The year 2025 saw the return to power of Donald Trump, a jewellery heist at the Louvre museum in Paris and an engagement that “broke the internet”.
Amid the biggest stories of the year, climate change research continued to feature prominently in news and social media feeds.
Using data from Altmetric, which scores research papers according to the attention they receive online, Carbon Brief has compiled its annual list of the 25 most talked-about climate-related studies of the past year.
The top 10 – shown in the infographic above and list below – include research into declining butterflies, heat-related deaths, sugar intake and the massive loss of ice from the world’s glaciers:
- Indicators of Global Climate Change 2024: annual update of key indicators of the state of the climate system and human influence
- Rapid butterfly declines across the US during the 21st century
- Global warming has accelerated: Are the UN and the public well informed?
- Community estimate of global glacier mass changes from 2000 to 2023
- The EAT-Lancet Commission on healthy, sustainable and just food systems
- Carbon majors and the scientific case for climate liability
- Estimating future heat-related and cold-related mortality under climate change, demographic and adaptation scenarios in 854 European cities
- Systematic attribution of heatwaves to the emissions of carbon majors
- Ambient outdoor heat and accelerated epigenetic aging among older adults in the US
- Rising temperatures increase added sugar intake disproportionately in disadvantaged groups in the US
Later in this article, Carbon Brief looks at the rest of the top 25 and provides analysis of the most featured journals, as well as the gender diversity and country of origin of authors.
New for this year is the inclusion of Altmetric’s new “sentiment analysis”, which scores how positive or negative a paper’s social media attention has been.
(For Carbon Brief’s previous Altmetric articles, see the links for 2024, 2023, 2022, 2021, 2020, 2019, 2018, 2017, 2016 and 2015.)
Global indicators
The top-scoring climate paper of 2025, ranking 24th of any research paper on any topic, is the annual update of the “Indicators of Global Climate Change” (IGCC) report.
The report was established in 2023 to help fill the gap in climate information between assessments of the Intergovernmental Panel on Climate Change (IPCC), which can take up to seven years to complete. It includes the latest data on global temperatures, the remaining carbon budget, greenhouse gas emissions and – for the first time – sea level rise.
The paper, published in Earth System Science Data, has an Altmetric score of 4,099. This makes it the lowest top-scoring climate paper in Carbon Brief’s list since 2017.
(An Altmetric score combines the mentions that published peer-reviewed research has received from online news articles, blogs, Wikipedia and on social media platforms such as Facebook, Reddit, Twitter and Bluesky. See an earlier Carbon Brief article for more on how Altmetric’s scoring system works.)
Previous editions of the IGCC have also appeared in Carbon Brief’s list – the 2024 and 2023 iterations ranked 17th and 18th, respectively.
This year’s paper was mentioned 556 times in online news stories, including in the Associated Press, Guardian, Independent, Hill and BBC News.
Many outlets led their coverage with the study’s findings on the global “carbon budget”. This warned that the remaining carbon budget to limit warming to 1.5C will be exhausted in just three years if global emissions continue at their current rate.
In a Carbon Brief guest post about the study, authors Prof Piers Forster and Dr Debbie Rosen from the University of Leeds wrote:
“It is also now inevitable that global temperatures will reach 1.5C of long-term warming in the next few years unless society takes drastic, transformative action…Every year of delay brings reaching 1.5C – or even higher temperatures – closer.”
Forster, who was awarded a CBE in the 2026 new year honours list, tells Carbon Brief that media coverage of the study was “great” at “putting recent extreme weather in the context of rapid long-term rates of global warming”.
However, he adds:
“Climate stories are not getting the coverage they deserve or need at the moment so the community needs to get all the help we can for getting clear consistent messages out there.”
The paper was tweeted more than 300 times and posted on Bluesky more than 950 times. It also appeared in 22 blogs.
Using AI, Altmetric now analyses the “sentiment” of this social media attention. As the summary figure below shows, the posts about this paper were largely positive, with an approximate 3:1 split of positive and negative attention.
Butterfly decline
With an Altmetric score of 3,828, the second-highest scoring climate paper warns of “widespread” declines in butterfly numbers across the US since the turn of the century.
The paper, titled “Rapid butterfly declines across the US during the 21st century” and published in Science, identifies a 22% fall in butterfly numbers across more than 500 species between 2000 and 2020.
