Global temperatures in the first quarter of 2025 were the second warmest on record, extending a remarkable run of exceptional warmth that began in July 2023.
This is despite weak La Niña conditions during the first two months of the year – which typically result in cooler temperatures.
With temperature data for the first three months of the year now available, Carbon Brief finds that 2025 is very likely to be one of the three warmest years on record.
However, it currently remains unlikely that temperatures in 2025 will set a new annual record.
In addition to near-record warmth, the start of 2025 has seen record-low sea ice cover in the Arctic between January and March – and the second-lowest minimum sea ice extent on record for Antarctica.
Second-warmest start to the year
In this quarterly state of the climate assessment, Carbon Brief analyses records from five different research groups that report global surface temperature records: NASA, NOAA, Met Office Hadley Centre/UEA, Berkeley Earth and Copernicus/ECMWF.
The figure below shows the annual temperatures from each of these groups since 1970, along with the average over the first three months of 2025.
(It is worth noting that the first three months may not be representative of the year as a whole, as greater historical warming rates mean that temperatures relative to pre-industrial levels tend to be larger in the northern hemispheric winter months of December, January and February.)
Annual global average surface temperatures from NASA GISTEMP, NOAA GlobalTemp, Hadley/UEA HadCRUT5, Berkeley Earth and Copernicus/ECMWF (lines), along with 2025 temperatures so far (January-March, coloured dots). Anomalies plotted with respect to the 1981-2010 period, and shown relative to pre-industrial based on the average pre-industrial temperatures in the Hadley/UEA, NOAA and Berkeley datasets that extend back to 1850. Chart by Carbon Brief.
Starting with this state of the climate update, Carbon Brief will be showing a World Meteorological Organization (WMO) aggregate of the five surface temperature records, rather than highlighting any particular one, reflecting a single best-estimate across the different groups.
The WMO aggregate is calculated by averaging the different records using a common 1981-2010 baseline period, before adding in the average warming since the pre-industrial period (1850-1900) across the datasets – NOAA, Hadley, and Berkeley – that extend back to 1850.
The figure below shows how global temperature so far in 2025 (black line) compares to each month in different years since 1940 (with lines coloured by the decade in which they occurred) in the WMO aggregate of surface temperature dataset.
Temperatures for each month from 1940 to 2025 from the WMO aggregate of temperature records. Anomalies plotted with respect to a 1850-1900 baseline. Chart by Carbon Brief.
The first three months of 2025 have been unusually warm, coming in in the top-three warmest on record across all the different scientific groups that report on global surface temperatures. This is despite the presence of moderate La Niña conditions in the tropical Pacific, which typically suppress global temperatures.
January 2025 was the warmest January on record in the WMO aggregate, February was the third warmest and March was tied with 2016 as the second warmest.
When combined, the first three months of the year in 2025 were the second-warmest Q1 period in the historical record, just 0.035C below the record set in 2024 after the peak of a strong El Niño event, as shown in the figure below.
Q1 temperature anomalies from 1850 through 2025 from the WMO aggregate of temperature records. Anomalies plotted with respect to a 1850-1900 baseline. Chart by Carbon Brief.
The persistence of warmth after the end of the 2023-24 El Niño event – and through a weak La Niña – has been highly unusual by historical standards. In most prior cases, global temperatures returned closer to the long-term temperature trend following the return to neutral El Niño Southern Oscillation (ENSO) conditions in the tropical Pacific.
Weak La Niña conditions have faded over the past month, with ENSO-neutral conditions returning and expected to persist for most models through the remainder of the year. However, predictions of ENSO status are particularly uncertain at this time of year due to a phenomenon known as the “spring predictability barrier”.
The figure below shows a range of different forecast models for the ENSO for the rest of this year, produced by different scientific groups. The values shown are sea surface temperature variations in the tropical Pacific – known as the El Niño 3.4 region – for overlapping three-month periods.
ENSO forecast models for overlapping three-month periods in the Niño3.4 region (January, February, March – JFM – and so on) for the remainder of 2025. Credit: Image provided by the International Research Institute for Climate and Society at Columbia Climate School.
On track to be a top-three warmest year
By looking at the relationship between the first three months and the annual temperatures for every year since 1970 – as well as ENSO conditions for the first three months of the year and the projected development of El Niño conditions for the remaining nine months – Carbon Brief has created a projection of what the final global average temperature for 2025 will likely be.
