In the early 2000s, a new field of climate-science research emerged that began to explore the human fingerprint on extreme weather, such as floods, heatwaves, droughts and storms.
Known as “extreme event attribution”, the field has gained momentum, not only in the science world, but also in the media and public imagination. These studies have the power to link the seemingly abstract concept of climate change with personal and tangible experiences of the weather.
Scientists have published more than 400 peer-reviewed studies looking at weather extremes around the world, from wildfires in the US and heatwaves in India and Pakistan to typhoons in Asia and record-breaking rainfall in the UK. The result is mounting evidence that human activity is raising the risk of some types of extreme weather, especially those linked to heat.
To track how the evidence on this fast-moving topic is stacking up, Carbon Brief has mapped – to the best of our knowledge – every extreme-weather attribution study published to date.
Carbon Brief’s analysis reveals:
- 71% of the 504 extreme weather events and trends included in the map were found to be made more likely or more severe by human-caused climate change.
- 9% of events or trends were made less likely or less severe by climate change, meaning 80% of all events experienced some human impact. The remaining 20% of events and trends showed no discernible human influence or were inconclusive.
- Of the 152 extreme heat events that have been assessed by scientists, 93% found that climate change made the event or trend more likely or more severe.
- For the 126 rainfall or flooding events studied, 56% found human activity had made the event more likely or more severe. For the 81 drought events studied, it’s 68%.
First published in July 2017, this article is the fifth annual update (see endnote) to incorporate new studies. The aim is that it serves as a tracker for the evolving field of “extreme event attribution”.
Using the map
The map above shows 504 extreme weather events and trends across the globe for which scientists have carried out attribution studies. The different symbols show the type of extreme weather; for example, a heatwave, flood or drought. The colours indicate whether the attribution study found a link to human-caused climate change (red), no link (blue) or was inconclusive (grey).
Use the plus and minus buttons in the top-left corner, or double click anywhere, to zoom in on any part of the world. Click on a symbol to reveal more information, including a quote from the original paper to summarise the findings and a link to the online version.
The filter on the left allows users to select a specific type of weather event to look at or, for example, only those found to be influenced by climate change.
The filter can also be used to highlight extreme events from a particular year. (Note: earlier versions of this map classified events by the year that the study or analysis was published.) To isolate studies that assess the changing trends of weather extremes, click the “trend” box in the filter.
The software used to make the map currently only works with a Web Mercator projection (as used by virtually all major online map providers). It is worth noting that this – like all map projections – offers a somewhat distorted view of the world.
It is important to note that the weather events scientists have studied so far are not randomly chosen. They can be high-profile events, such as Hurricane Harvey, or simply the events that occurred nearest to scientific research centres. (More on this below.)
The map includes three different types of studies. The circles and hexagons on the map indicate papers published in peer-reviewed journals. The different shapes refer to whether the study considers an individual extreme event (circles), such as a wildfire or storm, or whether it analyses longer-term trends in extreme weather (hexagons), such as the change in frequency of flooding or marine heatwaves over time.
The third shape – triangles – indicate rapid attribution studies. These are quickfire assessments of the climate change contribution to extreme weather events, published online shortly after an event concludes. (More on this below.)
Finally, it is worth noting that some of the icon locations are approximate – particularly for studies that cover large regions. For example, global studies can be found grouped together in the middle of the Atlantic Ocean.
Extreme weather types
The events and trends shown on the map are covered by 431 individual scientific papers or rapid studies. Where a single study covers multiple events or locations, these have been separated out into individual entries on the map.
Combining the evidence over the past 20 years, the literature is heavily dominated by studies of extreme heat (30%), rainfall or flooding (25%) and drought (16%). Together, these make up more than two-thirds of all published studies (71%). The full list is available in this Google sheet.
As the chart below shows, the number of extreme events studied has grown substantially over the past 10-15 years. Note that formal studies typically follow a year or so after the event itself as the writing and peer-review process for journal papers can take many months.
The majority of studies included here have been published in the annual “Explaining extreme events” special issues of the Bulletin of the American Meteorological Society (BAMS). Each bumper volume typically contains around 15-30 peer-reviewed studies of events from the previous year. Other studies have been found through the Climate Signals database and online searches through journals. This update includes studies published up to the end of May 2022.
(Note: The map currently only includes studies published in English.)
Specific types of event can be displayed in the chart below by clicking on the category names at the top.
Number of attribution studies by extreme weather event type and year. Note: the total number of events dipped in 2017 because the Bulletin of the American Meteorological Society special report for that year was published in early 2018 rather than late 2017. Chart by Carbon Brief using Highcharts.
Most of the categories of extreme weather are self-explanatory, but “storms” and “oceans” require a bit of explanation.
For ease of presentation, the “storms” category includes both tropical cyclones – such as hurricanes and typhoons – and extratropical storms. The “oceans” category encompasses studies looking at marine heatwaves, storm surges and the strength of El Niño events.
Newer categories include “coral bleaching” and “ecosystem services”, reflecting the ongoing developments in attribution science. For example, a rapid attribution study concluded that climate change had “drastically” increased the likelihood of the conditions leading to bleaching of the Great Barrier Reef in 2016 – by at least 175 times. And a 2022 study found that “extremely early” cherry-tree flowering in Kyoto in March 2021 was made “15 times more likely” by climate change.
For this latest iteration of the map, a new category of “compound” extreme events has also been added. This includes, for example, a 2021 study that found climate change had contributed to the “high likelihood” of combined dry and hot events in recent decades over most of China.
Such studies show that attribution studies are increasingly considering the impacts of extremes, rather than focusing purely on the weather event.
One of the first of these “impact attribution” studies was published in 2016. It estimated that 506 of the 735 fatalities in Paris during the 2003 European heatwave were down to the fact that climate change had made the heat more intense than it would otherwise have been. The same was true for 64 of the 315 fatalities in London, the study said. Health impacts have increasingly become a focus of attribution studies.
Similarly, a 2021 study found that 37% of “warm-season heat-related deaths” across 43 countries between 1991 and 2018 “can be attributed to anthropogenic climate change and that increased mortality is evident on every continent”. Another 2021 study, which the authors unpacked in a Carbon Brief guest post, found that climate change was a “critical driver” of the drought that led to a food crisis in Lesotho in 2007. And a third 2021 study – also the subject of a Carbon Brief guest post – on the rising threat of an “outburst flood” from glacial lakes in the Peruvian Andes found that the retreat of the region’s glaciers was “entirely attributable” to human-caused warming.
This shift towards impacts “is quite significant”, says Prof Peter Stott, who leads the climate monitoring and attribution team at the Met Office Hadley Centre and has been a co-editor of the BAMS reports since they began in 2012. He tells Carbon Brief:
“Impacts are hard to do because you have to establish a significant link between the meteorology and the impact in question. As editors, we’ve been trying to encourage more studies on impacts because it’s the impacts rather than the meteorology per se that tends to motivate these types of study – and if we only have the attribution on the meteorological event then we only have an indirect link to the relevant impact.”
Attribution of climate impacts could even be used in the courts, one 2021 study explained. The authors wrote a Carbon Brief guest post explaining how attribution science can be “translated into legal causality”. They wrote:
“Attribution can bridge the gap identified by judges between a general understanding that human-induced climate change has many negative impacts and providing concrete evidence of the role of climate change at a specific location for a specific extreme event that already has led or will lead to damages.”
Finally, attribution research has also identified the “signal” of human influence in other indicators of climate change, such as increasing average temperature, rising lake temperatures or sea level rise. Recent research has even been able to detect the fingerprint of climate change “from any single day in the observed global record since early 2012, and since 1999 on the basis of a year of data”. These types of studies have not been included in the attribution map as the focus here is on extremes.
Human influence on extreme weather
Of the attribution studies included here, scientists found that human-caused climate change has altered the likelihood or severity of an extreme weather event in 80% of cases studied (71% made more severe or likely and 9% made less so).
