sub-target for “advanced biofuels” of 5.5% and excludes the use of food and feed-based biofuels in aviation and shipping.
In 2015, the European Commission acknowledged that the indirect land-use change emissions of first-generation biofuels could “fully negate” any emission savings by biofuels. The commission capped the use of first-generation biofuels in each member country at 7% of all energy used in transport by 2020, but did not announce plans to phase them out.
As of 2021, nearly 60% of all biofuels used in the EU were still made from food and feed crops, according to analysis by Oxfam. While the latest RED legislation continues to push for the use of advanced and waste biofuels, campaigners warn that a lack of clear definitions could increase the risk of “loopholes” and fraud, exacerbated by increased demand.
T&E’s Delaney tells Carbon Brief:
“You’re putting a lot of pressure on the land – you might require a lot of pesticides and irrigation – and there is not even enough land in Europe for this. How can you make sure true sustainability safeguards are in place so that you’re not actually driving additional demand for land in [biodiverse countries such as] Brazil?”
Brazil
Brazil has the world’s oldest biofuels mandate, dating back to the 1970s, established in a bid to insulate the country from expensive oil imports.
In 2017, Brazil announced a state policy called RenovaBio that set out national carbon intensity reduction targets for transport, decided biofuel mandates and created an open market for biofuel decarbonisation carbon reduction credits called CBIO.
In October 2024, Brazil enacted a “Fuels of the Future” law that replaced RenovaBio, with president Lula declaring that “Brazil will lead the world’s largest energy revolution”. The law aims to boost biofuel and sustainable aviation fuel (SAF) use, increasing biodiesel blending mandates by 1% every year starting in 2025 until it reaches 20% by March 2030.
Biofuels now account for 22% of the energy that fuels transport in Brazil and its ethanol market is “second in size only” to the US.
In June this year, Brazil announced that the country was increasing its biofuel blending mandates from 1 August in a bid to make the country “gasoline self-sufficient for the first time in 15 years”, reported Reuters.
Indonesia
As the world’s biggest palm oil producer, Indonesia has continued to raise its biodiesel blending mandates to meet its domestic energy needs.
The country first introduced mandatory biodiesel blending in 2008, at 2.5%. The mandate is currently at 40% in 2025 and, starting next year, could go up to 50% with an eventual goal of 100%.
While Indonesia’s president Prabowo Subianto has stated that implementing 50% blending could save the country $20bn in reduced diesel imports, the move would need an estimated 2.3m hectares of land, including protected forests, resulting in the “country’s largest-ever deforestation project”, according to Mongabay.
It could also compete with palm oil meant for domestic and international food markets, impacting already soaring prices and signalling the “end of cheap palm oil”.
India
India has quickly joined the ranks of major biofuel producers, due to high-level political support, policies and a diversity of feedstocks. In 2023, India launched the Global Biofuels Alliance as one of its key priorities of its G20 presidency.
Biofuel mandates are outlined in the country’s National Policy on Biofuels, first published in 2009 and subsequently amended in 2018 and 2022. In 2022, India achieved its 10% ethanol blending target ahead of schedule and is pursuing a 20% blending target by 2025, as well as a 5% biodiesel blending target by 2030.
India’s rapid biofuel push, however, has been criticised by food security experts as hunger levels rise, for its impact on endemic rainforests and, most recently, by vehicle owners for the impact of blended fuel on car engines.
Prof Raghuram says:
“From a sheer governance angle and sustainability angle, there are a lot of compromises being made to somehow push this whole thing. Even the land available in India is shrinking, as various reforms and dilution of environmental safeguards in the last 10 years have made it relatively easier to convert farm and forest land for non-agricultural purposes.”
China
China developed its first biofuel policies over 20 years ago and is one of the world’s biggest biofuel producers.
In 2017, China announced a new mandate expanding the use of fuel including bioethanol from 11 trial provinces to the entire country by 2020. However, Reuters and South China Morning Post reported that this was suspended in 2020. Only 15 provinces still maintain biofuel mandates, according to the US Department of Agriculture, which notes that a “lack of meaningful support for domestic biofuel consumption while aggressively promoting electric vehicles indicates a strategic choice to pursue transportation decarbonisation through electrification rather than liquid biofuels”.