The analysis includes the estimated uncertainty in 2025 outcomes, given that temperatures from only the first quarter of the year are available so far.
The chart below shows the expected range of 2025 temperatures using the WMO aggregate – including a best-estimate (red) and year-to-date value (yellow). Temperatures are shown with respect to the pre-industrial baseline period (1850-1900).
Annual global average surface temperature anomalies from the WMO aggregate plotted with respect to a 1850-1900 baseline. To-date 2025 values include January-March. The estimated 2025 annual value is based on the relationship between the January-March temperatures and annual temperatures between 1970 and 2024. Chart by Carbon Brief.
Carbon Brief’s projection suggests that 2025 is virtually certain to be one of the top-three warmest years, with a best-estimate approximately equal to global temperatures in 2023.
However, this model assumes that 2025 follows the type of climate patterns seen in the past – patterns that were notably broken in 2023 – and to a lesser extent in 2024. Other recent estimates – such as one published by Berkeley Earth – give a higher probability of around 34% that 2025 will set a new temperature record.
The figure below shows Carbon Brief’s estimate of 2025 temperatures using the WMO aggregate, both at the beginning of the year and once each month’s data has come in. The estimate jumped notably after t2025 saw the warmest January on record, but has been relatively stable over the past three months.
Record-low Antarctic and Arctic sea ice
Both Arctic and Antarctic sea ice extent spent much of early 2025 at record, or near-record, lows.
The figure below shows both Arctic and Antarctic sea ice extent in 2025 (solid red and blue lines), the historical range in the record between 1979 and 2010 (shaded areas) and the record lows (dotted black line).
(Unlike global temperature records, which only report monthly averages, sea ice data is collected and updated on a daily basis, allowing sea ice extent to be viewed up to the present.)
Arctic and Antarctic daily sea ice extent from the US National Snow and Ice Data Center (NSIDC). The bold lines show daily 2025 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 sea ice saw a new record low nearly each day between January and March, recording a record-low winter peak extent in late March. Ice extent subsequently moved out of record-low territory in April.
It is worth noting that, as northern hemisphere winter conditions remain cold enough to refreeze sea ice, there tends to be less variability in extent year-to-year in the winter than in the summer, as the chart below illustrates.
Antarctic sea ice started the year within the historical range (1979-2010), before plunging to tie for the second-lowest minimum on record in late February. It has since recovered in April, and is currently on the low end of the historical range.
The post State of the climate: 2025 close behind 2024 as the hottest start to a year appeared first on Carbon Brief.
State of the climate: 2025 close behind 2024 as the hottest start to a year
Greenhouse Gases
Revealed: UK development body still has $700m invested overseas in fossil-fuel assets
British International Investment (BII), a UK government-owned and aid-funded company, has a portfolio of overseas fossil-fuel assets worth hundreds of millions of dollars, Carbon Brief can reveal.
In 2020, BII committed to “aligning” its “future” investments with the Paris Agreement and since then it has doubled its renewable-energy funding.
But, as of 2023, the last year for which data is available, it also still had a large portfolio of gas-fired power plants across Africa and south Asia.
Multiple freedom of information (FOI) requests by Carbon Brief reveal fossil-fuel energy and related projects worth nearly $700m (£526m) on BII’s books, which represents about 6% of its assets in 2023.
The FOI results also show that, at the end of last year, BII still had $70m (£53m) of unspent funds earmarked for foreign fossil-fuel companies in the coming years.
BII has not breached its own investment guidelines and says its fossil-fuel exposure fell further in 2024 as it aims to “manage and responsibly exit” these assets.
However, MPs and campaigners have criticised BII’s legacy fossil-fuel investments for “conflicting” with UK climate goals and diverting increasingly scarce aid resources.
Climate pledge
BII is the UK’s development finance institution (DFI), a publicly owned, for-profit company that invests in businesses in developing countries.
These investments are meant to promote economic development, especially via projects – including new energy infrastructure – deemed “too risky” for private investors.
BII largely supports itself using financial returns from its existing portfolio, which was worth approximately £7.3bn ($9.2bn) in 2023.
However, the UK government has also provided BII with billions of pounds from its aid budget. This support has grown even amid massive cuts to UK aid, with BII receiving an extra £400m last year due to reduced government spending on housing asylum seekers.
The government has also been leaning more on BII to reach its international climate finance goals.