(There is a higher-scoring paper, “The 2025 state of the climate report: a planet on the brink”, in the journal BioScience, but it is a “special report” and was not formally peer reviewed.)
The scale of the decline suggests “multiple and broadly acting threats, including habitat loss, climate change and pesticide use”, the paper says. The authors find that “species generally had stronger declines in more southerly parts of their ranges”, with some of the most negative trends in the driest and “most rapidly warming” US states.
The research was covered in 560 news articles, including the New York Times, Guardian, Associated Press, NPR, El País and BBC News. Much of the news coverage led with the 22% decline figure.
The paper was also mentioned in 13 blogs, more than 750 Bluesky posts and more than 600 tweets.
The sentiment analysis reveals that social media posts about the paper were largely negative. However, closer inspection reveals that this negativity is predominantly towards the findings of the paper, not the research itself.
For example, a Bluesky post on the “distressing” findings by one of the study’s authors is designated as “neutral negative” by Altmetric’s AI analysis.
In a response to a query from Carbon Brief, Altmetric explains that the “goal is to measure how people feel about the research paper itself, not the topic it discusses”. However, in some cases the line can be “blurred” as the AI “sometimes struggles to separate the subject matter from the critique”. The organisation adds that it is “continuously working on improving our models to better distinguish between the post’s content and the research output”.
On the attention that the paper received, lead author Dr Collin Edwards of Washington State University in Vancouver says that “first and foremost, people care about butterflies and our results are broad-reaching, unequivocal and, unfortunately, very concerning”.
Edwards tells Carbon Brief he hopes the clarity of the writing made the paper accessible to readers, noting that he and his co-authors “sweat[ed] over every word”.
The resulting news coverage “accurately captured the science”, Edwards says:
“Much as I wish our results were less consistently grim, the consistency and simplicity of our findings mean that even if a news story only provides the highest level summary, it isn’t misleading readers by skipping some key caveat or nuance that changes the interpretation.”
Warming ‘acceleration’
In third place in Carbon Brief’s list for 2025 is the latest scientific paper from veteran climatologist Dr James Hansen, former director of the NASA Goddard Institute for Space Studies and now adjunct professor at Columbia University’s Earth Institute.
The paper, titled “Global warming has accelerated: Are the UN and the public well-informed?” was published in the journal Environment: Science and Policy for Sustainable Development. It generated an Altmetric score of 3,474.
The study estimates that the record-high global temperatures in the last few years were caused by a combination of El Niño and a reduction in air pollution from international shipping.
The findings suggest that the cooling effect of aerosols – tiny, light‑scattering particles produced mainly by burning fossil fuels – has masked more of the warming driven by greenhouse gases than previously estimated by the IPCC.
As efforts to tackle air pollution continue to reduce aerosol emissions, warming will accelerate further – reaching 2C by 2045, according to the research.
The paper was covered by almost 400 news stories – driven, in part, by Hansen’s comments in a press briefing that the Paris Agreement’s 2C warming limit was already “dead”.
Hansen’s analysis received a sceptical response from some scientists. For example, Dr Valerie Masson-Delmotte, an IPCC co-chair for its most recent assessment report on climate science, told Agence France-Presse the research “is not published in a climate science journal and it formulates a certain number of hypotheses that are not consistent with all the available observations”.
In addition, other estimates, including by Carbon Brief, suggest new shipping regulations have made a smaller contribution to warming than estimated by Hansen.
Hansen tells Carbon Brief that the paper “did ok” in terms of media coverage, although notes “it’s on [scientists] to do a better job of making clear what the core issues are in the physics of climate change”.
With more than 1,000 tweets, the paper scored highest in the top 25 for posts on Twitter. It was also mentioned in more than 800 Bluesky posts and on 27 blogs.
The sentiment analysis suggests that these posts were largely positive, with just a small percentage of negative comments.
Making the top 10
Ranking fourth in Carbon Brief’s analysis is a Nature paper calculating changes in global glacier mass over 2000-23. The study finds glaciers worldwide lost 273bn tonnes of ice annually over that time – with losses increasing by 36% between 2000-11 and 2012-23.
The study has an Altmetric score of 3,199. It received more news coverage than any other paper in this year’s top 25, amassing 1,187 mentions. with outlets including the Guardian, Associated Press and Economic Times.
At number five, with an Altmetric score of 2,860, is the EAT-Lancet Commission on healthy, sustainable and just food systems.