In Carbon Brief’s first edition of this analysis in 2017, 68% of events were found to have a human impact (with 63% made more severe or likely and 6% less so).
While these figures are not representative of all extreme weather events – attribution studies have only been conducted on a relatively small number – previous research has taken this broader view. For example, a 2015 study estimated the fraction of all globally occurring heat and heavy rainfall extremes that was attributable to warming. The authors found that around 75% of “moderate daily hot extremes over land” and 18% of “moderate daily precipitation extremes over land” were attributable to the observed temperature increase since pre-industrial times. These fractions are expected to increase with further warming, the authors noted.
There are several ways of carrying out an attribution analysis. (A team of attribution scientists wrote a Carbon Brief guest post in 2021 that unpacks their methods.) One of the most common is to take observations and/or climate model simulations of an extreme event in the current climate and compare them with idealised model runs of that event in a world without human-caused global warming. The difference between the “with” and “without” climate change simulations indicates how the likelihood or severity of that extreme event has changed.
Note that events are classified here as having an human impact if climate change is found to have influenced at least one aspect of that event. For example, a study of the 2011 East Africa drought found that climate change contributed to the failure of the “long rains” in early 2011, but that the lack of “short rains” in late 2010 was down to the climate phenomenon La Niña. This event is, thus, designated as having a human impact.
For the majority of events affected by climate change, the balance has shifted in the same direction. That is, rising temperatures made the event in question more severe or more likely to occur. These events are represented by the red in the chart below. Clicking on the red “slice” reveals that heatwaves account for 40% of such events, rainfall or flooding for 20%, and droughts for 15%. Return to the original chart, and do the same with the other slices to see the proportion of different weather types in each category.
Pie chart showing the proportion of extreme events/studies that were found to have been made more likely/severe by climate change (red segment), less likely/severe (orange), had no link identified (blue) and were inconclusive or lacked sufficient data (grey). Clicking on a segment reveals the makeup of different types of extremes within that category. Chart by Carbon Brief using Highcharts.
In 11% of extreme weather events and trends studied, scientists found no discernible influence from human activity. These are coloured blue in the map and the chart above. For a further 9%, the observational data or modelling techniques used in the study were insufficient to reach a reliable conclusion (shown as grey in the map and pie chart).
In 9% of studied weather events and trends, scientists found climate change had made the event less likely or less severe (pale orange in the chart above).
Unsurprisingly, this category includes blizzards and extreme cold snaps. However, it also features a few studies that suggest climate change has lessened the chances of heavy rainfall, and another that found rising temperatures have made agricultural drought in California less likely.
Drought is complicated (more on this below). Briefly, though, it is worth noting that five other studies looking at different aspects of the California drought over 2011-17 found climate change had played a role. Two found no discernible link (pdf, p7-15), while one was inconclusive (pdf, p3).
Interestingly, a 2020 study analysed the way links between climate change and the California drought were portrayed in US media. It finds that the links were “covered widely in both local and national news”, but notes:
“However, legitimate differences in the methods underpinning the attribution studies performed by different researchers often resulted in a frame of scientific uncertainty or disagreement in the media coverage.”
As the case of California’s drought shows, it is often necessary to dig deeper to understand the full picture. The rest of this article looks at the evidence for the three most-studied types of extreme weather – heatwaves, heavy rain and floods, and droughts – as well as some of the main issues in event attribution, and where the field as a whole is heading.
Heatwaves
The attribution map includes studies of 152 extreme heat events, of which 142 (93%) have been made more likely or more severe because of climate change. No studies have found a heatwave that has been made less severe by climate change, while studies of two events (1%) identified no influence and a further eight (5%) were inconclusive.
In recent years, studies have shown that several heat extremes would have been impossible or virtually impossible without human influence on the climate. These include Siberia’s heatwave of 2020, the Pacific north-west “heat dome” event of 2021 and Europe’s record-breaking summer of 2021.
The studies on extreme heat that did not find a role for climate change were an analysis of the Russian heatwave in 2010 and a rapid attribution study of the all-time high temperatures recorded in Rajasthan, India in May 2016. For the latter, the authors suggested that “the lack of a detectable trend may be due to the masking effect of aerosols on global warming and increased use of irrigation”.
While heatwaves are the most-studied extreme event in attribution literature, they are becoming “less and less interesting for researchers”, notes a Bloomberg article from 2020. Dr Friederike Otto is a senior lecturer at the Grantham Institute for Climate Change and the Environment at Imperial College London and co-leader of World Weather Attribution, a consortium of scientific organisations founded in 2014 to deliver “timely and scientifically reliable information on how extreme weather may be affected by climate change”. She told Bloomberg that the consortium chose not to investigate California’s record-breaking summer 2020 heatwave as “the evidence is so strong already”.
A particularly well-studied region for heatwaves in the literature is Australia, which accounts for 10% of the heat-related events included here. And climate change was found to play a role in all but one of the 15 Australian heat events studied. It is worth noting for that one event, however, that although the study (pdf, p145) was inconclusive for the city of Melbourne in south-east Australia, the authors did detect a human influence on extreme heat up the coast in Adelaide.
This raises a few important points. First, finding that climate change contributed to an event is not the same as saying it “caused” that event. Attribution is about working out if the likelihood or magnitude of a particular event happening now is different from what it would be in a world that was not warming.
A useful analogy – as explained in the first BAMS report in 2012 – is of a baseball player who starts taking steroids. If the player begins hitting 20% more home runs than before, it would not be possible to say for sure whether a particular home run is because of the steroids or the player’s spontaneous skill. But it is possible to say how the steroids have altered the likelihood that the player hits a home run, by comparing their current and historical performances. As the report put it:
“Given that steroids have resulted in a 20% increased chance that any particular swing of the player’s bat results in a home run, you would be able to make an attribution statement that, all other things being equal, steroid use had increased the probability of that particular occurrence by 20%.”
Another important point is that in cases where attribution science finds that climate change is making a given type of extreme weather more likely, it does not necessarily follow that the chance of experiencing that kind of weather gets incrementally higher each year. Natural variability means that there will still be ups and downs in the strength and frequency of extreme events.
Finally, there is usually a level of confidence attached to attribution results. So, while two studies might both find a role for human influence in a given weather event, the signal may be stronger for one than the other. For the purposes of this analysis, the attribution map does not distinguish between high- and low-confidence results, but users can click through to each study for more details.
Heavy rain and flooding
Of the 126 rainfall or flooding events included in the attribution map, 71 (56%) found human activity had made the event more likely or more severe – a far smaller proportion than for heat-related studies. Nineteen studies (15%) found that climate change had made the whole event less likely to occur. Of the remaining heavy rainfall events, studies of 24 (19%) found no evidence of a link to climate change, while 12 (10%) were inconclusive.
That there is a more divided set of results for extreme rainfall than for heatwaves could suggest several things. In some cases, limited data might make it difficult to detect a clear “signal” of climate change above the “noise” of weather considered normal for a particular region. In other cases, an inconclusive result could reflect the fact that rainfall or flooding events are inherently more complex than heatwaves, with many ways for natural variability to play a role. Human factors, such as land use and drainage, also play a part in whether heavy rain leads to flooding.
Take the UK, for example. While one study found climate change had increased the risk of floods in England and Wales in Autumn 2000 by at least 20% (and even up to 90%), another found little influence on summer rainfall in 2012 (pdf, p36).
This raises another important point. When it comes to interpreting the results of event attribution studies, it matters what the question is. For example, a 2013 study asked whether recent wet summers in north-western Europe were a response to retreating Arctic sea ice (pdf, p32). The answer from the study was “no”. But, as a foreword from that year’s BAMs report explains:
“Given the numerous ways climate change could influence precipitation in this region, a ‘no’ result for the role of Arctic sea ice should not be interpreted as an absence of any role at all for climate change.”