At the same time, biofuel production in China grew by 30% in 2024, according to the Energy Institute’s Statistical Review.
While most of China’s biofuel production is grain-based, tax incentives for ethanol production have been gradually phased out and alternative biofuels have been incentivised, according to the IEA. China is currently piloting a scheme to increase biodiesel consumption at home, even as it exports biodiesel and used cooking oil to the EU and US.
How could climate change impact biofuel production?
Despite the well-documented impacts of climate change-induced extreme weather on land, agriculture and forests, there is currently little scientific literature examining how continued warming will impact global biofuel production.
One 2020 study found that bioethanol availability globally could drop – by 23% under a “very high emissions scenario” and by 4.3% under a “low emissions” scenario by 2060 – “if climate change risk is not adequately mitigated” and corn continues to be the dominant feedstock.
The study “encourages” changing out corn for switchgrass as a key source of bioethanol.
Another 2021 study examining the viability of China’s planned biofuel targets estimated that energy crop yields in China in the 2050s will decrease significantly compared to the 2010s, due to the impacts of climate change.
It found that climate change is expected to have a “substantial impact” on the land available for biofuel production in the 2050s, under both scenarios used in the study.
Gurgel, from MIT, tells Carbon Brief that it is “very hard to take into account how much climate change will damage bio-energy production” at this point, given the uncertainty of what emissions pathway the world will follow.
While most climate models “do a very good job” at forecasting average temperature change in the future, they do an “average job” at projecting rainfall change, or how many extreme weather events countries will see in the future, he says.
This is important because many biofuel crops, such as sugarcane and palm oil, are water-intensive and thrive in regions with abundant rainfall, but yields may fail in drier parts of the world that could see more drought.
Given this “cascade of uncertainties”, he continues, “we don’t have a clear picture of how bad the future [of agriculture] will be – we just know it will be more challenging than today”.
Delaney, meanwhile, asks whether investing in biofuels, which will be impacted by climate change, is a “good investment” for the long term. He tells Carbon Brief:
“I think these are the questions that we need to ask ourselves when we see – not just in India, but Indonesia, Brazil, everywhere around the world right now – this growing appetite for biofuels. Can we really keep the promises that we made at the end of the day?”
The post Q&A: How countries are using biofuels to meet their climate targets appeared first on Carbon Brief.
Q&A: How countries are using biofuels to meet their climate targets
The first-ever international conference on the contentious topic of “overshoot” was held last week in a palace in the small town of Laxenburg in Austria.
The three-day conference brought together nearly 200 researchers and legal experts to discuss future temperature pathways where the Paris Agreement’s “aspirational” target to limit global warming to 1.5C is met “from above, rather than below”.
Overshoot pathways are those which exceed the 1.5C limit – before being brought back down again through techniques that remove carbon from the atmosphere.
The conference explored both the feasibility of overshoot pathways and the legal frameworks that could help deliver them.
Researchers also discussed the potential consequences of a potential rise – and then fall – of global temperatures on climate action, society and the Earth’s climate systems.
Speaking during a plenary session, Prof Joeri Rogelj, a professor of climate science and policy at Imperial College London, said that “moving into a world where we exceed 1.5C and have to manage overshoot” was an exercise in “managing failure”.
He said that it was “essential” that this failure was acknowledged, explaining that this would help set out the need to “minimise and manage” the situation and clarify the implications for “near-term action” and “long-term [temperature] reversal”.
Below, Carbon Brief draws together some of the key talking points, new research and discussions that emerged from the event.
- Defining overshoot
- Mitigation ambition and 1.5C viability
- Carbon removal
- Impacts of overshoot
- Adaptation
- Legal implications and loss and damage
- Communication challenges and next steps
Defining overshoot
The study of temperature overshoot has grown in recent years as the prospects of limiting global temperature rise to 1.5C have dwindled.