Despite being wholly owned – and partly funded – by the Foreign, Commonwealth and Development Office (FCDO), BII has an “arm’s length” relationship with the UK government and makes its own investment decisions.
In 2020, the previous Conservative government committed the UK to ending new overseas fossil-fuel funding beyond March 2021.
This came after BII – then known as CDC Group – had pledged in its 2020 climate strategy that it would not make any new investments that were “misaligned with the Paris Agreement”, based on a Task Force on Climate-related Financial Disclosures framework.
Then-chief executive Nick O’Donohoe stated that the climate strategy would “shape every single investment decision we make moving forward”.
This was hailed as an end to fossil-fuel financing by the institution, despite some remaining “loopholes”. Notably, its fossil-fuel policy allowed for new investments in gas projects if they were deemed “consistent with a country’s pathway to net-zero by 2050”.
Since making its pledge, BII has repeatedly come under fire from MPs and campaigners for continuing to hold “active investments” in fossil-fuel companies.
Fossil assets
BII says that its fossil-fuel portfolio, which mainly consists of gas-fired power plants in “power-constrained” African nations, “has been on a steady downward trajectory since 2020”.
However, the company has not released data on the value of its fossil-fuel assets since 2021, citing “commercial sensitivities”.
In September 2024, Carbon Brief filed an FOI request with BII to obtain data on the company’s fossil-fuel and renewable-energy investments, as well as their asset value.
Following more than six months of back-and-forth – including Carbon Brief requesting an internal review of its FOI request – the company provided much of the information that was originally requested at the end of March 2025.
This included annual data on projects that BII has already committed to support, such as the Sirajganj 4 gas plant in Bangladesh and the Amandi Energy gas plant in Ghana.
As the chart below shows, BII’s cumulative commitments to fossil-fuel companies have remained roughly the same since its climate strategy in 2020. This is in line with its pledge to provide no “new commitments” to most fossil-fuel projects.
One exception is an extra $20m (£15m) in 2021 for Globeleq, a company controlled by BII that primarily supports gas power in Africa. An investment in a Mozambique gas project that year by Globeleq was deemed “Paris-aligned” and, therefore, allowed under BII’s rules.
Meanwhile, BII’s total commitments to renewable energy projects have more than doubled, from $894m (£672m) to $2.1bn (£1.6bn), between 2020 and 2024.
Once funds have been “committed”, they can remain “undrawn” for many years. This means that money committed before 2020 can still be distributed without breaching BII’s pledge. Carbon Brief asked BII how much of these “commitments” remained undrawn each year.
This revealed that BII has continued sending money to fossil-fuel projects since its 2020 pledge, disbursing around $57m (£43m) over this period. At the end of 2024, there was still $67m (£50m) of “undrawn” fossil-fuel finance waiting to be spent.
BII tells Carbon Brief that, as “commitments” are legal contracts, it is obliged to provide these funds as and when they are required.
Beyond “direct” investments in energy projects, BII has also made “indirect” commitments to fossil fuels via private financial institutions. The company tells Carbon Brief it does not have details of how much these third-party funds invest in fossil-fuel projects.
Daniel Willis, finance campaign manager at the NGO Recourse, points to examples such as Gigajoule and Ademat, companies that have received new finance injections for fossil-fuel projects beyond the 2020 date, on BII’s behalf. (Again, this is allowed under BII’s guidelines.)
Willis tells Carbon Brief that these investments and the continued payments from existing commitments “clearly go against the spirit of the UK government’s fossil fuel policy”.
BII initially rejected Carbon Brief’s request for the “net asset value” of every fossil-fuel investment in its portfolio. It argued that disclosure could weaken its commercial position.
However, the company eventually agreed to disclose the aggregate value of its fossil-fuel assets for the period 2020-2023.
The data reveals that, as of 2023, BII still owned $591m (£444m) worth of gas-fired power plants and other fossil-fuel energy assets, rising to $676m (£508m) when indirect assets are included. This amounts to around 6% of BII’s assets.
While BII declined to provide Carbon Brief with the 2024 figures, a company spokesperson tells Carbon Brief that they plan to release them “this summer”, adding:
“Our 2024 annual report and accounts…will show that our exposure to fossil-fuels assets has fallen 39% since 2020 and now makes up just 6% of our total portfolio. Over the same period, the value of our climate-finance portfolio has increased by 122% to $2.5bn [£1.9bn] and now accounts for 26% of our total portfolio.”