This is similar to an argument made by Dr Kevin Trenberth, distinguished senior scientist at the National Center for Atmospheric Research, and colleagues in a Nature Climate Change “perspective” article in 2015.
The paper notes that, in a chaotic weather system, the complex dynamics of the atmosphere mean the size and path of a storm or heavy rainfall event has a large element of chance. This can make it tricky to identify where climate change fits in, potentially underestimating its influence.
Therefore, rather than analysing the weather patterns that bring a storm to an area, the authors argue that scientists should be looking at how the impact of that storm has been boosted by temperature changes – known as “thermodynamic” effects. Higher temperatures mean warmer seas, higher sea levels and more moisture evaporating into the atmosphere. These are changes that scientists can be more confident in, the authors wrote, and so should be the focus for attribution studies – rather than looking at changes to circulation patterns in the atmosphere.
For example, the paper reexamines an earlier study (pdf, p15) that suggested climate change had reduced the chances of the five-day heavy rainfall event that hit north-east Colorado in September 2013. Trenberth and colleagues argue that while climate change might not have made the specific weather system that brought the rain more likely, it will have contributed to the sheer volume of moisture in the atmosphere.
Chart shows the number of studies for each type of extreme event that fall within each category of human influence: More severe/likely (red), less severe/likely (yellow), no influence (blue) and inconclusive (grey). Chart by Carbon Brief using Highcharts.
While attribution studies of heatwaves are generally more straightforward than storms – as they focus on thermodynamic influences – the type of question they are asking is still important. The Russian heatwave in 2010 is a good example of this. One study looking at the severity of the event did not find a role for climate change. Yet another one, which did find an influence, looked at the likelihood of the event.
This apparent contradiction is tackled by a third study that reconciles the other two. It explains that “the same event can be both mostly internally-generated [i.e. by natural variability] in terms of magnitude and mostly externally-driven [i.e. by human-caused climate change] in terms of occurrence probability”.
Otto, who is lead author of the third study, tells Carbon Brief:
“The studies, thus, only appear to be contradictory, but are, in fact, complementary.”
It is also important to stress that the absence of evidence for a link to climate change is not the same as evidence of absence. In other words, it does not necessarily mean there was no human influence, just that a particular analysis did not find one. This is why a single study should never be considered the final word on how climate change influences a given type of extreme weather.
Drought
Of the 81 drought events and trends considered here, climate change was found to have increased the severity or likelihood of 55 (68%). Of the remainder, the likelihood or severity was reduced for one event (1%), while no discernible link with human activity was found for 15 (19%) and 10 (12%) were inconclusive.
Capetonians queue for water at natural springs around the city during the water crisis, January 2018. Credit: tim wege / Alamy Stock Photo
This mixed bag of results reflects the inherent complexity of droughts. And, again, the specific question matters. Conclusions about the role of climate change in a specific drought could depend on whether a study looks at temperature, rainfall or soil moisture, for example.
As the 2015 BAMS report explains:
“Drought continues to be an event type where the results require significant context, and easy answers often remain elusive because of the many meteorological, hydrological, and societal drivers that combine to cause drought.”
(For more on the different ways that droughts can be categorised, see this Carbon Brief guest post from 2018.)
Geographical reach
While much has been achieved in the field of extreme event attribution in a short space of time, scientists are constantly looking for ways to tailor their work to suit the people who might use it.
One major goal since the early days of the field has been to expand extreme event attribution to cover a larger and more diverse geographical area.
Where in the world scientists can carry out attribution studies – and for what kind of events – will always be limited by the quality and availability of observed data and appropriate models. The attribution map highlights, for example, that there are relatively few studies of extreme weather in Africa and South America.
In another example, scientists hoping to analyse Super Typhoon Mangkhut – which hit the Philippines in September 2018 – were unable to in part because of “very poor quality” observed data in publicly available datasets and a lack of models.
At the moment, there is also a heavy leaning towards weather events that are local to the modelling groups, or that have a particular scientific interest. Otto explains:
“For example, scientists often do attribution studies because an event occurs on their doorstep. The UK, California and Boulder [in Colorado] are, therefore, studied much more than other parts of the world, but that does not necessarily make them places particularly impacted by climate change.”
This means that while the studies carried out so far are indicative of the role climate change is playing in extreme weather around the world, they should not be considered representative of all types of extreme weather everywhere, says Otto. She tells Carbon Brief:
“[The studies so far] are part of a picture, but we don’t know what’s on the missing puzzle pieces. And, crucially, we don’t know how many pieces are missing.”
For example, Otto recently penned a Carbon Brief guest post on how the lack of monitoring of heatwaves in Africa means they are a “forgotten impact” of climate change.
Real-time extreme weather attribution
As well as expanding the science to cover different types of weather and more of the world, scientists are getting faster at turning the handle on extreme event attribution studies – sometimes crunching the numbers just days after an event has occurred.
The rapid studies included here are all produced by the World Weather Attribution (WWA) initiative, described earlier, or the UK Met Office.
An example of analysis performed by the latter includes their review of the UK’s weather in 2020, which was published by Carbon Brief. This showed that climate change increased the likelihood of the UK’s warm year by approximately a factor of 50.
While the WWA individual rapid assessments are not individually peer-reviewed, they are conducted using methods that have been through the peer-review process. As the 2014 BAMS report explains:
“Much like other routine analysis, such as an operational seasonal forecast, statements made about heat events using these methods do not necessarily need to go through the peer-reviewed literature to be considered credible.”
By conducting the analysis in the immediate aftermath of a weather event, these rapid studies provide almost-real-time information on the influence of climate change, rather than having to wait many months for a formal study.
(In some cases, these rapid assessments are later published in peer-reviewed journals. In these instances, the formal study is included in the attribution map, rather than the initial analysis. In some cases, this means earlier rapid assessments are removed from the Carbon Brief map in order to add in the relevant peer-reviewed paper once it is published.)
The European Centre for Medium-Range Weather Forecasts (ECMWF) has been working on a pilot “operational attribution service” through the Copernicus Climate Change Service (C3S).
This collaboration between the UK Met Office, German weather service (DWD), Meteo France, Dutch weather service (KNMI) and the University of Oxford will “demonstrate how attribution of extreme weather events can be carried out operationally by national meteorological services”, Prof Stott tells Carbon Brief:
“In this project we are developing and testing the protocols we will need to enable rapid and reliable assessments of the extent to which recent extreme weather events have been made more or less intense or more or less likely by climate change. We started at the beginning of the year and so far we have tested our procedures on an analysis of the 2018 heatwave in Europe.”
The progress to date has “demonstrated the importance of international collaboration for developing new techniques and processes”, says Stott. But “national meteorological services across Europe will continue to have a particular remit to deliver advice on weather and climate in their own countries”, he adds:
“At the Met Office in the UK we are developing our operational attribution capability to help inform the public, policymakers and journalists about the extent to which damaging extreme weather events like the floods in Yorkshire [in 2019] have been affected by climate change.”
An evolving science
As the science of extreme event attribution has matured and become more nuanced, so has the choice of terminology around extreme weather and climate change.
While some attest that all extreme weather must be affected by a world that is warming, this warrants some caution. As the first BAMS report in 2012 noted:
“While it has been argued that in the Anthropocene, all extreme weather or climate events that occur are altered by human influence on climate…this does not mean that climate change can be blamed for every extreme weather or climate event. After all, there has always been extreme weather.”
But while it would be premature to suggest that any single study is the last word, it is clear that – in many cases – the science can do better than that. Similarly, scientific thinking has clearly moved on from the unsatisfactory statement that it is not possible to attribute any individual weather event to climate change. Indeed, as mentioned earlier, there have been some studies that have concluded that an event – or aspect of an event – would have been impossible without climate change.
Ultimately, there are no blanket rules in attribution. Scientists need to examine the circumstances of each individual weather event – or a longer pattern of events for trend studies. It is only by combining evidence from all around the world that they can begin to draw broader conclusions.