Conference organiser Dr Carl-Friedrich Schleussner – a senior research scholar at the International Institute for Applied Systems Analysis (IIASA) – explained the event was designed to bring together different research communities working on a “new field of science”.
He told Carbon Brief:
“If we look at [overshoot] in isolation, we may miss important parts of the bigger picture. That’s why we also set out the conference with very broad themes and a very interdisciplinary approach.”
The conference was split between eight conference streams: mitigation ambition; carbon dioxide removal (CDR); Earth system responses; climate impacts; tipping points; adaptation; loss and damage; and legal implications.
There was also a focus on how to communicate the concept of overshoot.
In simple English, “overshoot” means to go past or beyond a limit. But, in climate science, the term implies both a failure to meet a target – as well as subsequent action to correct that failure.
Today, the term is most often deployed to describe future temperature trajectories that exceed the Paris Agreement’s 1.5C limit – and then come back down.
(In the Intergovernmental Panel on Climate Change’s (IPCC’s) fifth assessment cycle, completed in 2014, the term was used to describe a potential rise and then fall of CO2 concentrations above levels recommended to meet long-term climate goals. A recent “conceptual” review of overshoot noted this was because, at the time, CO2 concentrations were the key metric used to contextualise emissions reductions).
The plot below provides an illustration of three overshoot pathways. The most pronounced pathway sees global temperatures rise significantly above the 1.5C limit – before eventually falling back down again as carbon dioxide is pulled from the atmosphere at scale.
In the second and third pathways, global temperature rise breaches the limit by a smaller margin, before either falling enough just to stabilise around 1.5C, or dropping more dramatically due to larger-scale carbon removals.
In an opening address to delegates, Prof Jim Skea, who is the current chair of the IPCC, acknowledged the scientific interpretation of overshoot was not intuitive to non-experts.
“The IPCC has mainly used two words in relation to overshoot – “exceeding” and “limiting”. To a lay person, these can sound like opposites. Yet we know that a single emissions pathway can both exceed 1.5C in the near term and limit warming to 1.5C in the long term.”
Noting that different research communities were using the term differently, Skea urged researchers to be precise with terminology and stick to the IPCC’s definition of overshoot:
“We should give some thought to communication and keep this as simple as possible. When I look at texts, I hear more poetic words like “surpassing” and “breaching”. I would urge you to keep the range of terms as small as possible and make sure that we’re absolutely using them consistently.”
In the glossary for its latest assessment cycle, AR6, the IPCC defines “overshoot” pathways as follows:
IIASA’s Schleussner stressed that not all pathways that go beyond 1.5C qualify as overshoot pathways:
“The most important understanding is that overshoot is not any pathway that exceeds 1.5C. An overshoot pathway is specific to this being a period of exceedance. It is going to come back down below 1.5C.”
Mitigation ambition and 1.5C viability
Perhaps the most prominent topic during the conference was the implications of overshoot for global ambition to cut carbon emissions and the viability of the 1.5C limit.
Opening the conference, IIASA director general Prof Hans Joachim Schellnhuber shared his personal view that “1.5C is dead, 2C is in agony and 3C is looming”.
In a pre-recorded keynote speech, Ralph Regenvanu, Vanuatu’s minister for climate change, called for a rejection of the “normalisation of overshoot” and argued that “we must treat 1.5C as the absolute limit that it is” and avoid backsliding. He added:
“Minimising peak warming must be our lodestar, because every tenth of a degree matters.”
Prof Skea opened his keynote with some theology:
“I’m going to start with the prayer of St Augustine as he struggled with his youthful longings: ‘Lord grant me chastity and continence, but not yet.’ And it does seem that this is the way that the world as a whole is thinking about 1.5C: ‘Lord, limit warming to 1.5C above pre-industrial levels, but not yet.’”
Referencing the “lodestar” mentioned by Regenvanu, Skea warned that it is light years away and, “unless we act with a sense of urgency, [1.5C is] likely to remain just as remote”.