As the chart below shows, there has already been a gradual drop in the value of BII’s direct fossil-fuel energy investments since 2020. The decline can likely be attributed to investees paying off debts to BII, fossil-fuel assets losing value and – to some extent – BII exiting smaller investments.
With evidence that BII’s fossil-fuel portfolio is declining in value, Sandra Martinsone, policy manager at the international development network Bond, tells Carbon Brief that “sooner or later” these will likely become stranded assets:
“The longer BII holds on to these fossil-fuel investments, the higher the risk of losing the invested aid pounds.”
The drop in the value of BII’s indirect fossil-fuel and “other carbon-related” assets – which includes non-energy companies that serve fossil-fuel companies – has been sharper. This can be largely attributed to BII ending support for fossil-fuel trade and supply chains in 2022.
‘Worrying trajectory’
In its FOI response, BII says that it “seeks to manage and responsibly exit fossil-fuel assets”. However, NGOs and politicians have raised concerns about the pace of change.
Natalie Jones, a policy advisor specialising in fossil-fuel phaseout at the International Institute for Sustainable Development (IISD), tells Carbon Brief that while BII has not breached its own climate guidelines:
“The fact that fossil fuel investments remain on BII’s books is not a good look for the organisation, bearing in mind its 2020 commitment to aligning its activities and investments with the Paris Agreement and the UK’s 2021 policy to end all international public support for fossil fuels.”
Civil-society groups have repeatedly called for BII to set a timeline for divesting from fossil fuels. They have even argued that, in the context of “drastic” UK aid cuts, BII should not receive more aid funding and instead reinvest funds from some of its existing assets.
Criticism of BII’s approach to fossil fuels is captured in a 2023 report by the International Development Committee of MPs. It refers to BII legacy investments “conflicting” with UK policies, including the alignment of all aid with the Paris Agreement.
The report also notes that there “does not appear to be a definitive path for BII exiting those fossil-fuel investments or transitioning its existing investment portfolio to green energy”.
Committee chair and Labour MP, Sarah Champion, says that, while the most recent data is not yet publicly available, the figures released to Carbon Brief point to a “worrying trajectory” in BII’s fossil-fuel investments. She tells Carbon Brief:
“It appears that BII has stayed on this worrying trajectory. This must change: as the government proposes a new strategic direction for UK aid spending, focusing on poverty reduction and genuinely responsible investment must be BII’s number one priority.”
In a statement alongside its FOI response, BII says that “forced divestment increases the likelihood that buyers of such assets would be less responsible owners, thereby increasing the future risk of negative climate impact”.
It also says that “being viewed as a forced seller” could reduce the value BII could obtain from those assets. This position was supported by the previous Conservative government.
Jones tells Carbon Brief that concerns about the responsibility of new owners are legitimate:
“However, it would be great to see from BII a plan to responsibly exit or, even better, decommission their fossil fuel assets. There is a case to be made for a responsible exit that would free up funds for much-needed climate finance.”
BII argues that, with around 600 million Africans still lacking access to electricity, gas power remains “essential” for providing “baseload” power to many nations on the continent.
This position has been supported by a number of African governments. However, many civil-society groups, both in Africa and around the world, argue that developed countries should focus financial resources on expanding clean power capacity in developing countries.
Nick Dearden, director of Global Justice Now, which has previously questioned the legality of the BII-controlled Globeleq supporting gas power in Africa, tells Carbon Brief it is “inappropriate” for aid money to be spent this way:
“It’s also trapping the countries that are building this stuff into a type of energy which is on its way out.”
The post Revealed: UK development body still has $700m invested overseas in fossil-fuel assets appeared first on Carbon Brief.
Revealed: UK development body still has $700m invested overseas in fossil-fuel assets
Greenhouse Gases
DeBriefed 16 May 2025: Has China’s CO2 peaked?; US bill ‘would kill IRA’; Poland’s coal collapse
Welcome to Carbon Brief’s DeBriefed.
An essential guide to the week’s key developments relating to climate change.
This week
US budget bill ‘would kill IRA’
WAYS AND MEANS: The future of Joe Biden’s signature climate policy, the Inflation Reduction Act (IRA), is in doubt after Republicans on two key Congressional committees passed budget proposals that “would effectively kill” it, reported Heatmap News. The proposals would end clean-energy tax credits and rebates for electric vehicle (EV) purchases, “claw back” climate grants and “slash” related spending, said Reuters.