Attribution studies, therefore, rely heavily on the quality and availability of observational data and climate model simulations. In a short paper for the journal Weather, Dr Otto says that “the models used for attribution need to be able to reliably estimate the likelihoods of the types of events being attributed”.
As discussed earlier, attribution studies of heatwaves tend to be more straightforward because of their focus on thermodynamic effects, rather than atmospheric circulation. Yet, Otto tells Carbon Brief that recent studies suggest models overestimate the year-to-year variability of heat extremes in some parts of the world, and thus underestimate the trend and the role of climate change.
In a rapid attribution study of the western Europe summer heatwave in 2019, for example, Otto and her colleagues found that, for the month of June, the models “show about 50% smaller trends than observations in this part of Europe and much higher year-to-year variability than the observations”. Similarly, a study of the 2019-20 Australian bushfires noted that “models underestimate the observed trend in heat” and so the “real increase could be much higher”.
These findings emphasise how important it is to analyse models and observations together, Otto says:
“This made me realise just how important attribution is for the scientific community – and everyone using climate science – at bringing observations and models together in a very concrete real-world test case.
Attribution can, therefore, be used to help scientists “identify where the models are doing well and for what they are not in a much more direct way than the classical skill assessment of climate projections does”, adds Otto.
Forecasted attribution
One attempt to move attribution science forward was the very first “advance forecasted” attribution analysis, which quantified the impact of climate change on the size, rainfall, and intensity of Hurricane Florence before it made landfall in North Carolina in September 2018.
The analysis ran two sets of short-term forecasts for the hurricane: one as the climate is today and the other in a simulated world without human-caused climate change. The researchers concluded at the time:
“We find that rainfall will be significantly increased by over 50% in the heaviest precipitating parts of the storm. This increase is substantially larger than expected from thermodynamic considerations alone. We further find that the storm will remain at a high category on the Saffir-Simpson scale for a longer duration and that the storm is approximately 80km in diameter larger at landfall because of the human interference in the climate system.”
The analysis received a mixed reaction. Prof Stott told Carbon Brief that it was “quite a cool idea”, but would be dependent on being able to forecast such events reliably. Dr Kevin Trenberth, distinguished senior scientist at the National Center for Atmospheric Research, described it as “a bit of a disaster”. He told Carbon Brief that the quality of the forecast was questionable for the assessment:
“The forecasts made were not good: the intensity of the forecast storm at landfall was category 4 or 5 as I recall, instead of category 2. And so the statements made were based on quite flawed assumptions: namely, that they had a good forecast.”
A key requirement for a reliable attribution study is for models to accurately replicate the extreme event, Trenberth added, but “obviously one can not assess the goodness of the forecast if one does this in advance”.
The authors subsequently published a paper in Science Advances that “reviews the forecasted attribution with the benefit of hindsight”. The findings show that climate change increased rainfall amounts “associated with the forecasted storm’s core” by around 5%, and contributed to Hurricane Florence being “about 9km larger in mean maximum diameter (or a 1.6% increase in storm area) due to climate change”.
The authors acknowledged that the “quantitative aspects of our forecasted attribution statements fall outside broad confidence intervals of our hindcasted statements and are quite different from the hindcasted best estimates”. In short, the results are quite a way off what they forecasted.
However, the authors also said they have identified what went wrong with their forecasted analysis. Problems with the way their “without climate change” model runs were set up created a larger contrast against their real-world simulations. The results thus suggested that climate change would have a bigger impact than it actually did.
Nonetheless, the study did identify a quantifiable impact of climate change on Hurricane Florence, adding to the evidence from studies by other author groups, the researchers concluded:
“As the climate continues to warm, it is expected that extreme tropical cyclone precipitation events and resulting inland flooding will become yet more frequent.”
In addition, a 2021 study of the record Australian heat event of October 2015 noted the potential of their methods “to provide attribution statements for forecast events within an outlook period”. This will “allow for informed messaging to be available as required when an extreme event occurs, which is of particular use to weather and climate services”, the authors wrote.
On the topic of forecasts, a 2021 study showed how it was possible to use a weather forecast model for attribution. The researchers, who penned a Carbon Brief guest post about their work, tested their methods using the European heatwave of February 2019 – an event their model successfully predicted:
“We find that the direct impact of the extra carbon dioxide (CO2) that humans have pumped into the atmosphere made the event 42% more likely for the British Isles and at least 100% (two times) more likely for France.”
Their work “so far represents just the first few steps towards an operational forecast-based attribution system”, they noted.
Finally, as well as casting forwards, attribution can also look back in time. A 2020 study on the US “Dust Bowl” heat and drought events of the 1930s takes an unconventional approach of looking at how the past event “would behave” with present-day levels of greenhouse gases.
The researchers find that “the return period of a 1-in-100-year heatwave summer (as observed in 1936) would be reduced to about 1-in-40 years” in today’s climate.
Carbon Brief will continue to add new extreme event attribution studies to the map and update the accompanying analysis every year. Please get in touch with any suggestions of attribution studies that could be included.
The post Mapped: How climate change affects extreme weather around the world appeared first on Carbon Brief.
https://www.carbonbrief.org/mapped-how-climate-change-affects-extreme-weather-around-the-world/
Greenhouse Gases
DeBriefed 9 January 2026: US to exit global climate treaty; Venezuelan oil ‘uncertainty’; ‘Hardest truth’ for Africa’s energy transition
Welcome to Carbon Brief’s DeBriefed.
An essential guide to the week’s key developments relating to climate change.
This week
US to pull out from UNFCC, IPCC
CLIMATE RETREAT: The Trump administration announced its intention to withdraw the US from the world’s climate treaty, CNN reported. The move to leave the UN Framework Convention on Climate Change (UNFCCC), in addition to 65 other international organisations, was announced via a White House memorandum that states these bodies “no longer serve American interests”, the outlet added. The New York Times explained that the UNFCCC “counts all of the other nations of the world as members” and described the move as cementing “US isolation from the rest of the world when it comes to fighting climate change”.
MAJOR IMPACT: The Associated Press listed all the organisations that the US is exiting, including other climate-related bodies such as the Intergovernmental Panel on Climate Change (IPCC) and the International Renewable Energy Agency (IRENA). The exit also means the withdrawal of US funding from these bodies, noted the Washington Post. Bloomberg said these climate actions are likely to “significantly limit the global influence of those entities”. Carbon Brief has just published an in-depth Q&A on what Trump’s move means for global climate action.
Oil prices fall after Venezuela operation
UNCERTAIN GLUT: Global oil prices fell slightly this week “after the US operation to seize Venezuelan president Nicolás Maduro created uncertainty over the future of the world’s largest crude reserves”, reported the Financial Times. The South American country produces less than 1% of global oil output, but it holds about 17% of the world’s proven crude reserves, giving it the potential to significantly increase global supply, the publication added.
TRUMP DEMANDS: Meanwhile, Trump said Venezuela “will be turning over” 30-50m barrels of oil to the US, which will be worth around $2.8bn (£2.1bn), reported BBC News. The broadcaster added that Trump claims this oil will be sold at market price and used to “benefit the people of Venezuela and the US”. The announcement “came with few details”, but “marked a significant step up for the US government as it seeks to extend its economic influence in Venezuela and beyond”, said Bloomberg.
Around the world
- MONSOON RAIN: At least 16 people have been killed in flash floods “triggered by torrential rain” in Indonesia, reported the Associated Press.
- BUSHFIRES: Much of Australia is engulfed in an extreme heatwave, said the Guardian. In Victoria, three people are missing amid “out of control” bushfires, reported Reuters.
- TAXING EMISSIONS: The EU’s landmark carbon border levy, known as “CBAM”, came into force on 1 January, despite “fierce opposition” from trading partners and European industry, according to the Financial Times.
- GREEN CONSUMPTION: China’s Ministry of Commerce and eight other government departments released an action plan to accelerate the country’s “green transition of consumption and support high-quality development”, reported Xinhua.
