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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

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.

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.

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).

Global mean temperature anomaly and uncertainty (in degrees C)
Global average surface temperatures for each year, relative pre-industrial, with their respective uncertainties (width of the curves) from the Berkeley Earth surface temperature record. Note that warming is shown here relative to the temperature to the 1850-1900 period. Figure from Berkeley Earth.

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.

Land and ocean temperatures 1850-2023
Land and ocean temperature rise since the pre-industrial 1850-1900 period. Figure from Berkeley Earth.

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.

Global warming by month
Monthly global surface temperatures for each year since 1850, with anomalies shown relative to the pre-industrial 1850-1900 period. Figure from Berkeley Earth.

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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.

Global Warming 1850 to 2023
Annual global surface temperatures since 1850, with anomalies shown relative to the pre-industrial 1850-1900 period for each dataset. Figure from Berkeley Earth.

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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.

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).

Monthly global ocean heat content, 1950-2023
Monthly global ocean heat content (in zettajoules – billion trillion joules, or 10^21 joules) for the 0-2,000 metres for version 3 and version 4 of the IAP dataset. Figure from Cheng et al. (2024).

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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.

Surface temperature anomalies for 2023
Surface temperature anomalies for 2023 from Berkeley Earth. Note that Berkeley uses a 1951-80 baseline to calculate anomalies.

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.

Annual average temperature rankings in 2023
Regions of the world among the five warmest (reds) of five coolest (blues) on record for average annual temperatures in 2023. Figure from Berkeley Earth.

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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.

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.

Factors contributing to global temperature change over the last 10 years
Illustration of contributing factors driving global surface temperatures over the past decade. Figure from Berkeley Earth.

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.

Historical Nino 3.4 sea surface temperature anomalies relative to the ocean average, for 1982-2023.
Niño3.4 sea surface temperature anomalies relative to the ocean average, for 1982-2023. Deviations below 0.5C and above 0.5C are generally used to determine La Niña and El Niño conditions, respectively. Figure from International Research Institute (IRI) at Columbia University.

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.

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.

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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.

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.

Comparing CMIP6 models and observations for 2023
2023 temperatures for both TCR-screened CMIP6 models and observations compared to pre-industrial. Models use the SSP2-4.5 scenario after 2015. Chart by Carbon Brief.

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.

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.

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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.

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.

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.

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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.

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.

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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.

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.)

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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.

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.

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.

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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.

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.

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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.

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.

Expected exceedance years of 1.5C and 2C given a continuation of the long-term warming trend.
Expected exceedance years of 1.5C and 2C given a continuation of the long-term warming trend. Note that exceedance is defined as the long-term average temperature, rather than any individual year. Figure from Berkeley Earth.

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DeBriefed 12 December: EU under ‘pressure’; ‘Unusual warmth’ explained; Rise of climate boardgames

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Welcome to Carbon Brief’s DeBriefed.
An essential guide to the week’s key developments relating to climate change.

This week

EU sets 2040 goal

CUT CRUNCHED: The EU agreed on a legally binding target to reduce greenhouse gas emissions by 90% from 1990 levels by 2040, reported the EU Observer. The publication said that this agreement is “weaker” than the European Commission’s original proposal as it allows for up to five percentage points of a country’s cuts to be achieved by the use of foreign carbon credits. Even in its weakened form, the goal is “more ambitious than most other major economies’ pledges”, according to Reuters.

PETROL CAR U-TURN: Commission president Ursula von der Leyen has agreed to “roll back an imminent ban on the sale of new internal combustion-engined cars and vans after late-night negotiations with the leader of the conservative European People’s Party,” reported Euractiv. Car makers will be able to continue selling models with internal combustion engines as long as they reduce emissions on average by 90% by 2035, down from a previously mandated 100% cut. Bloomberg reported that the EU is “weighing a five-year reprieve” to “allow an extension of the use of the combustion engine until 2040 in plug-in hybrids and electric vehicles that include a fuel-powered range extender”.

CORPORATE PRESSURE: Reuters reported that EU countries and the European parliament struck a deal to “cut corporate sustainability laws, after months of pressure from companies and governments”. It noted that the changes exempt businesses with fewer than 1,000 employees from reporting their environmental and social impact under the corporate sustainability reporting directive. The Guardian wrote that the commission is also considering a rollback of environment rules that could see datacentres, artificial intelligence (AI) gigafactories and affordable housing become exempt from mandatory environmental impact assessments.