Carbon Brief’s coverage of the report highlights that “a global shift towards ‘healthier’ diets could cut non-CO2 greenhouse gas emissions, such as methane, from agriculture by 15% by 2050”. It adds:
“The findings build on the widely cited 2019 report from the EAT-Lancet Commission – a group of leading experts in nutrition, climate, economics, health, social sciences and agriculture from around the world.”
Also making the top 10 – ranking sixth and eighth – are a pair of papers published in Nature, which both link extreme heat to the emissions of specific “carbon majors” – large producers of fossil fuels, such as ExxonMobil, Shell and Saudi Aramco,.
The first is a perspective, titled “Carbon majors and the scientific case for climate liability”, published in April. It begins:
“Will it ever be possible to sue anyone for damaging the climate? Twenty years after this question was first posed, we argue that the scientific case for climate liability is closed. Here we detail the scientific and legal implications of an ‘end-to-end’ attribution that links fossil fuel producers to specific damages from warming.”
The authors find “trillions (of US$) in economic losses attributable to the extreme heat caused by emissions from individual companies”.
The paper was mentioned 1,329 times on Bluesky – the highest in this year’s top 25. It was also mentioned in around 270 news stories.
Published four months later, the second paper uses extreme event attribution to assess the impact of climate change on more than 200 heatwaves recorded since the year 2000.
The authors find one-quarter of the heatwaves would have been “virtually impossible” without human-caused global warming. They add that the heatwaves were, on average, 1.7C hotter due to climate change, with half of this increase due to emissions stemming from the operations and production of carbon majors.
This study was mentioned in almost 300 news stories – including by Carbon Brief – as well as 222 tweets and 823 posts on Bluesky.
In seventh place is a Nature Medicine study, which quantifies how heat-related and cold-related deaths will change over the coming century as the climate warms.
A related research briefing explains the main findings of the paper:
“Heat-related deaths are estimated to increase more rapidly than cold-related deaths are estimated to decrease under future climate change scenarios across European cities. An unrealistic degree of adaptation to heat would be required to revert this trend, indicating the need for strong policies to reduce greenhouse gases emissions.”
The paper was mentioned 345 times in the news, including in the Financial Times, New Scientist, Guardian and Bloomberg.
The paper in ninth place also analyses the health impacts of extreme heat. The study, published in Science Advances, finds that extreme heat can speed up biological ageing in older people.
Rounding out the top 10 is a Nature Climate Change study, titled “Rising temperatures increase added sugar intake disproportionately in disadvantaged groups in the US”.
The study finds that at higher temperatures, people in the US consume more sugar – mainly due to “higher consumption of sugar-sweetened beverages and frozen desserts”. The authors project that warming of 5C would drive additional sugar consumption of around 3 grams per day, “with vulnerable groups at an even higher risk”.
Elsewhere in the top 25
The rest of the top 25 includes a wide range of research, from “glacier extinction” and wildfires to Amazon drought and penguin guano.
In 13th place is a Nature Climate Change study that finds the wealthiest 10% of people – defined as those who earn at least €42,980 (£36,605) per year – contributed seven times more to the rise in monthly heat extremes around the world than the global average.
The authors also explore country-level emissions, finding that the wealthiest 10% in the US produced the emissions that caused a doubling in heat extremes across “vulnerable regions” globally.
(See Carbon Brief’s coverage of the paper for more details.)
In 15th place is the annual Lancet Countdown on health and climate change – a lengthy report with more than 120 authors.
The study warns that “climate change is increasingly destabilising the planetary systems and environmental conditions on which human life depends”.
This annual analysis from the Lancet often features in Carbon Brief’s top 25 analysis. After three years in the Carbon Brief’s top 10 over 2020-23, the report landed in 20th place in 2023 and missed out on a spot in the top 25 altogether in 2024.
In 16th place is a Science Advances study, titled “Increasing rat numbers in cities are linked to climate warming, urbanisation and human population”. The study uses public complaint and inspection data from 16 cities around the world to estimate changes in rat populations.
It finds that “warming temperatures and more people living in cities may be expanding the seasonal activity periods and food availability for urban rats”.
The study received 320 new mentions, including in the Washington Post, New Scientist and National Geographic.
In 21st place is a Nature Climate Change paper, titled “Peak glacier extinction in the mid-21st century”. The study authors “project a sharp rise in the number of glaciers disappearing worldwide, peaking between 2041 and 2055 with up to ~4,000 glaciers vanishing annually”.