- ACTIVIST ARRESTED: Prominent Indian climate activist Harjeet Singh was arrested following a raid on his home, reported Newslaundry. Federal forces have accused Singh of “misusing foreign funds to influence government policies”, a suggestion that Singh rejected as “baseless, biased and misleading”, said the outlet.
- YOUR FEEDBACK: Please let us know what you thought of Carbon Brief’s coverage last year by completing our annual reader survey. Ten respondents will be chosen at random to receive a CB laptop sticker.
47%
The share of the UK’s electricity supplied by renewables in 2025, more than any other source, according to Carbon Brief analysis.
Latest climate research
- Deforestation due to the mining of “energy transition minerals” is a “major, but overlooked source of emissions in global energy transition” | Nature Climate Change
- Up to three million people living in the Sudd wetland region of South Sudan are currently at risk of being exposed to flooding | Journal of Flood Risk Management
- In China, the emissions intensity of goods purchased online has dropped by one-third since 2000, while the emissions intensity of goods purchased in stores has tripled over that time | One Earth
(For more, see Carbon Brief’s in-depth daily summaries of the top climate news stories on Monday, Tuesday, Wednesday, Thursday and Friday.)
Captured
The US, which has announced plans to withdraw from the UNFCCC, is more responsible for climate change than any other country or group in history, according to Carbon Brief analysis. The chart above shows the cumulative historical emissions of countries since the advent of the industrial era in 1850.
Spotlight
How to think about Africa’s just energy transition
African nations are striving to boost their energy security, while also addressing climate change concerns such as flood risks and extreme heat.
This week, Carbon Brief speaks to the deputy Africa director of the Natural Resource Governance Institute, Ibrahima Aidara, on what a just energy transition means for the continent.
Carbon Brief: When African leaders talk about a “just energy transition”, what are they getting right? And what are they still avoiding?
Ibrahima Aidara: African leaders are right to insist that development and climate action must go together. Unlike high-income countries, Africa’s emissions are extremely low – less than 4% of global CO2 emissions – despite housing nearly 18% of the world’s population. Leaders are rightly emphasising universal energy access, industrialisation and job creation as non-negotiable elements of a just transition.
They are also correct to push back against a narrow narrative that treats Africa only as a supplier of raw materials for the global green economy. Initiatives such as the African Union’s Green Minerals Strategy show a growing recognition that value addition, regional integration and industrial policy must sit at the heart of the transition.
However, there are still important blind spots. First, the distributional impacts within countries are often avoided. Communities living near mines, power infrastructure or fossil-fuel assets frequently bear environmental and social costs without sharing in the benefits. For example, cobalt-producing communities in the Democratic Republic of the Congo, or lithium-affected communities in Zimbabwe and Ghana, still face displacement, inadequate compensation, pollution and weak consultation.
Second, governance gaps are sometimes downplayed. A just transition requires strong institutions (policies and regulatory), transparency and accountability. Without these, climate finance, mineral booms or energy investments risk reinforcing corruption and inequality.
Finally, leaders often avoid addressing the issue of who pays for the transition. Domestic budgets are already stretched, yet international climate finance – especially for adaptation, energy access and mineral governance – remains far below commitments. Justice cannot be achieved if African countries are asked to self-finance a global public good.
CB: Do African countries still have a legitimate case for developing new oil and gas projects, or has the energy transition fundamentally changed what ‘development’ looks like?
IA: The energy transition has fundamentally changed what development looks like and, with it, how African countries should approach oil and gas. On the one hand, more than 600 million Africans lack access to electricity and clean cooking remains out of reach for nearly one billion people. In countries such as Mozambique, Nigeria, Senegal and Tanzania, gas has been framed to expand power generation, reduce reliance on biomass and support industrial growth. For some contexts, limited and well-governed gas development can play a transitional role, particularly for domestic use.
On the other hand, the energy transition has dramatically altered the risks. Global demand uncertainty means new oil and gas projects risk becoming stranded assets. Financing is shrinking, with many development banks and private lenders exiting fossil fuels. Also, opportunity costs are rising; every dollar locked into long-lived fossil infrastructure is a dollar not invested in renewables, grids, storage or clean industry.
Crucially, development today is no longer just about exporting fuels. It is about building resilient, diversified economies. Countries such as Morocco and Kenya show that renewable energy, green industry and regional power trade can support growth without deepening fossil dependence.
So, the question is no longer whether African countries can develop new oil and gas projects, but whether doing so supports long-term development, domestic energy access and fiscal stability in a transitioning world – or whether it risks locking countries into an extractive model that benefits few and exposes countries to future shocks.
CB: What is the hardest truth about Africa’s energy transition that policymakers and international partners are still unwilling to confront?
IA: For me, the hardest truth is this: Africa cannot deliver a just energy transition on unfair global terms. Despite all the rhetoric, global rules still limit Africa’s policy space. Trade and investment agreements restrict local content, industrial policy and value-addition strategies. Climate finance remains fragmented and insufficient. And mineral supply chains are governed largely by consumer-country priorities, not producer-country development needs.
Another uncomfortable truth is that not every “green” investment is automatically just. Without strong safeguards, renewable energy projects and mineral extraction can repeat the same harms as fossil fuels: displacement, exclusion and environmental damage.
Finally, there is a reluctance to admit that speed alone is not success. A rushed transition that ignores governance, equity and institutions will fail politically and socially, and, ultimately, undermine climate goals.
If Africa’s transition is to succeed, international partners must accept African leadership, African priorities and African definitions of development, even when that challenges existing power dynamics in global energy and mineral markets.
Watch, read, listen
CRISIS INFLAMED: In the Brazilian newspaper Folha de São Paulo, columnist Marcelo Leite looked into the climate impact of extracting more oil from Venezuela.
BEYOND TALK: Two Harvard scholars argued in Climate Home News for COP presidencies to focus less on climate policy and more on global politics.
EU LEVIES: A video explainer from the Hindu unpacked what the EU’s carbon border tax means for India and global trade.
Coming up
- 10-12 January: 16th session of the IRENA Assembly, Abu Dhabi
- 13-15 January: Energy Security and Green Infrastructure Week, London
- 13-15 January: The World Future Energy Summit, Abu Dhabi
- 15 January: Uganda general elections
Pick of the jobs
- WRI Polsky Energy Center, global director | Salary: around £185,000. Location: Washington DC; the Hague, Netherlands; New Delhi, Mumbai, or Bengaluru, India; or London
- UK government Advanced Research and Invention Agency, strategic communications director – future proofing our climate and weather | Salary: £115,000. Location: London
- The Wildlife Trusts, head of climate and international policy | Salary: £50,000. Location: London
- Children’s Investment Fund Foundation, senior manager for climate | Salary: Unknown. Location: London, UK
DeBriefed is edited by Daisy Dunne. Please send any tips or feedback to debriefed@carbonbrief.org.
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The post DeBriefed 9 January 2026: US to exit global climate treaty; Venezuelan oil ‘uncertainty’; ‘Hardest truth’ for Africa’s energy transition appeared first on Carbon Brief.
The Trump administration in the US has announced its intention to withdraw from the UN’s landmark climate treaty, alongside 65 other international bodies that “no longer serve American interests”.
Every nation in the world has committed to tackling “dangerous anthropogenic interference with the climate system” under the 1992 UN Framework Convention on Climate Change (UNFCCC).
During Donald Trump’s second presidency, the US has already failed to meet a number of its UN climate treaty obligations, including reporting its emissions and funding the UNFCCC – and it has not attended recent climate summits.
However, pulling out of the UNFCCC would be an unprecedented step and would mark the latest move by the US to disavow global cooperation and climate action.
Among the other organisations the US plans to leave is the Intergovernmental Panel on Climate Change (IPCC), the UN body seen as the global authority on climate science.