Around the world

  • EXXON BACKPEDALS: The Financial Times reported on ExxonMobil’s plans to “slash low-carbon spending by a third”, amounting to a reduction of $10bn over the next 5 years.
  • VERY HOT: 2025 is “virtually certain” to be the second or third-hottest year on record, according to data from the EU’s Copernicus Climate Change Service, covered by the Guardian. It reported that global temperatures from January-November were, on average, 1.48C hotter than preindustrial levels.
  • WEBSITE WIPE: Grist reported that the US Environmental Protection Agency has erased references to the human causes of climate change from its website, focusing instead on “natural processes”, such as variations in the Earth’s orbit. On BlueSky, Carbon Brief contributing editor Dr Zack Labe described the removal as “absolutely awful”.
  • UN REPORT: The latest global environment outlook, a largest-of-its-kind UN environment report, “calls for a new approach to jointly tackle the most pressing environmental issues including climate change and biodiversity loss”, according to the Associated Press. However, report co-chair Sir Robert Watson told BBC News that a “small number of countries…hijacked the process”, diluting its potential impact.

$80bn

The amount that Chinese firms have committed to clean technology investments overseas in the past year, according to Reuters.


Latest climate research

  • Increases in heavy rainfall and flooding driven by fossil-fuelled climate change worsened recent floods in Asia | World Weather Attribution
  • Human-caused climate change played a “substantial role” in driving wildfires and subsequent smoke concentrations in the western US between 1992-2020 | Proceedings of the National Academy of Sciences
  • Thousands of land vertebrate species over the coming decades will face extreme heat and “unsuitable habitats” throughout “most, or even all” of their current ranges | Global Change Biology

(For more, see Carbon Brief’s in-depth daily summaries of the top climate news stories on Monday, Tuesday, Wednesday, Thursday and Friday.)

Captured

A bar chart showing the five factors that account for most of Earth's 'unusual warmth'.

The years 2023 and 2024 were the warmest on record – and 2025 looks set to join them in the top three. The causes of this apparent acceleration in global warming have been subject to a lot of attention in both the media and the scientific community. The charts above, drawn from a new Carbon Brief analysis, show how the natural weather phenomenon El Niño, sulphur dioxide (SO2) emissions from shipping, Chinese SO2, an eruption from the Hunga Tonga-Hunga Ha’apai volcano and solar cycle changes account for most of the “unusual warmth” of recent years. Dark blue bars represent the contribution of individual factors and their uncertainties (hatched areas), the light blue bar shows the combined effects and combination of uncertainties and the red bar shows the actual warming, compared with expectations.

Spotlight

Climate change boardgames

This week, Carbon Brief reports on the rise of climate boardgames.

Boardgames have always made political arguments. Perhaps the most notorious example is the Landlord’s Game published by US game designer and writer Lizzie Magie in 1906, which was designed to persuade people of the need for a land tax.

This game was later “adapted” by US salesman Charles Darrow into the game Monopoly, which articulates a very different set of values.

In this century, game designers have turned to the challenge of climate change.

Best-selling boardgame franchise Catan has spawned a New Energies edition, where players may choose to “invest in clean energy resources or opt for cheaper fossil fuels, potentially causing disastrous effects for the island”.

But perhaps the most notable recent release is 2024’s Daybreak, which won the prestigious Kennerspiel des Jahre award (the boardgaming world’s equivalent of the Oscars).

Rolling the dice

Designed by gamemakers Matteo Menapace and Matt Leacock, Daybreak sees four players take on the role of global powers: China, the US, Europe and “the majority world”, each with their own strengths and weaknesses.

Through playing cards representing policy decisions and technologies, players attempt to reach “drawdown”, a state where they are collectively producing less CO2 than they are removing from the atmosphere.

“Games are good at modelling systems and the climate crisis is a systemic crisis,” Daybreak co-designer Menapace told Carbon Brief.

In his view, boardgames can be a powerful tool for getting people to think about climate change. He said:

“In a video game, the rules are often hidden or opaque and strictly enforced by the machine’s code. In contrast, a boardgame requires players to collectively learn, understand and constantly negotiate the rules. The players are the ‘game engine’. While videogames tend to operate on a subconscious level through immersion, boardgames maintain a conscious distance between players and the material objects they manipulate.

“Whereas videogames often involve atomised or heavily mediated social interactions, boardgames are inherently social experiences. This suggests that playing boardgames may be more conducive to the exploration of conscious, collective, systemic action in response to the climate crisis.”