Speaking to Carbon Brief on the sidelines of the conference, Skea added:
“We are almost certain to exceed 1.5C and the viability of 1.5C is now much more referring to the long-term potential to limit it through overshoot.”
Schleussner told Carbon Brief that the framing of 1.5C in the conference is “one that further solidifies 1.5C as the long-term limit and, therefore, provides a backstop against the idea of reducing or backsliding on targets”.
If warming is going to surpass 1.5C, the next question is when temperatures are going to be brought back down again, Schleussner added, noting that there has been no “direct” guidance on this from climate policy:
“The [Paris Agreement’s] obligation to “pursue efforts” [to limit global temperature rise by 1.5C] points to doing it as fast as possible. Scientifically, we can determine what this means – and that would be this century. But there’s no clear language that gives you a specific date. It needs to be a period of overshoot – that is clear – and it should be as short as possible.”
In a parallel session on the “highest possible mitigation ambition under overshoot”, Prof Joeri Rogelj, professor of climate science and policy at Imperial College London, outlined how the recent ruling from the International Court of Justice (ICJ) provides guidance to countries on the level of ambition in their climate pledges under the Paris Agreement, known as “nationally determined contributions” (NDCs). He explained:
“[The ruling] highlights that the level of NDC ambition is not purely discretionary to a state and that every state must do its utmost to ensure its NDC reflects the highest possible ambition to meet the Paris Agreement long-term temperature goal.”
Rogelj presented some research – due to be published in the journal Environmental Research Letters – on translating the ICJ’s guidance “into a framework that can help us to assess whether an NDC indeed is following a standard of conduct that can represent the highest level of ambition”. He showed some initial results on how the first two rounds of NDCs measure up against three “pillars” covering domestic, international and implementation considerations.
In the same session, Prof Oliver Geden, senior fellow and head of the climate policy and politics research cluster at the German Institute for International and Security Affairs and vice-chair of IPCC Working Group III, warned that the concept of returning temperatures back down to 1.5C after an overshoot is “not a political project yet”.
He explained that there is “no shared understanding that, actually, the world is aiming for net-negative”, where emissions cuts and CDR together mean that more carbon is being taken out of the atmosphere than is being added. This is necessary to achieve a decline in global temperatures after surpassing 1.5C.
This lack of understanding includes developed countries, which “you would probably expect to be the frontrunners”, Geden said, noting that Denmark is the “only developed country that has a quantified net-negative target” of emission reductions of 110% in 2050, compared to 1990 levels. (Finland also has a net-negative target, while Germany announced its intention to set one last year. In addition, a few small global-south countries, such as Panama, Suriname and Bhutan, have already achieved net-negative.)
Geden pondered whether developed countries are a “little bit wary to commit to going to net-negative territory because they fear that once they say -110%, some countries will immediately demand -130% or -150%” to pay back a larger carbon debt.
Carbon removal
To achieve a decline in global temperatures after an initial breach of 1.5C would require the world to reach net-negative emissions overall.
There is a wide range of potential techniques for removing CO2 from the atmosphere, such as afforestation, direct air capture and bioenergy with carbon capture and storage (BECCS). Captured carbon must be locked away indefinitely in order to be effective at reducing global temperatures.
However, despite its importance in achieving net-negative emissions, there are “huge knowledge gaps around overshoot and carbon dioxide removal”, Prof Skea told Carbon Brief. He continued:
“As it’s very clear from the themes of this conference, we don’t altogether understand how the Earth would react in taking carbon dioxide out of the atmosphere. We don’t understand the nature of the irreversibilities. And we don’t understand the effectiveness of CDR techniques, which might themselves be influenced by the level of global warming, plus all the equity and sustainability issues surrounding using CDR techniques.”
Skea notes that the seventh assessment cycle of the IPCC, which is just getting underway, will “start to fill these knowledge gaps without prejudging what the appropriate policy response should be”.
Prof Nebojsa Nakicenovic, an IIASA distinguished emeritus research scholar, told Carbon Brief that his “major concern” was whether there would be an “asymmetry” in how the climate would respond to large-scale carbon removal, compared to its response to carbon emissions.