In this article, Carbon Brief considers the implications of the US leaving these bodies, as well as the potential for it rejoining the UNFCCC in the future.
Carbon Brief has also spoken to experts about the contested legality of leaving the UNFCCC and what practical changes – if any – will result from the US departure.
- What is the process for pulling out of the UNFCCC?
- Is it legal for Trump to take the US out of the UNFCCC unilaterally?
- How could the US rejoin the UNFCCC and Paris Agreement?
- What changes when the US withdraws from the UNFCCC?
- What about the US withdrawal from the IPCC?
- What other organisations are affected?
What is the process for pulling out of the UNFCCC?
The Trump administration set out its intention to withdraw from the UNFCCC and the IPCC in a White House presidential memorandum issued on 7 January 2026.
It claims authority “vested in me as president by the constitution and laws of the US” to withdraw the country from the treaty, along with 65 other international and UN bodies.
However, the memo includes a caveat around its instructions, stating:
“For UN entities, withdrawal means ceasing participation in or funding to those entities to the extent permitted by law.”
(In an 8 January interview with the New York Times, Trump said he did not “need international law” and that his powers were constrained only by his “own morality”.)
The US is the first and only country in the world to announce it wants to withdraw from the UNFCCC.
The convention was adopted at the UN headquarters in New York in May 1992 and opened for signatures at the Rio Earth summit the following month. The US became the first industrialised nation to ratify the treaty that same year.
It was ultimately signed by every nation on Earth – making it one of the most ratified global treaties in history.
Article 25 of the treaty states that any party may withdraw by giving written notification to the “depositary”, which is elsewhere defined as being the UN secretary general – currently, António Guterres.
The article, shown below, adds that the withdrawal will come into force a year after a written notification is supplied.
The treaty adds that any party that withdraws from the convention shall be considered as also having left any related protocol.
The UNFCCC has two main protocols: the Kyoto Protocol of 1997 and the Paris Agreement of 2015.
Although former US president Bill Clinton signed the Kyoto Protocol in 1998, its formal ratification faced opposition from the Senate and the treaty was ultimately rejected by his successor, president George W Bush, in 2001.
Domestic opposition to the protocol centred around the exclusion of major developing countries, such as China and India, from emissions reduction measures.
The US did ratify the Paris Agreement, but Trump signed an executive order to take the nation out of the pact for a second time on his first resumed day in office in January 2025.
Is it legal for Trump to take the US out of the UNFCCC unilaterally?
Whether Trump can legally pull the US out of the UNFCCC without the consent of the Senate remains unclear.
The US previously left the Paris Agreement during Trump’s first term.
Both the UNFCCC and the Paris Agreement allow any party to withdraw with a year’s written notice. However, both treaties state that parties cannot withdraw within the first three years of ratification.
As such, the first Trump administration filed notice to exit the Paris Agreement in November 2019 and became the first nation in the world to formally leave a year later – the day after Democrat Joe Biden won the 2020 presidential election.
On his first day in office in 2021, Biden rejoined the Paris Agreement. This took 30 days from notifying the UNFCCC to come into force.
The legalities of leaving the UNFCCC are murkier, due to how it was adopted.
As Michael B Gerrard, director of the Sabin Center for Climate Change Law at Columbia Law School, explains to Carbon Brief, the Paris Agreement was ratified without Senate approval.
Article 2 of the US Constitution says presidents have the power to make or join treaties subject to the “advice and consent” of the Senate – including a two-thirds majority vote (see below).
However, Barack Obama took the position that, as the Paris Agreement “did not impose binding legal obligations on the US, it was not a treaty that required Senate ratification”, Gerrard tells Carbon Brief.
As noted in a post by Jake Schmidt, a senior strategic director at the environmental NGO Natural Resources Defense Council (NRDC), the US has other mechanisms for entering international agreements. It says the US has joined more than 90% of the international agreements it is party to through different mechanisms.
In contrast, George H Bush did submit the UNFCCC to the Senate in 1992, where it was unanimously ratified by a 92-0 vote, ahead of his signing it into law.
Reversing this is uncertain legal territory. Gerrard tells Carbon Brief:
“There is an open legal question whether a president can unilaterally withdraw the US from a Senate-ratified treaty. A case raising that question reached the US Supreme Court in 1979 (Goldwater vs Carter), but the Supreme Court ruled this was a political question not suitable for the courts.”
Unlike ratifying a treaty, the US Constitution does not explicitly specify whether the consent of the Senate is required to leave one.
This has created legal uncertainty around the process.
Given the lack of clarity on the legal precedent, some have suggested that, in practice, Trump can pull the US out of treaties unilaterally.
Sue Biniaz, former US principal deputy special envoy for climate and a key legal architect of the Paris Agreement, tells Carbon Brief:
“In terms of domestic law, while the Supreme Court has not spoken to this issue (it treated the issue as non-justifiable in the Goldwater v Carter case), it has been US practice, and the mainstream legal view, that the president may constitutionally withdraw unilaterally from a treaty, ie without going back to the Senate.”
Additionally, the potential for Congress to block the withdrawal from the UNFCCC and other treaties is unclear. When asked by Carbon Brief if it could play a role, Biniaz says:
“Theoretically, but politically unlikely, Congress could pass a law prohibiting the president from unilaterally withdrawing from the UNFCCC. (The 2024 NDAA contains such a provision with respect to NATO.) In such case, its constitutionality would likely be the subject of debate.”
How could the US rejoin the UNFCCC and Paris Agreement?
The US would be able to rejoin the UNFCCC in future, but experts disagree on how straightforward the process would be and whether it would require a political vote.
In addition to it being unclear whether a two-thirds “supermajority” vote in the Senate is required to leave a treaty, it is unclear whether rejoining would require a similar vote again – or if the original 1992 Senate consent would still hold.
Citing arguments set out by Prof Jean Galbraith of the University of Pennsylvania law school, Schmidt’s NRDC post says that a future president could rejoin the convention within 90 days of a formal decision, under the merit of the previous Senate approval.
Biniaz tells Carbon Brief that there are “multiple future pathways to rejoining”, adding:
“For example, Prof Jean Galbraith has persuasively laid out the view that the original Senate resolution of advice and consent with respect to the UNFCCC continues in effect and provides the legal authority for a future president to rejoin. Of course, the Senate could also give its advice and consent again. In any case, per Article 23 of the UNFCCC, it would enter into force for the US 90 days after the deposit of its instrument.”
Prof Oona Hathaway, an international law professor at Yale Law School, believes there is a “very strong case that a future president could rejoin the treaty without another Senate vote”.
She tells Carbon Brief that there is precedent for this based on US leaders quitting and rejoining global organisations in the past, explaining:
“The US joined the International Labour Organization in 1934. In 1975, the Ford administration unilaterally withdrew, and in 1980, the Carter administration rejoined without seeking congressional approval.
“Similarly, the US became a member of the United Nations Educational, Scientific and Cultural Organization (UNESCO) in 1946. In the 1980s, the Reagan administration unilaterally withdrew the US. The Bush administration rejoined UNESCO in 2002, but in 2019 the Trump administration once again withdrew. The Biden administration rejoined in 2023, and the Trump Administration announced its withdrawal again in 2025.”
But this “legal theory” of a future US president specifically re-entering the UNFCCC “based on the prior Senate ratification” has “never been tested in court”, Prof Gerrard from Columbia Law School tells Carbon Brief.
Dr Joanna Depledge, an expert on global climate negotiations and research fellow at the University of Cambridge, tells Carbon Brief:
“Due to the need for Senate ratification of the UNFCCC (in my interpretation), there is no way back now for the US into the climate treaties. But there is nothing to stop a future US president applying [the treaty] rules or – what is more important – adopting aggressive climate policy independently of them.”
If it were required, achieving Senate approval to rejoin the UNFCCC would take a “significant shift in US domestic politics”, public policy professor Thomas Hale from the University of Oxford notes on Bluesky.