DEFENCE DOUBTS: While a “small subset” of House Republicans have been trying to defend the IRA, it is unclear if they would block passage of the wider budget bill to get their way, according to E&E News. In the Senate, Politico said “some” Republicans are “pushing back” on the current proposals. A New York Times feature said Republican districts “have the most to lose” if all of the IRA tax credits are repealed. Semafor reported Republicans were “wrestling with possible failure” of the bill, in the face of opposition from Democrats and their own ranks. (Law firm Grant Thornton said policymakers were hoping to pass the bill by 4 July.)
SOCIAL COST: Meanwhile, a new White House memo directed US government agencies to disregard economic damages from climate change, reported E&E News. Under a headline asking, “What’s the cost of pollution? Trump says zero”, the New York Times explained that the “social cost of carbon” had been used for more than two decades to help weigh the costs and benefits of federal policies and regulations. It said the move could face legal challenges.
Around the world
- DOWNPOUR DEATHS: More than 100 people were killed by floods in the Democratic Republic of the Congo, Agence-France Presse reported. Extreme rainfall also killed at least seven people in Somalia, the Associated Press said.
- PARIS PERIL: A UK opposition minister falsely attacked climate science and said his party could exit the Paris Agreement if elected, the Guardian said. The Guardian also reported on how Australia’s new opposition leader “could abandon net-zero”.
- GERMAN GAS: New economy minister Katharina Reiche wants more gas-fired power plants, according to Die Zeit. The country’s climate council warned the new government’s plans could breach climate goals, said Clean Energy Wire.
- DENGUE DANGER: Colombia’s El Espectador reported on rising climate-driven risks from dengue fever in Brazil, Costa Rica, Ecuador, Mexico and Panama.
- COP30 CREW: The Brazilian COP30 presidency has appointed 30 envoys, including “key liaisons” for strategic regions such as China’s Xie Zhenhua, Jonathan Pershing from the US and former UNFCCC chief Patricia Espinosa, Climate Home News said.
60%
The yearly rise in EV sales in emerging markets in Asia and Latin America in 2024, according to new data from the International Energy Agency.
Latest climate research
- Even passing 1.5C of global warming temporarily would trigger a “significant” risk of Amazon forest “dieback”, said research covered by Carbon Brief.
- Rapidly rising emissions from China’s agricultural machinery could “hinder” the country’s push towards net-zero, according to a study covered by Carbon Brief.
- Findings in Environmental Research Letters found that the benefits of CO2 “fertilisation” on forests are likely to be constrained by warming.
(For more, see Carbon Brief’s in-depth daily summaries of the top climate news stories on Monday, Tuesday, Wednesday, Thursday and Friday.)
Captured
For the first time on record, China’s CO2 emissions have fallen as a result of clean energy expansion rather than weak growth in electricity demand, according to new analysis for Carbon Brief. The analysis, which has been covered by outlets including AFP, Semafor and the New York Times, found that China’s emissions from fossil fuels and cement fell 1.6% in the first quarter of 2025 and are now 1% below the peak reached in March 2024. The months ahead will be critical for what comes next, as Beijing is working to finalise its next international climate pledge for 2035 and its five-year plan for 2026-2030.
Spotlight
How Poland started speeding away from coal power
This week, Carbon Brief reports on coal falling to barely half of Poland’s power supplies.
The first round of Poland’s presidential election is on Sunday and Rafał Trzaskowski, from prime minister Donald Tusk’s centre-right party Civic Platform, is favoured to win.
Long seen as one of the world’s most coal-reliant countries, Poland’s electricity system is in the midst of dramatic and increasingly rapid change.
When Poland joined the EU in 2004, coal-fired power stations supplied 93% of the country’s electricity. Coal accounted for more than three-quarters of the total as recently as 2018, the year the country hosted COP24 in Katowice.
Since then, a gradual shuffle away from coal has turned to a sprint.
In 2024, coal generated little more than half of Poland’s electricity, according to data from thinktank Ember – and a coal power phaseout by 2035 is now seen as a realistic prospect.
While the topic has not played a big role in the election campaign, there is now broad public acceptance that “coal is over in Poland”, said Joanna Maćkowiak-Pandera, president of Polish thinktank Forum Energii. She told Carbon Brief:
“The extreme rightwing tries to claim that coal is the future and there is coal for [another] 400 years…[But] even the coal-mining sector does not believe it.”