In other words, he explained, would global temperatures respond to carbon removal “on the way down” in the same way they did “on the way up” to the world’s carbon emissions.
Nakicenovic noted that overshoot requires a change in focus to approaching the 1.5C limit “from above, rather than below”.
Schleussner made a similar point to Carbon Brief:
“We may fail to pursue [1.5C] from below, but it doesn’t relieve us from the obligation to then pursue it from above. I think that’s also a key message and a very strong overarching message that’s going to come out from the conference that we see…that pursuing an overshoot and then decline trajectory is both an obligation, but it also is well rooted in science.”
Reporting back to the plenary from one of the parallel sessions on CDR, Dr Matthew Gidden, deputy director of the Joint Global Change Research Institute at the Pacific Northwest National Laboratory, also noted another element of changing focus:
“When we’re talking about overshoot, we have become used to, in many cases, talking about what a net-zero world looks like. And that’s not a world of overshoot. That’s a world of not returning from a peak. And so communicating instead about a net-negative world is something that we could likely be shifting to in terms of how we’re communicating our science and the impacts that are coming out of it.”
On the need for both CDR and emissions cuts, Gidden noted that the discussions in his session emphasised that “CDR should not be at the cost of mitigation ambition”. But, he added, there is still the question of how “we talk about emission reductions needed today, but also likely dependence on CDR in the future”.
In a different parallel session, Prof Geden also made a similar point, noting that “we have to shift CDR from being seen as a barrier to ambition to an enabler of even higher ambition, but not doing that by betting on ever more CDR”.
Among the research presented in the parallel sessions on CDR was a recent study by Dr Jay Fuhrman from the JGCRI on the regional differences in capacity to deploy large-scale carbon removal. Ruben Prütz, from the Potsdam Institute for Climate Impact Research, presented on the risks to biodiversity from large-scale land-based CDR, which – in some cases – could have a larger impact than warming itself.
In another talk, the University of Oxford’s Dr Rupert Stuart-Smith explored how individual countries are “depending very heavily on [carbon] removals to meet their climate targets”. Stuart-Smith was a co-author on an “initial commentary” on the legal limits of CDR, published in 2023. This has been followed up with a “much more detailed legal analysis”, which should be published “very soon”, he added.
Impacts of overshoot
Since the Paris Agreement and the call for the IPCC to produce a special report on 1.5C, research into the impacts of warming at the aspirational target has become commonplace.
Similarly, there is an abundance of research into the potential impacts at other thresholds, such as 2C, 3C and beyond.
However, there is comparatively little research into how impacts are affected by overshoot.
The conference included talks on some published research into overshoot, such as the chances of irreversible glacier loss and lasting impacts to water resources. There were also talks on work that is yet to be formally published, such as the risks of triggering interacting tipping points under overshoot.
Speaking in a morning plenary, Prof Debra Roberts, a coordinating lead author on the IPCC’s forthcoming special report on climate change and cities and a former co-chair of Working Group II, highlighted the need to consider the implications of different durations and peak temperatures of overshoot.
For example, she explained, it is “important to know” whether the impacts of “overshoot for 10 years at 0.2C above 1.5C are the same as 20 years at 0.1C of overshoot”.
Discussions during the conference noted that the answer may be different depending on the type of impact. For heat extremes, the peak temperature may be the key factor, while the length of overshoot will be more relevant for cumulative impacts that build up over time, such as sea level rise.
Similarly, if warming is brought back down to 1.5C after overshoot, what happens next is also significant – whether global temperature is stabilised or net-negative emissions continue and warming declines further. Prof Schleussner told Carbon Brief:
“For example, with coastal adaptation to sea level rise, the question of how fast and how far we bring temperatures back down again will be decisive in terms of the long-term outlook. Knowing that if you stabilise that around 1.5C, we might commit two metres of sea level rise, right? So, the question of how far we can and want to go back down again is decisive for a long-term perspective.”
One of the eight themes of the conference centred specifically on the reversibility or irreversibility of climate impacts.