Rejoining the Paris Agreement, on the other hand, is a simpler process that the US has already undertaken in recent years. (See: Is it legal for Trump to take the US out of the UNFCCC unilaterally?) Biniaz explains:
“In terms of the Paris Agreement, a party to that agreement must also be a party to the UNFCCC (Article 20). Assuming the US had rejoined the UNFCCC, it could rejoin the Paris Agreement as an executive agreement (as it did in early 2021). The agreement would enter into force for the US 30 days after the deposit of its instrument (Article 21).”
The Center for Climate and Energy Solutions, an environmental non-profit, explains that Senate approval was not required for Paris “because it elaborates an existing treaty” – the UNFCCC.
What changes when the US withdraws from the UNFCCC?
US withdrawal from the UNFCCC has been described in media coverage as a “massive hit” to global climate efforts that will “significantly limit” the treaty’s influence.
However, experts tell Carbon Brief that, as the Trump administration has already effectively withdrawn from most international climate activities, this latest move will make little difference.
Moreover, Depledge tells Carbon Brief that the international climate regime “will not collapse” as a result of US withdrawal. She says:
“International climate cooperation will not collapse because the UNFCCC has 195 members rather than 196. In a way, the climate treaties have already done their job. The world is already well advanced on the path to a lower-carbon future. Had the US left 10 years ago, it would have been a serious threat, but not today. China and other renewable energy giants will assert even more dominance.”
Depledge adds that while the “path to net-zero will be longer because of the drastic rollback of domestic climate policy in the US”, it “won’t be reversed”.
Technically, US departure from the UNFCCC would formally release it from certain obligations, including the need to report national emissions.
As the world’s second-largest annual emitter, this is potentially significant.
“The US withdrawal from the UNFCCC undoubtedly impacts on efforts to monitor and report global greenhouse gas emissions,” Dr William Lamb, a senior researcher at the Potsdam Institute for Climate Impact Research (PIK), tells Carbon Brief.
Lamb notes that while scientific bodies, such as the IPCC, often use third-party data, national inventories are still important. The US already failed to report its emissions data last year, in breach of its UNFCCC treaty obligations.
Robbie Andrew, senior researcher at Norwegian climate institute CICERO, says that it will currently be possible for third-party groups to “get pretty close” to the carbon dioxide (CO2) emissions estimates previously published by the US administration. However, he adds:
“The further question, though, is whether the EIA [US Energy Information Administration] will continue reporting all of the energy data they currently do. Will the White House decide that reporting flaring is woke? That even reporting coal consumption is an unnecessary burden on business? I suspect the energy sector would be extremely unhappy with changes to the EIA’s reporting, but there’s nothing at the moment that could guarantee anything at all in that regard.”
Andrew says that estimating CO2 emissions from energy is “relatively straightforward when you have detailed energy data”. In contrast, estimating CO2 emissions from agriculture, land use, land-use change and forestry, as well as other greenhouse gas emissions, is “far more difficult”.
The US Treasury has also announced that the US will withdraw from the UN’s Green Climate Fund (GCF) and give up its seat on the board, “in alignment” with its departure from the UNFCCC. The Trump administration had already cancelled $4bn of pledged funds for the GCF.
Another specific impact of US departure would be on the UNFCCC secretariat budget, which already faces a significant funding gap. US annual contributions typically make up around 22% of the body’s core budget, which comes from member states.
However, as with emissions data and GCF withdrawal, the Trump administration had previously indicated that the US would stop funding the UNFCCC.
In fact, billionaire and UN special climate envoy Michael Bloomberg has already committed, alongside other philanthropists, to making up the US shortfall.
Veteran French climate negotiator Paul Watkinson tells Carbon Brief:
“In some ways the US has already suspended its participation. It has already stopped paying its budget contributions, it sent no delegation to meetings in 2025. It is not going to do any reporting any longer – although most of that is now under the Paris Agreement. So whether it formally leaves the UNFCCC or not does not change what it is likely to do.”
Dr Joanna Depledge tells Carbon Brief that she agrees:
“This is symbolically and politically huge, but in practice it makes little difference, given that Trump had already announced total disengagement last year.”
The US has a history of either leaving or not joining major environmental treaties and organisations, such as the Paris Agreement and the Kyoto Protocol. (See: What is the process for pulling out of the UNFCCC?)
Dr Jennifer Allan, a global environmental politics researcher at Cardiff University, tells Carbon Brief:
“The US has always been an unreliable partner…Historically speaking, this is kind of more of the same.”
The NRDC’s Jake Schmidt tells Carbon Brief that he doubts US absence will lead to less progress at UN climate negotiations. He adds:
“[The] Trump team would have only messed things up, so not having them participate will probably actually lead to better outcomes.”
However, he acknowledges that “US non-participation over the long-term could be used by climate slow-walking countries as an excuse for inaction”.
Biniaz tells Carbon Brief that the absence of the US is unlikely to unlock reform of the UN climate process – and that it might make negotiations more difficult. She says:
“I don’t see the absence of the US as promoting reform of the COP process. While the US may have had strong views on certain topics, many other parties did as well, and there is unlikely to be agreement among them to move away from the consensus (or near consensus) decision-making process that currently prevails. In fact, the US has historically played quite a significant ‘broker’ role in the negotiations, which might actually make it more difficult for the remaining parties to reach agreement.”
After leaving the UNFCCC, the US would still be able to participate in UN climate talks as an observer, albeit with diminished influence. (It is worth noting that the US did not send a delegation to COP30 last year.)
There is still scope for the US to use its global power and influence to disrupt international climate processes from the outside.
For example, last year, the Trump administration threatened nations and negotiators with tariffs and withdrawn visa rights if they backed an International Maritime Organization (IMO) effort to cut shipping emissions. Ultimately, the measures were delayed due to a lack of consensus.
(Notably, the IMO is among the international bodies that the US has not pledged to leave.)
What about the US withdrawal from the IPCC?
As a scientific body, rather than a treaty, there is no formal mechanism for “withdrawing” from the IPCC. In its own words, the IPCC is an “organisation of governments that are members of the UN or World Meteorological Organization” (WMO).
Therefore, just being part of the UN or WMO means a country is eligible to participate in the IPCC. If a country no longer wishes to play a role in the IPCC, it can simply disengage from its activities – for example, by not attending plenary meetings, nominating authors or providing financial support.
This is exactly what the US government has been doing since last year.
Shortly before the IPCC’s plenary meeting for member governments – known as a “session” – in Hangzhou, China, in March 2025, reports emerged that US officials had been denied permission to attend.
In addition, the contract for the technical support unit for Working Group III (WG3) was terminated by its provider, NASA, which also eliminated the role of chief scientist – the position held by WG3 co-chair Dr Kate Cavlin.
(Each of the IPCC’s three “working groups” has a technical support unit, or TSU, which provides scientific and operational support. These are typically “co-located” between the home countries of a working group’s two co-chairs.)
The Hangzhou session was the first time that the US had missed a plenary since the IPCC was founded in 1988. It then missed another in Lima, Peru, in October 2025.
Although the US government did not nominate any authors for the IPCC’s seventh assessment cycle (AR7), US scientists were still put forward through other channels. Analysis by Carbon Brief shows that, across the three AR7 working group reports, 55 authors are affiliated with US institutions.
However, while IPCC authors are supported by their institutions – they are volunteers and so are not paid by the IPCC – their travel costs for meetings are typically covered by their country’s government. (For scientists from developing countries, there is financial support centrally from the IPCC.)
Prof Chris Field, co-chair of Working Group II during the IPCC’s fifth assessment (AR5), tells Carbon Brief that a “number of philanthropies have stepped up to facilitate participation by US authors not supported by the US government”.
The US Academic Alliance for the IPCC – a collaboration of US universities and research institutions formed last year to fill the gap left by the government – has been raising funds to support travel.