Completing the top 25 is a Nature study on the “prudent planetary limit for geological carbon storage” – where captured CO2 is injected deep underground, where it can stay trapped for thousands of years.
In a Carbon Brief guest post, study authors Dr Matthew Gidden and Prof Joeri Rogelj explain that carbon dioxide removal will only be effective at limiting global temperature rise if captured CO2 is injected “deep underground, where it can stay trapped for thousands of years”.
The guest post warns that “geological carbon storage is not limitless”. It states that “if all available safe carbon storage capacity were used for CO2 removal, this would contribute to only a 0.7C reduction in global warming”.
Top journals
The journal Nature dominates Carbon Brief’s top 25, with seven papers featured.
Many other journals in the Springer Nature stable also feature, including Nature Climate Change (three), Communications Earth & Environment (two), as well as Nature Ecology & Evolution, Nature Medicine and Nature Reviews Earth & Environment (one each).
Also appearing more than once in the top 25 are Science Advances (three), Science (two) and the Lancet (two).
This is shown in the graphic below.
All the final scores for 2025 can be found in this spreadsheet.
Diversity in the top 25
The top 25 climate papers of 2025 cover a huge range of topics and scope. However, analysis of their authors reveals a distinct lack of diversity.
In total, the top 25 includes more than 650 authors – the highest number since Carbon Brief began this analysis in 2022.
This is largely due to a few publications with an exceptionally high number of authors. For example, the 2025 report of the Lancet Countdown on health and climate change has almost 130 authors alone, accounting for almost one-fifth of authors in this analysis.
Carbon Brief recorded the gender and country of affiliation for each of these authors. (The methodology used was developed by Carbon Brief for analysis presented in a special 2021 series on climate justice.)
The analysis reveals that 88% of the authors of the climate papers most featured in the media in 2025 are from institutions in the global north.
Carbon Brief defines the global north as North America, Europe, Japan, Australia and New Zealand. It defines the global south as Asia (excluding Japan), Africa, Oceania (excluding Australia and New Zealand), Latin America and the Caribbean.
The analysis shows that 53% of authors are from European institutions, while only 1% of authors are from institutions in Africa.
Further data analysis shows that there are also inequalities within continents. The map below shows the percentage of authors from each country, where dark blue indicates a higher percentage. Countries that are not represented by any authors in the analysis are shown in grey.
The top-ranking countries on this map are the US and the UK, which account for 26% and 16% of the authors, respectively.
Carbon Brief also analysed the gender of the authors.
Only one-third of authors from the top 25 climate papers of 2025 are women and only five of the 25 papers list a woman as lead author.
The plot below shows the number of authors from each continent, separated into men (dark blue) and women (light blue).
The full spreadsheet showing the results of this data analysis can be found here. For more on the biases in climate publishing, see Carbon Brief’s article on the lack of diversity in climate-science research.
The post Analysis: The climate papers most featured in the media in 2025 appeared first on Carbon Brief.
Analysis: The climate papers most featured in the media in 2025
China and India have declined to back any of their old United Nations carbon credit projects seeking to sell offsets under the new UN market, driving a cull of nearly three-quarters of applicants, analysis of official data shows.
Only 415 out of more than 1,500 projects and programmes hoping to move from the Clean Development Mechanism (CDM) to the new carbon market set up under Article 6.4 of the Paris Agreement won the approval of their host governments by the 30 June deadline – a crucial step in transitioning them.
The two Asian giants, home to two-thirds of all applicants, account for the bulk of the exclusions. Brazil, the other heavyweight of the CDM era, took the opposite path, approving nearly all of its projects in a last-minute rush that leaves it with the largest number of activities still in the running to sell credits under the new mechanism.
Carbon market watchers have long regarded the CDM, set up under the Kyoto Protocol which has now been largely replaced by the Paris Agreement, as largely discredited for failing to drive real emission cuts. They also warned that letting its projects live on could dent confidence in the mechanism’s successor.
-
EU carbon credits could supercharge world’s clean cooking push, France says
The country’s top climate envoy says he discussed using cookstove carbon credits with TotalEnergies, which is working to expand the use of LPG cooking in Africa
If all projects seeking transition had been successful, they could have flooded the market with up to more than 900 million credits generated with largely outdated rules, according to UN estimates. One credit is equivalent to one tonne of carbon dioxide (CO2) and 900 million tonnes is similar to Japan’s annual emissions.