Daybreak to Dawn

Menapace added that he is currently developing “Dawn”, a successor to Daybreak, building on lessons he learned from developing the first game, telling Carbon Brief:

“I want the next game to be more accessible, especially for schools. We learned that there’s a lot of interest in using Daybreak in an educational context, but it’s often difficult to bring it to a classroom because it takes quite some time to set up and to learn and to play.

“Something that can be set up quickly and that can be played in half the time, 30 to 45 minutes rather than an hour [to] an hour and a half, is what I’m currently aiming for.”

Dawn might also introduce a new twist that explores whether countries are truly willing to cooperate on solving climate change – and whether “rogue” actors are capable of derailing progress, he continued:

“Daybreak makes this big assumption that the world powers are cooperating, or at least they’re not competing, when it comes to climate action. [And] that there are no other forces that get in the way. So, with Dawn, I’m trying to explore that a bit more.

“Once the core game is working, I’d like to build on top of that some tensions, maybe not perfect cooperation, [with] some rogue players.”

Watch, read, listen

WELL WATCHERS: Mother Jones reported on TikTok creators helping to hold oil companies to account for cleaning up abandoned oil wells in Texas.

RUNNING SHORT: Wired chronicled the failure of carbon removal startup Running Tide, which was backed by Microsoft and other tech giants.

PARIS IS 10: To mark the 10th anniversary of the Paris Agreement, climate scientist Prof Piers Forster explained in Climate Home News “why it worked” and “what it needs to do to survive”.

Coming up

Pick of the jobs

DeBriefed is edited by Daisy Dunne. Please send any tips or feedback to debriefed@carbonbrief.org.

This is an online version of Carbon Brief’s weekly DeBriefed email newsletter. Subscribe for free here.

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‘Cali Fund’ aiming to raise billions for nature receives first donation – of just $1,000

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A major biodiversity fund – which could, in theory, generate billions of dollars annually for conservation – received its first donation of just $1,000 in November.

The Cali Fund was created under the UN Convention on Biological Diversity (CBD) at the COP16 nature negotiations in Cali, Colombia, last year.

On 19 November, nine months after the fund officially launched, UK start-up TierraViva AI put forward the first contribution.

The $1,000 payment is an “ice-breaker”, the company’s chief executive tells Carbon Brief, aimed at encouraging others “who may be hesitating” to pay in.

The fund is designed to be a way for companies that rely on nature’s genetic resources to share some of their earnings with the developing, biodiverse countries where many of the original resources are found.

Companies use genetic data from these materials to develop products, such as vaccines and skin cream.

One expert describes the $1,000 as a good “first step”, but says it is “time for larger actors to step forward”. Another says it “squarely points the finger to the profit-making enterprises that are not contributing”.

The CBD is “pleased” about the first payment, a spokesperson tells Carbon Brief, adding that “many discussions” are ongoing about future donations.

Funding biodiversity action

Companies all around the world use genetic materials from plants, animals, bacteria and fungi often found in biodiversity-rich, global south countries to develop their products.

There are existing rules in place to secure consent and ensure compensation if companies or researchers travel to a country to physically gather these materials.

Today, however, much of this information is available in online databases – with few rules in place around access. This genetic data is known as digital sequence information (DSI).

The Cali Fund is part of an effort to close this loophole.

The COP16 agreement on the creation of the fund outlined that large companies in several sectors, including pharmaceutical, cosmetic, biotechnology, agribusiness and technology, “should” contribute a cut of the money they earn from the use of these materials. (See: Carbon Brief’s infographic on DSI.)

The money is intended to fund biodiversity action, with 50% of resources going to Indigenous peoples and local communities who protect vast swathes of the world’s nature and biodiversity.

These contributions, however, are voluntary.

The fund officially launched at the resumed COP16 negotiations in Rome in February 2025, where a spokesperson for the CBD said that first contributions could be announced in spring.

However, Carbon Brief reported in August that the fund was still empty.

On 19 November, the first contribution was announced during the COP30 UN climate summit. At $1,000, the amount was significantly lower than the potential millions that larger companies could pay in. 

A UK government press release described it as a “major milestone” that will “pav[e] the way for others to do the same and mobilise private sector finance for nature at scale”.

The contribution page on the Cali Fund website, which shows the first payment of $1,000.
The contribution page on the Cali Fund website, which shows the first payment of $1,000. Source: Multi-Partner Trust Fund Office.

The payment was an “expression of our commitment to the objectives of the Cali Fund”, TierraViva AI chief executive Dr Paul Oldham wrote in a letter to the executive secretary of the CBD, Astrid Schomaker.