As of 2024, coal contributed just 53.5% of electricity generation in Poland, with wind and solar making up 23.5%, gas power 12.1% and other renewables another 6.3%.
Coal ‘death spiral’
The “death spiral” for coal power is due to the high cost of coal mining in Poland, the old age of coal power plants, pressure from climate policies such as the EU emissions trading system (EUETS) and a loss of market share to renewables, said Maćkowiak-Pandera:
“You can be pro-coal, but you will not change the economics, physics, geology and the reality of the financial market.”
Until 2023, the right-wing Law and Justice party (PiS) had held the reins of government, having won the 2015 election after promising to protect the coal industry.
Following power cuts that summer, however, PiS increasingly accepted that renewbles – particularly solar power – could support energy security, explained Maćkowiak-Pandera.
(Renewables enjoy broad public support and are associated with energy security, she said.)
With backing from government policy, Poland’s solar capacity leapt from just 200 megawatts in 2015 to more than 20 gigawatts in 2024 – a 100-fold increase.
Still, PiS strongly resisted calls to phase out coal. In 2020, it struck a deal with unions to subsidise the Polish coal-mining industry until 2049. The subsidies remain in place.
After winning parliamentary elections in 2023, Tusk promised a “much faster energy transition” based on renewables and nuclear power, said Maćkowiak-Pandera.
While utility firms would “really love” to phase out coal plants within as little as three to five years, there is a growing consensus around 2035 as a more achievable end date, she said:
“It’s really not controversial any more…I speak with politicians, with utilities, with [electricity] transmission system operators, even with miners. Everybody is aware of the situation.”
Instead, there is a practical conversation around how best to replace coal at the lowest cost, explained Maćkowiak-Pandera.
This will mean more renewables, but also the flexible capacity needed to manage the grid – including some new gas-fired power plants – as well as energy storage and market reforms, she said.
Poland’s rapid transition may not have made many headlines, but other major coal-burning countries are starting to pay attention.
Maćkowiak-Pandera has welcomed delegations from China, South Africa, Mexico and Brazil, eager to learn about Poland’s experience. She added:
“For Chinese partners, it’s interesting because they like [our] pragmatic approach…they like that Poland [is] sometimes not mentioning climate, [but] is doing it anyhow.”
Watch, read, listen
CHINESE CROWING: A widely shared blog post on nationalist media outlet Guancha said China was taking climate action to “win the future energy revolution” and, among other things, to “save at least $600bn” on imported oil by shifting to EVs.
‘RUNNING BLIND’: For the Bulletin of Atomic Scientists, climate scientist Peter Gleick said the Trump administration’s “purges” of climate research were “threats to national security”.
‘REALISM’ REJECTED: The Wicked Problems podcast discussed the “defeatism” behind a recent initiative calling for “climate realism”, as well as the “abundance agenda”.
Coming up
- 18 May: Poland presidential election
- 19 May: EU-UK summit, London
- 19-23 May: First UN climate week 2025, Panama City, Panama
- 19-27 May: World Health Assembly 2025, Geneva, Switzerland
Pick of the jobs
- European Commission, programme manager (climate change and sustainable energy) | Salary: Unknown. Location: Brussels, Belgium
- Dialogue Earth, southeast Asia editor | Salary: £43,370. Location: London
- Royal Botanic Gardens Kew, postdoctoral research associate in genomics and climate change | Salary: £43,751. Location: London
DeBriefed is edited by Daisy Dunne. Please send any tips or feedback to debriefed@carbonbrief.org.
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The post DeBriefed 16 May 2025: Has China’s CO2 peaked?; US bill ‘would kill IRA’; Poland’s coal collapse appeared first on Carbon Brief.
DeBriefed 16 May 2025: Has China’s CO2 peaked?; US bill ‘would kill IRA’; Poland’s coal collapse
Even passing 1.5C of global warming temporarily would trigger a “significant” risk of Amazon forest “dieback”, says a new study.
Dieback would see large numbers of trees die, shifting the lush rainforest into a dry savannah.
The research, published in Nature Climate Change, assesses the impact of “overshooting” the aspirational goal of the Paris Agreement on the Amazon and Siberian forests.
Overshoot would see warming surpass 1.5C above pre-industrial levels in the coming decades, before being brought back down before 2100 through large-scale carbon dioxide removal.
Using hundreds of climate-model simulations, the authors assess the influence of the “sensitivity” of the climate – a measure of the planet’s temperature response to a given increase in atmospheric CO2.