In his opening speech, Vanuatu’s Ralph Regenvanu warned that “overshooting 1.5C isn’t a temporary mistake, it is a catalyst for inescapable, irreversible harm”. He continued:
“No level of finance can pull back the sea in our lifetimes or our children’s. There is no rewind button on a melted glacier. There is no time machine for an extinct species. Once we cross these tipping points, no amount of later ‘cooling’ can restore our sacred reefs, it cannot regrow the ice that already vanished and it cannot bring back the species or the cultures erased by the rising tides.”
As an example of a “deeply, deeply irreversible” impact, Dr Samuel Lüthi, a postdoctoral research fellow in the Institute of Social and Preventive Medicine at the University of Bern, presented on how overshoot could affect heat-related mortality.
Using mortality data from 850 locations across the world, Lüthi showed how projections under a pathway where warming overshoots 1.5C by 0.1-0.3C, before returning to 1.5C by 2100 has 15% more heat-related deaths in the 21st century than a pathway with less than 0.1C of overshoot.
His findings also suggested that “10 years of 1.6C is very similar [in terms of impacts] to five years of 1.7C”.
Extreme heat also featured in a talk by Dr Yi-Ling Hwong, a research scholar at IIASA, on the implications of using solar geoengineering to reduce peak temperatures during overshoot.
She showed that a world where a return to 1.5C had been achieved through geoengineering would see different impacts from a world where 1.5C was reached through cutting emissions. For example, in her modelling study, while geoengineering restores rainfall levels for some regions in the global north, significant drying “is observed in many regions in the global south”.
Similarly, a world geoengineered to 1.5C would see extreme nighttime heat in some tropical regions that is more severe than in a 2C world with no geoengineering, Hwong added.
In short, she said, “this implies the risk of creating winners and losers” under solar geoengineering and “raises concerns about equity and accountability that need to be considered”.
After describing how overshoot features in the outlines of the forthcoming AR7 reports in his opening speech, Prof Skea told Carbon Brief that he expects a “surge of papers” on overshoot in time to be included.
But it was important to emphasise that a “lot of the science that people have been carrying out is relevant within or without an overshoot”, he added:
“At points in the future, we are not going to know whether we’re in an overshoot world or just a high-emissions world, for example. So a lot of the climate research that’s been done is relevant regardless of overshoot. But overshoot is a new kind of dimension because of this issue of focus on 1.5C and concerns about its viability.”
Adaptation
The implications of overshoot temperature pathways for efforts to prepare cities, countries and citizens for the impacts of climate change remains an under-researched field.
Speaking in a plenary, Prof Kristie Ebi – a professor at the University of Washington’s Center for Health and the Global Environment – described research into adaptation and overshoot as “nascent”. However, she stressed that preparing society for the impacts associated with overshoot pathways was as important as bringing down emissions.
She told Carbon Brief that there were “all kinds of questions” about how to approach “effective” adaptation under an overshoot pathway, explaining:
“At the moment, adaptation is primarily assuming a continual increase in global mean surface temperature. If there is going to be a peak – and, of course, we don’t know what that peak is – then how do you start planning? Do you change your planning? There are places, for instance when thinking about hard infrastructure, [where overshoot] may result in a change in your plan.”
IIASA’s Schleussner told Carbon Brief that the scientific community was only just “beginning to appreciate” the need to understand and “quantify” the implications of different overshoot pathways on adaptation.
In a parallel session, Dr Elisabeth Gilmore, associate professor in environmental engineering and public policy at Carleton University in Canada, made the case for overshoot modelling pathways to take greater account of political considerations.
“Not just, but especially, in situations of overshoot, we need to start thinking about this as much as a physical process as a socio-political process…If we don’t do this, we are really missing out on some key uncertainties.”
Current scenarios used in climate research – including the Shared Socioeconomic Pathways and Representative Concentration Pathways – are “a bit quiet” when it comes to thinking about governance, institutions and peace and conflict, Gilmore said. She added:
“Political institutions, legitimacy and social cohesion continue to shift over time and this is really going to shape how much we can mitigate, how much we adapt and especially how we would recover when adding in the dimension of overshoot.”