The $1,000 is an “initial contribution”, Oldham said, and the company plans to give more “as our business grows”. Based in the UK with a team of programmers in Nairobi, TierraViva AI was set up in 2023 and uses AI to support conservation.

An anthropologist who worked on Indigenous peoples’ rights in the Amazon, Oldham’s research helped inform the list of sectors most likely to “directly or indirectly benefit from the use of DSI”, including “generative biology” and AI companies.

Oldham noted in a speech at the sidelines of COP30 that although the company’s earnings are not large enough to meet the contribution thresholds set out in the Cali Fund agreement, its contribution showed that companies “of any size” can pay in.

Mary Creagh CBE MP (account name @MaryCreagh_) says in a tweet: "Delighted to announce the first private sector contribution to the Cali fund by UK company Tierra Viva Al. The fund will mobilise private sector finance for nature. At least half will go to indigenous peoples and local communities." A photo is attached to the tweet, showing two men and one woman smiling at the camera.

He tells Carbon Brief that while “some” companies “are not serious about contributing and are seeking to delay” paying into the fund, others have different concerns, including the “need for a level playing field” and positive incentives to contribute:

“This will be hard-earned company money, so it’s reasonable enough to imagine that one of the first questions companies will want an answer to is: ‘well, what is this actually going to be spent on?’ And: ‘what is the benefit of this to us’, which is likely to vary by sector.

“In my view, the best way forward would be for companies that can to make contributions. That would give everybody, including governments, confidence that there might be constructive ways to address difficult topics.” 

Future contributions

A spokesperson for the CBD tells Carbon Brief:

“We are pleased that the Cali Fund is not only ‘open for business’, but that this first contribution also demonstrates it is fully operational. We thank and congratulate TierraViva AI for being the first company to step up.”

“Many discussions” are ongoing around future donations to the fund, the spokesperson says, and the CBD is “hopeful that further announcements can be made soon”, ahead of the next UN biodiversity summit, COP17, in October 2026.

Asked whether the CBD was expecting more contributions at this stage, the spokesperson says the fund was set up in “very short order” and that the first payment shows that companies are “able to contribute”.

US biotechnology company Ginkgo Bioworks was the first to pledge to contribute to the fund earlier this year, but has so far not put forward any money. The company did not respond to Carbon Brief’s request for comment.

Carbon Brief reported earlier this year that at least two companies were contacted by a UK department with opportunities to be involved in the Cali Fund before its launch in February, but no company took up on the offer.

Launch of the Cali Fund at the resumed COP16 negotiations in Rome, Italy on 25 February 2025.
Launch of the Cali Fund at the resumed COP16 negotiations in Rome, Italy on 25 February 2025. Credit: IISD/ENB | Mike Muzurakis.

The first contribution coming from a “startup that has just begun operations squarely points the finger to the profit-making enterprises that are not contributing”, Dr Siva Thambisetty, associate professor of law at the London School of Economics, tells Carbon Brief. Thambisetty adds:

“Strident cries of lack of legal certainty, unfairness or stacking obligations [combining responsibilities from different agreements and laws] would be more credible if industry organisations encouraged large firms that use DSI to begin contributing, instead of denying the last 20 years of multilateral [negotiations] that have led to this point.”

Dr June Rubis – Indigenous peoples and local communities (IPLC) lead from Asia on the Cali Fund’s steering committee – welcomes TierraViva AI’s “first step”, but tells Carbon Brief that the “real test lies ahead” and that it is “now time for larger actors to step forward”.

She says the Cali Fund offers “clarity” on how the private sector can directly increase support to UN-backed funds at a time when “states are retreating” from their climate and biodiversity finance obligations:

“It’s not a voluntary offsetting scheme or a…risky or fringe fund; it’s a multilateral mechanism designed to meet the highest fiduciary and equity standards. We invite companies to see this not as philanthropy, but as participation in a globally endorsed system where trust is institutionalised, benefits are traceable and equity is operationalised.

“Contributing to the Cali Fund isn’t just ethical, it’s strategic. [But] It’s about more than funding: it’s about trust, power-sharing and making sure IPLCs are part of the decisions, not just the outcomes.”

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Net-zero scenario is ‘cheapest option’ for UK, says energy system operator

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A scenario that meets the “net-zero by 2050” goal would be the “cheapest” option for the UK, according to modelling by the National Energy System Operator (NESO).

In a new report, the organisation that manages the UK’s energy infrastructure says its “holistic transition” scenario would have the lowest cost over the next 25 years, saving £36bn a year – some 1% of GDP – compared to an alternative scenario that slows climate action.