Across all simulations where global warming in 2100 surpasses 1.5C, 37% show “some amount of dieback”, the study says.
However, the risk increases further in the long term, with “55% of simulations exhibiting dieback by 2300”.
One author tells Carbon Brief that the study highlights that overshooting 1.5C leaves forest ecosystems “exposed to more risk than [they] need to be”.
The findings show that “we can’t afford complacency”, he warns.
Warming pathways
As the planet warms, there is an increasing risk that parts of the Earth system will cross “tipping points” – critical thresholds that, if exceeded, could push a system into an entirely new state.
For example, a seminal 2022 study warned that five tipping elements – including the collapse of the West Antarctic ice sheet and abrupt permafrost thaw – are already within reach, while others are becoming increasingly more likely as temperatures rise.
One way to limit warming to 1.5C by the end of the century involves initially overshooting the threshold. However, research published last year warns that the longer the 1.5C threshold is breached – and the higher the peak temperature – the greater the risk of crossing tipping points.
The new study uses modelling to investigate the risks of overshoot for the Amazon and Siberian forests.
The paper considers three illustrative mitigation pathways taken from the Intergovernmental Panel on Climate Change’s (IPCC) mitigation report from its sixth assessment cycle, which was published in 2022.
Gregory Munday is an applied scientist at the UK Met Office Hadley Centre and lead author on the study. He tells Carbon brief that the authors selected “optimistic” pathways that “each have different relationships to the Paris Agreement goals”.
For each scenario, the authors assess a range of different climate sensitivities – a measure of the planet’s temperature response to a given increase in atmospheric CO2. The average outcome of each pathway is:
- The “renewables” scenario shows a future with reduced emissions and a heavy reliance on renewable energy, which keeps warming below 1.5C by 2100.
- The “negative emissions” pathway shows a world in which warming initially overshoots the 1.5C threshold, but extensive use of carbon removal sees warming drop back below 1.5C before 2100.
- The “gradual strengthening” pathway illustrates a strengthening of climate policies implemented in 2020, with rapid reductions mid-century and a reliance on net-negative emissions by the end of this century. This pathway sees global average temperatures reach 1.8C by 2100.
The authors run the emissions pathways through a simple climate “emulator” model, which calculates the global temperatures associated with each emission pathway.
The charts below show cumulative CO2 emissions (left), atmospheric CO2 concentration (middle) and changes in global average surface temperature compared to the pre-industrial level (right), for the renewables (green), negative emissions (purple) and gradual strengthening (yellow) pathways until the year 2300.
The authors then use a different modelling framework to project the impacts of each emissions scenario.
Study author Dr Chris Jones leads the UK Met Office Hadley Centre’s research into vegetation and carbon cycle modelling and their interactions with climate. He tells Carbon Brief that the new study is the first application of this modelling framework, which he describes as a “rapid response tool”.
He says the tool was developed to “rapidly look at a range of climate outcomes, both global and local, for new scenarios”, adding that it provides a “pretty good approximation” of what traditional global climate models would do.
Munday adds that the framework is able to produce results within days or weeks, rather than taking “months and months”.
Finally, the authors use land surface model JULES to assess forest health under the different scenarios. Overall, the authors produce 918 simulations each of Amazon and Siberian forest health.
Forest health
The authors assess forest health using two metrics. The first is the forest growth metric “net primary productivity”, a measure of the rate that energy is stored as biomass by plants, which can indicate forest productivity. The second metric, forest cover, is a way of measuring the forest’s long-term response.
The models show that rising CO2 levels causes net primary productivity to increase, due to the CO2 fertilisation effect, driving more rapid forest growth. Conversely, many of the impacts of climate change, such as increased heat and changes to rainfall patterns, can be detrimental to forests, damaging or killing trees.
To identify the impacts of overshooting 1.5C on the Amazon and Siberian forests, the authors compare the “renewables” and “negative emissions” pathways. Both of these scenarios reach a similar global average temperature by the year 2100, but the former does so without overshoot, while the latter overshoots 1.5C before temperatures come back down.
The maps below show the difference in net primary productivity in the Amazon (left) and Siberian forests (right) between the two scenarios in the year 2100. Brown shading indicates that net primary productivity was higher in the non-overshoot scenario, while blue indicates that it was higher in the overshoot scenario.