Gilmore argued that, from a social perspective, adaptation needs are greatest “before the peak” of temperature rise – because this is when society can build the resilience to “get to the other side”. She said:
“Orthodoxy in adaptation [research] that you always want to plan for the worst [in the context of adaptation, peak temperature rise]… But we don’t really know what this peak is going to be – and we know that the politics and the social systems are much more messy.”
Dr Marta Mastropietro, a researcher at Politecnico di Milano in Italy, presented the preliminary results of a study that used emulators – simple climate models – to explore how human development might be impacted under low, medium and high overshoot pathways.
Mastropietro noted how, under all overshoot scenarios studied, both the drop to the human development index (HDI) – an index which incorporates health, knowledge and standard of living – and uncertainty increases as the peak temperature increases.
However, she said “the most important takeaway” from the preliminary results was around society’s constrained ability to recover from damage.
“This percentage of damages that are absorbed is always less than 50%. So, even in the most optimistic scenarios of overshoot, we will not be able to reabsorb these damages, not even half of them. And this is considering a damage function which does not consider irreversible impacts like sea level rise.”
Meanwhile, Dr Inês Gomes Marques from the University of Lisboa in Portugal, shared the results of an as-yet-unpublished study investigating whether the Lisbon metropolitan area holds enough public spaces to offer heatwave relief to the population under overshoot scenarios. The 1,900 “climate refugia” counted by researchers included schools, museums and churches.
Marques noted that most of the population were found to be within one kilometre of a “climate refugia” – but noted that “nuances” would need to be added to the analysis, including a function which considers the limited mobility of older citizens.
She explained that the researchers were aiming to “establish a framework” for this type of analysis that would be relevant to both the science community and municipalities tasked with adaptation. She added:
“The main point is that we need to think about this now, because we will face some big problems if we don’t”.
Legal implications and loss and damage
Significant attention was given throughout the conference to the legal considerations of the breach of – and impetus to return to – the Paris Agreement’s 1.5C warming limit.
This included discussions about how the international legal frameworks should be updated for an “overshoot” world where countries would need to pursue “net-negative” strategies to bring temperatures down to 1.5C.
There were also discussions around governance of geoengineering technologies and the fairness and justice considerations that arise from the real-world impacts of breached targets.
The conference was being held just months after the ICJ’s advisory decision that limiting temperature increase to 1.5C should be considered countries’ “primary temperature goal”.
IIASA’s Shleussner told Carbon Brief that the decision provided “clarity” that countries had a “clear obligation to bring warming back to 1.5C”. He added:
“We may fail to pursue it from below, but it doesn’t relieve us from the obligation to then pursue it from above.”
Prof Lavanya Rajamani, professor of international environmental law at the University of Oxford, insisted that “1.5C was very much alive and well in the legal world”, but noted there were “very significant limits” to what could be achieved through the UN Framework Convention for Climate Change (UNFCCC) – the global treaty for coordinating the response to climate change – both today and in the future.
Summarising discussions around how countries can be pushed to deliver the “highest possible ambition” in future climate plans submitted to the UN, Rajamani urged delegates to be “tempered in [its] expectations of what we’re going to get from the international regime”. She added:
“Changing the narratives and practices at the national level are far more likely to filter up to the international level than trying to do it from a top-down perspective.”
In a parallel session, Prof Christina Voigt, a professor of international law at the University of Oslo, pointed out that overshoot would require countries to aspire beyond “net-zero emissions” as “the end climate goal” in national plans.
Stabilising emissions at “net-zero” by mid-century would result in warming above 1.5C, she explained, whereas “net-negative” emissions are required to deliver overshoot pathways that return temperatures to below the Paris Agreement’s aspirational limit. She continued:
“We will need frontrunners. Leaders, states, regions would need to start considering negative-emission benchmarks in their climate policies and laws from around mid-century. There will be an expectation that developed country parties take the lead and explore this ‘negativity territory’.”