These savings are from lower fuel costs and reduced climate damages, relative to a scenario where the UK fails to meet its climate goals, known as “falling behind”.

The UK will need to make significant investments to reach net-zero, NESO says, but this would cut fossil-fuel imports, support jobs and boost health, as well as contributing to a safer climate.

Slowing down these efforts would reduce the scale of investments needed, but overall costs would be higher unless the damages from worsening climate change are “ignored”, the report says.

In an illusory world where climate damages do not exist, slowing the UK’s efforts to cut emissions would generate “savings” of £14bn per year on average – some 0.4% of GDP.

NESO says that much of this £14bn could be avoided by reaching net-zero more cheaply and that it includes costs unrelated to climate action, such as a faster rollout of data centres.

Notably, the report appears to include efforts to avoid the widespread misreporting of a previous edition, including in the election manifesto of the hard-right, climate-sceptic Reform UK party.

Overall, NESO warns that, as well as ignoring climate damages, the £14bn figure “does not represent the cost of achieving net-zero” and cannot be compared with comprehensive estimates of this, such as the 0.2% of GDP total from the UK’s Climate Change Committee (CCC).

Net-zero is the ‘cheapest option’

Every year, NESO publishes its “future energy scenarios”, a set of four pathways designed to explore how the nation’s energy system might change over the coming decades.

(Technically the scenarios apply to the island of Great Britain, rather than the whole UK, as Northern Ireland’s electricity system is part of a separate network covering the island of Ireland.)

Published in July, the scenarios test a series of questions, such as what it would mean for the UK to meet its climate goals, whether it is possible to do so while relying heavily on hydrogen and what would happen if the nation was to slow down its efforts to cut emissions.

The scenarios have a broad focus and do not only consider the UK’s climate goals. In addition, they also explore the implications of a rapid growth in electricity demand from data centres, the potential for autonomous driving and many other issues.

With so many questions to explore, the scenarios are not designed to keep costs to a minimum. In fact, NESO does not publish related cost estimates in most years.

This year, however, NESO has published an “economics annex” to the future energy scenarios. It last published a similar exercise in 2020, with the results being widely misreported.

In the new annex, NESO says that the UK currently spends around 10% of GDP on its energy system. This includes investments in new infrastructure and equipment – such as cars, boilers or power plants – as well as fuel, running and maintenance costs.

This figure is expected to decline to around 5% of GDP by 2050 under all four scenarios, NESO says, whether they meet the UK’s net-zero target or not.

For each scenario, the annex adds up the total of all investments and ongoing costs in every year out to 2050. It then adds an estimate of the economic damages from the greenhouse gas emissions that primarily come from burning fossil fuels, using the Treasury’s “green book”.

When all of these costs are taken into account, NESO says that the “cheapest” option is a pathway that meets the UK’s climate goals, including all of the targets on the way to net-zero by 2050.

It says this pathway, known as “holistic transition”, would bring average savings of £36bn per year out to 2050, relative to a pathway where the UK slows its efforts on climate change.

The overall savings, illustrated by the dashed line in the figure below, stem primarily from lower fuel costs (orange bars) and reduced climate damages (white bars).

In-year energy costs of the “holistic transition” pathway relative to “falling behind”
In-year energy costs of the “holistic transition” pathway relative to “falling behind”, £bn in 2025 prices and assuming central estimates for future fossil-fuel prices. Credit: NESO.

Note that the carbon pricing that is already applied to power plants and other heavy industry under the UK’s emissions trading system (ETS) is excluded from running costs in the annex, appearing instead within the wider “carbon costs” category.

This makes the running costs of fossil-fuel energy sources seem cheaper than they really are, when including the ETS price.

Net-zero requires significant investment

While NESO says that its net-zero compliant “holistic transition” pathway is the cheapest option for the UK, it does require significant upfront investments.

The scale of the additional investments needed to stay on track for the UK’s climate goals, beyond a pathway where those targets are not met, is illustrated in the figure below.

This shows that the largest extra investments would need to be made in the power sector, such as by building new windfarms (shown by the dark yellow bars). This is followed by investment needs for homes, such as to install electric heat pumps instead of gas boilers (dark red bars).

These additional investments would amount to around £30bn per year out to 2050, but with a peak of as much as £60bn over the next decade.

These investments would be offset by lower fuel bills, including reduced gas use in homes (pale red) and lower oil use in transport (mid green).