The maps show that “large areas of both Amazonian and Siberian forest show reduced net primary productivity” by 2100 due to overshoot, compared to a scenario with no overshoot, the paper says.
‘High-risk zones’
From the three pathways, the authors generate 918 simulations of future climate and corresponding Amazon forest health.
The authors use these results to identify which future temperature and rainfall conditions result in net forest “dieback”. This is when large numbers of trees die, shifting the rainforest into a dry savannah.
The plots below show which simulations result in Amazon dieback by the year 2100 (left) and 2300 (right), for different amounts of rainfall and temperature levels in the year 2100. Each graph is divided into four sections – hot and wet (top right), hot and dry (bottom right), cold and wet (top right) and cold and dry (bottom right). These sections are based on average regional temperature and rainfall in the year 2100.
Coloured dots indicate scenarios that see forest dieback. These are coloured by pathway, for renewables (green), negative emissions (purple) and gradual strengthening (yellow). Grey dots indicate scenarios without Amazon dieback. The red lines indicate “high-risk climatic zones”, above which there is “a significant risk of dieback”.
The study finds that most Amazon dieback scenarios happen in hot, dry conditions, the authors note.
Across all simulations where warming in 2100 is above 1.5C, 37% show “some amount of dieback” the study says. However, in these model runs, the risk increases further in the long term, the study notes, with “55% of simulations exhibiting dieback by 2300”.
Prof Nico Wunderling is a professor of computational Earth system science at the Potsdam Institute for Climate Impact Research and was not involved in the new research. He tells Carbon Brief it is significant that, according to this study, the Amazon will face impacts from climate change below the tipping point threshold of 2-6C, as assessed in the landmark 2022 tipping points paper.
The authors also carry out this analysis for Siberian forests. Instead of a drop in tree cover, they find a change in the composition of trees. Munday tells Carbon Brief that the vegetation shifts “from grassy surface types to lots more trees and shrubs” in a process called “woody encroachment”.
Woody encroachment can have significant negative impacts on terrestrial carbon sequestration, the hydrological cycle and local biodiversity.
“The Siberian forest is probably committed to a long-term, and possibly substantial, expansion of tree cover,” the authors write.
High-risk scenarios
The greatest uncertainty in this study comes from the spread of climate sensitivities, Munday tells Carbon Brief.
He elaborates:
“This means that although we simulate the impacts from extremely optimistic mitigation scenarios, there is a chance that the Earth’s climate sensitivity is much higher than we expect, and so, small but significant risks of short- and long-term forest ecosystem impacts exist in spite of the choice of these strong-mitigation scenarios.”
In other words, if climate sensitivity is higher than expected, forests could face harmful impacts even under low emissions scenarios.
Dr David McKay – a lecturer in geography, climate change and society at the University of Sussex – is the lead author of the 2022 study. He tells Carbon Brief that the new paper “shows the value in focusing not just on model averages, but also exploring a wide range of possible futures to capture potential ‘low probability, high impact’ outcomes”. He adds:
“[The study shows] how negative emissions to reduce warming might help restabilise these forests in future if we do overshoot 1.5C, but as such large-scale CO2 removal remains hypothetical, we shouldn’t assume we can rely on this in practice.”
However, McKay also notes some uncertainties in the models used. Mckay tells Carbon Brief that the vegetation model used in this study doesn’t include fire and “has some limitations around soil moisture stress and vegetation in the tundra”. These are “likely important for resolving potential tipping points in these biomes”.
Therefore, he adds, the study “doesn’t show how regional tipping points could potentially further amplify and lock-in these future forest shifts, even with negative emissions”.
Dr David Lapola is researcher at the University of Campinas in Brazil and was not involved in the study. He also warns that vegetation models provide a “poor representation of how CO2 may affect these forests directly”. Lapola argues that scientists must “collect field data to make any new advancement with models”.
Nevertheless, Lapola tells Carbon Brief that studies such as this will be “extremely useful” for the IPCC’s upcoming seventh assessment cycle, which will include a dedicated chapter on tipping points and other “low-likelihood high impact events” for the first time.
Study author Jones tells Carbon Brief that overshooting 1.5C leaves forest ecosystems “exposed to more risk than [they] need to be”. The findings show that “we can’t afford complacency”, he warns.
The post ‘Significant’ risk of Amazon forest dieback if global warming overshoots 1.5C appeared first on Carbon Brief.
‘Significant’ risk of Amazon forest dieback if global warming overshoots 1.5C
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