In a statement reacting to the US withdrawal, IPCC chair Prof Sir Jim Skea said that the panel’s focus remains on preparing the reports for AR7:
“The panel continues to make decisions by consensus among its member governments at its regular plenary sessions. Our attention remains firmly on the delivery of these reports.”
The various reports will be finalised, reviewed and approved in the coming years – a process that can continue without the US. As it stands, the US government will not have a say on the content and wording of these reports.
Field describes the US withdrawal as a “self-inflicted wound to US prestige and leadership” on climate change. He adds:
“I don’t have a crystal ball, but I hope that the US administration’s animosity toward climate change science will lead other countries to support the IPCC even more strongly. The IPCC is a global treasure.”
The University of Edinburgh’s Prof Gabi Hegerl, who has been involved in multiple IPCC reports, tells Carbon Brief:
“The contribution and influence of US scientists is presently reduced, but there are still a lot of enthusiastic scientists out there that contribute in any way they can even against difficult obstacles.”
On Twitter, Prof Jean-Pascal van Ypersele – IPCC vice-chair during AR5 – wrote that the US withdrawal was “deeply regrettable” and that to claim the IPCC’s work is contrary to US interests is “simply nonsensical”. He continued:
“Let us remember that the creation of the IPCC was facilitated in 1988 by an agreement between Ronald Reagan and Margaret Thatcher, who can hardly be described as ‘woke’. Climate and the environment are not a matter of ideology or political affiliation: they concern everyone.”
Van Ypersele added that while the IPCC will “continue its work in the service of all”, other countries “will have to compensate for the budgetary losses”.
The IPCC’s most recent budget figures show that the US did not make a contribution in 2025.
Carbon Brief analysis shows that the US has provided around 30% of all voluntary contributions in the IPCC’s history. Totalling approximately $67m (£50m), this is more than four times that of the next-largest direct contributor, the EU.
However, this is not the first time that the US has withdrawn funding from the IPCC. During Trump’s first term of office, his administration cut its contributions in 2017, with other countries stepping up their funding in response. The US subsequently resumed its contributions.
At its most recent meeting in Lima, Peru, in October 2025, the IPCC warned of an “accelerating decline” in the level of annual voluntary contributions from countries and other organisations, reported the Earth Negotiations Bulletin. As a result, the IPCC invited member countries to increase their donations “if possible”.
What other organisations are affected?
In addition to announcing his plan to withdraw the US from the UNFCCC and the IPCC, Trump also called for the nation’s departure from 16 other organisations related to climate change, biodiversity and clean energy.
These include:
- The Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) – the biodiversity equivalent of the IPCC.
- Intergovernmental Forum on Mining, Minerals, Metals and Sustainable Development – a voluntary group of more than 80 countries aiming to make the mining sector more sustainable.
- UN Energy – the principal UN organisation for international collaboration on energy.
- UN Oceans – a UN mechanism responsible for overseeing the International Seabed Authority (ISA) and other UN agencies related to ocean and coastal issues.
- UN Water – the UN agency responsible for water and sanitation.
- UN Collaborative Programme on Reducing Emissions from Deforestation and Forest Degradation in Developing Countries (UN-REDD) – a UN collaborative initiative for creating financial incentives for protecting forests.
- International Renewable Energy Agency – an intergovernmental organisation supporting countries in their transition to renewable energy.
- 24/7 Carbon-Free Energy Compact – a UN initiative launched in 2021 pushing governments, companies and organisations to achieve 100% low-carbon electricity generation.
- Commission for Environmental Cooperation – an organisation aimed at conserving North America’s natural environment.
- Inter-American Institute for Global Change Research – an intergovernmental organisation supported by 19 countries in North and South America for the support of planetary change research.
- International Energy Forum – an intergovernmental platform for dialogue among countries, industry and experts.
- International Solar Alliance – an organisation supporting the development of solar power and the phaseout of fossil fuels.
- International Tropical Timber Organization – an organisation aimed at protecting tropical forest resources.
- International Union for Conservation of Nature – an international nature conservation organisation and authority on the state of biodiversity loss.
- Renewable Energy Policy Network for the 21st Century – a global policy forum for renewable energy leadership.
- Secretariat of the Pacific Regional Environment Programme – a regional organisation aimed at protecting the Pacific’s environment.
As well as participating in the work of these organisations, the US is also a key source of funding for many of them – leaving their futures uncertain.
In a letter to members seen by Carbon Brief, IPBES chair and Kenyan ecologist, Dr David Obura, described Trump’s move as “deeply disappointing”.
He said that IPBES “has not yet received any formal notification” from the US, but “anticipates that the intention expressed to withdraw will mean that the US will soon cease to be a member of IPBES”, adding:
“The US is a founding member of IPBES and scientists, policymakers and stakeholders – including Indigenous peoples and local communities – from the US have been among the most engaged contributors to the work of IPBES since its establishment in 2012, making valuable contributions to objective science-based assessments of the state of the planet, for people and nature.
“The contribution of US experts ranges from leading landmark assessment reports, to presiding over negotiations, serving as authors and reviewers, as well as helping to steer the organisation both scientifically and administratively.”
Despite being a party to IPBES until now, the US has never been a signatory to the UN Convention on Biological Diversity (CBD), the nature equivalent of the UNFCCC.
It is one of only two nations not to sign the convention, with the other being the Holy See, representing the Vatican City.
The lack of US representation at the CBD has not prevented countries from reaching agreements. In 2022, countries gathered under the CBD adopted the Kunming-Montreal Global Biodiversity Framework, often described as the “Paris Agreement for nature”.
However, some observers have pointed to the lack of US involvement as one of the reasons why biodiversity loss has received less international attention than climate change.
The post Q&A: What Trump’s US exit from UNFCCC and IPCC could mean for climate action appeared first on Carbon Brief.
Q&A: What Trump’s US exit from UNFCCC and IPCC could mean for climate action
Greenhouse Gases
Analysis: World’s biggest historic polluter – the US – is pulling out of UN climate treaty
The US, which has announced plans to withdraw from the global climate treaty – the UN Framework Convention on Climate Change (UNFCCC) – is more historically responsible for climate change than any other country or group.
Carbon Brief analysis shows that the US has emitted a total of 542bn tonnes of carbon dioxide (GtCO2) since 1850, by burning fossil fuels, cutting down trees and other activities.
This is the largest contribution to the Earth’s warming climate by far, as shown in the figure below, with China’s 336GtCO2 significantly behind in second and Russia in third at 185GtCO2.
The US is responsible for more than a fifth of the 2,651GtCO2 that humans have pumped into the atmosphere between 1850 and 2025 as a result of fossil fuels, cement and land-use change.
China is responsible for another 13%, with the 27 nations of the EU making up another 12%.
In total, these cumulative emissions have used up more than 95% of the carbon budget for limiting global warming to 1.5C and are the predominant reason the Earth is already nearly 1.5C hotter than in pre-industrial times.
The US share of global warming is even more disproportionate when considering that its population of around 350 million people makes up just 4% of the global total.
On the basis of current populations, the US’s per-capita cumulative historical emissions are around 7 times higher than those for China, more than double the EU’s and 25 times those for India.
The US’s historical emissions of 542GtCO2 are larger than the combined total of the 133 countries with the lowest cumulative contributions, a list that includes Saudi Arabia, Spain and Nigeria. Collectively, these 133 countries have a population of more than 3 billion people.
See Carbon Brief’s previous detailed analysis of historical responsibility for climate change for more details on the data sources and methodology, as well as consumption-based emissions.
Additionally, in 2023, Carbon Brief published an article that looked at the “radical” impact of reassigning responsibility for historical emissions to colonial rulers in the past.
This approach has a very limited impact on the US, which became independent before the vast majority of its historical emissions had taken place.
The post Analysis: World’s biggest historic polluter – the US – is pulling out of UN climate treaty appeared first on Carbon Brief.
Analysis: World’s biggest historic polluter – the US – is pulling out of UN climate treaty
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