Notably, NESO says it expects EVs to be cheaper to buy than petrol cars from 2027, meaning there are also significant savings in transport capital expenditure (“CapEx”, dark green).

Detailed breakdown of in-year energy costs of the “holistic transition” pathway relative to “falling behind”
Detailed breakdown of in-year energy costs of the “holistic transition” pathway relative to “falling behind”, £bn in 2025 prices and assuming central estimates for future fossil-fuel prices. Credit: NESO.

Again, the biggest savings in “holistic transition” relative to “falling behind” would come from avoided climate damages – described by NESO as “carbon costs”.

Net-zero cuts fossil-fuel imports

In addition to avoided climate damages, NESO says that reaching the UK’s net-zero target would bring wider benefits to the economy, including lower fuel imports.

Specifically, it says that climate efforts would “materially reduce” the UK’s dependency on overseas gas, with imports falling to 78% below current levels by 2050 in “holistic transition”. Under the “falling behind” scenario, imports rise by 35%”, despite higher domestic production.

This finding, shown in the figure below, is the opposite of what has been argued by many of those that oppose the UK’s net-zero target.

Annual gas imports to the UK
Annual gas imports to the UK, billion cubic metres (bcm) 2024-2050, under different NESO scenarios. Credit: NESO.

NESO goes on to argue that the shift to net-zero would have wider economic benefits. These include a shift from buying imported fossil fuels to investing money domestically instead, which “could bring local economic benefits and support future employment”.

The operator says that there is the “potential for more jobs to be created than lost in the transition to net-zero” and that there would be risks to UK trade if it fails to cut emissions, given exports to the EU – the UK’s main trading partner – would be subject to the bloc’s new carbon border tax.

Beyond the economy, NESO points to studies finding that the transition to net-zero would have other benefits, including for human health and the environment.

It does not attempt to quantify these benefits, but points to analysis from the CCC finding that health benefits alone could be worth £2.4-8.2bn per year by 2050.

Investment is higher for net-zero than for ‘not-zero’

It is clear from the NESO annex that its net-zero compliant “holistic transition” pathway would entail significantly more upfront investment than if climate action is slowed under “falling behind”.

This idea, in effect, is the launchpad for politicians arguing that the UK should walk away from its climate commitments and stop building new low-carbon infrastructure.

As already noted, the NESO analysis shows that this would increase costs to the UK overall.

Still, NESO’s new report adds that “falling behind” would “save” £14bn a year – relative to meeting the UK’s net-zero target – as long as carbon costs are “ignored”.

Specifically, it says that ignoring carbon costs, “holistic transition” would cost an average of £14bn a year more out to 2050 than “falling behind”, which misses the net-zero target. This is equivalent to 0.4% of the UK’s GDP and is illustrated by the solid pink line in the figure below.

In-year energy costs of the “holistic transition” pathway relative to “falling behind”
In-year energy costs of the “holistic transition” pathway relative to “falling behind”, £bn in 2025 prices and assuming central estimates for future fossil-fuel prices. Credit: NESO.

Some politicians are indeed now willing to ignore the problem of climate change and the damages caused by ongoing greenhouse gas emissions. These politicians may therefore be tempted to argue that the UK could “save” £14bn a year by scrapping net-zero.

However, NESO’s report cautions against this, stating explicitly that the “costs discussed here do not represent the cost of achieving net-zero emissions”. It says:

“Our pathways cannot provide firm conclusions over the relative costs attached to the choices between pathways…We reiterate that the costs discussed here do not represent the cost of achieving net-zero emissions.”

It says that the scenarios have not been designed to minimise costs and that it would be possible to reach net-zero more cheaply, for example by focusing more heavily on EVs and renewables instead of hydrogen and nuclear.

Moreover, it says that some of the difference in costs between “holistic transitions” and “falling behind” is unrelated to climate action. Specifically, it says that electricity demand from data centres is around twice as high in “holistic transitions”, adding some £5bn a year in costs in 2050.

In addition, NESO says that most of the “saving” in “falling behind” would be wiped out if fossil fuel prices are higher than expected – falling from £14bn per year to just £5bn a year – even before considering climate damages and wider benefits, such as for health.

Finally, NESO says that failing to make the transition to net-zero would leave the UK more exposed to fossil-fuel price shocks, such as the global energy crisis that added 1.8% to the nation’s energy costs in 2022. It says a similar shock would only cost 0.3% of GDP in 2050 if the country has reached net-zero – as in “holistic transition” – whereas costs would remain high in “falling behind”.

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