Voigt added that it was “critical” that nations at the UNFCCC create a “shared understanding” that 1.5C remains the “core target” for nations to aim for, even after it has been exceeded. One possible place for such discussions could be at the 2028 global stocktake, she noted.
She said there would need to be more regulation to scale up CDR in a way that addresses “environmental and social challenges” and an effort to “recalibrate policies and measures” – including around carbon markets – to deliver net-negative outcomes.
In a presentation exploring governance of solar radiation management (SRM), Ewan White, a DPhil student in environmental law at the University of Oxford, said the ICJ’s recent advisory opinion could be interpreted to be “both for and against” solar geoengineering.
Countries tasked with drawing up global rules around SRM in an overshoot world would need to take a “holistic approach to environmental law”, White said. In his view, this should take into account international legal obligations beyond the Paris Agreement and consider issues of intergenerational equity, biodiversity protection and nations’ duty to cooperate.
Dr Shonali Pachauri, research group leader at IIASA, provided an overview of the equity and justice implications that might arise in an overshoot world.
First, she said that delays to emissions reductions today are “shifting the burden” to future generations and “others within this generation” – increasing the need for “corrective justice” and potential loss-and-damage payments.
Second, she said that adaptation efforts would need to increase – which, in turn, would “threaten mitigation ambition” given “constrained decision-making”.
Finally, she pointed to resource consumption issues that might arise in a world of overshoot:
“The different technologies that one might use for CDR often depend on the use of land, water, other materials – and this, of course, then means competing with many other uses [of resources].”
A separate stream focused on loss and damage. Session chair Dr Sindra Sharma, international policy lead at the Pacific Islands Climate Action Network, noted that the concept of loss and damage was “fundamentally transformed” by overshoot – adding there were “deep issues of justice and equity”.
However, Sharma said that the literature on loss and damage “has not yet deeply engaged with the specific concept of overshoot” despite it being “an important, interconnected issue”.
Sessions on loss and damage explored the existence of “hard social limits” under future overshoot scenarios, insurance and the need to bring more factors into assessments of habitability, including biophysical and social-economic constraints.
Communication challenges and next steps
At the conference, scientists and legal experts collaborated on a series of statements that summarised discussions at the conference – one for each research theme and an overarching umbrella statement.
IIASA’s Schleussner told Carbon Brief that the statements represented a “key outcome of the conference” that could provide a “framework” to guide future research.
Nevertheless, he noted that statements are a “work in progress” and set to be “further refined” following feedback from experts not able to attend the conference.
At the time of going to press, the overarching conference statement read as follows:
“Global warming above 1.5C will increase irreversible and unacceptable losses and damages to people, societies and the environment.
“It is imperative to minimise both the maximum warming and duration of overshoot above 1.5C to reduce additional risks of human rights violations and causing irreversible social, ecological and Earth system changes including transgressing tipping points.
“This is required by international law and possible by removing CO2 from the atmosphere and further reducing remaining greenhouse emissions.”
Conference organisers also pointed delegates to an open call for research on “pathways and consequences of overshoot” in the journal Environmental Research Letters. The special issue will be guest edited by a number of scientists who played a key role in the conference.
Meanwhile, communications experts at the conference discussed the challenges inherent in conveying overshoot science to non-experts, noting potential confusion around the word “overshoot” and the difficulties in explaining that the 1.5C limit, while breached, was still a goal.
Holly Simpkin, communications manager at the Potsdam Institute for Climate Impact Research, urged caution when communicating overshoot science to the general public:
“I don’t know whether ‘overshoot’ is an effective communication framing. It is an important scientific question, but when it comes to near-term action and the requirements that an ambitious overshoot pathway would ask of us, emissions are what are in our control.
“We could spend 10 more years defining this and, actually, it’s quite complex…I think it’s better to be honest about that and to try to be more simple in that frame of communication, knowing that this community is doing a wealth of work that provides a technical basis for those discussions.”
The post Overshoot: Exploring the implications of meeting 1.5C climate goal ‘from above’ appeared first on Carbon Brief.
Overshoot: Exploring the implications of meeting 1.5C climate goal ‘from above’
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