‘New era’
Injy Johnstone, senior research fellow at the Munich-based Max Planck Institute, said the failure of most projects to clear the hurdle sent a significant signal that carbon trading had entered a new era. “The system is trying to remove some of the hot air that had inflated it in the past,” she told Climate Home News.
“The lack of transition is the biggest contribution that Article 6 has made to climate yet,” she added, arguing that leaving “zombie credits” in the market creates confusion, especially for buyers that might not realise these units have lost their value.
Among the schemes that failed to win government approval are nine programmes promoted by fossil fuel companies over a decade ago to subsidise the construction of gas plants in the Global South, which Climate Home News has previously reported on.
Fossil fuel firms seek UN carbon market cash for old gas plants
But one of them, supporting the Ressano Garcia gas plant in Mozambique, could still profit from the new market after the country’s government granted its approval on deadline day itself.
Brazil leads projects transition
Established in 1997 under the Kyoto Protocol, the CDM allowed rich countries to meet part of their climate obligations by financing emission-cutting projects in poorer ones. It drew widespread criticism over its patchy human rights record and for failing to deliver promised climate benefits. Backers of the Article 6.4 market say it is a higher-integrity successor.
CDM projects were given a route back into the new mechanism under certain conditions at COP26 in Glasgow in November 2021, when governments agreed the rules for the Paris Agreement market.
Project developers had until the end of 2023 to apply and host governments were originally given until the end of 2025 to grant approval. But, after requests from many developing countries for an extension, at COP30 in Belém countries agreed to push the deadline back six months to the end of June.
Brazil was the single largest beneficiary of the decision, with all of its 92 approvals coming during the extension window. Hydropower plants, landfill gas schemes and wind farms make up the bulk of the South American country’s surviving portfolio, and hydro is the single most common project type in the global transition pipeline.
Peru greenlit the move of nearly a dozen hydropower plants, Thailand backed a batch of biogas and waste-to-energy schemes, and Mexico squeezed all of its approvals – including a controversial industrial gas project – into the final week. African nations including Zambia, Malawi and Ethiopia backed programmes aiming to switch households to cleaner cooking stoves, which have the potential to generate millions of offsets and are set to be the biggest source of credits among the surviving projects.
Long way from selling credits
Securing government support does not mean a scheme can now automatically sell credits under the Article 6 mechanism. Developers are required to submit additional documentation by the end of 2026 demonstrating that their programmes respect the mechanism’s stricter rules on environmental and social safeguards and on the risk of emission cuts being reversed. The Article 6.4 Supervisory Body, the mechanism’s regulator, has the final say on which projects are allowed into the market.
Those that make it through can sell credits for emission reductions achieved between 2021 and 2025 under the old CDM methodologies, with some adjustments aimed at preventing the creation of excess credits not backed by real emission cuts. For reductions achieved from 2026 onwards, projects will need to switch to new methodologies, which the regulator is currently developing.
So far, 30 programmes have completed the process, and only two cookstove projects in Myanmar have been formally approved to issue credits.
Civil society groups have called for an investigation into the activities in Myanmar over its ties to Myanmar’s military junta – which the UN says is guilty of human rights abuses – and allegations of “massively” overstating its climate impact.
The company behind the scheme said its engagement with authorities “should not be interpreted as political endorsement” of the junta, while disputing the calculations underpinning the claim that too many credits had been issued.
The post Most “zombie credits” locked out of new UN carbon market after China and India snub appeared first on Climate Home News.
Most “zombie credits” locked out of new UN carbon market after China and India snub
Climate Change
Debriefed 17 July 2026: UK ‘firewave’ | Fossil-fuelled heat deaths | London’s Natural History Museum spotlights climate
Welcome to Carbon Brief’s DeBriefed.
An essential guide to the week’s key developments relating to climate change.
This week
Heat and firewaves
‘FIREWAVE’: Wildfires ravaged Europe and North America this week. France utilised water-dumping planes collecting from the Seine to contain a fire in the Fontainebleau forest near Paris, according to the Associated Press. The Financial Times reported that the UK has had “25 non-consecutive days with temperatures of 30C or more, including nine days above 34C”, creating a “firewave” and putting pressure on emergency services. Meanwhile, an “orange haze from Canada wildfires” could be “seen in Ontario and northern US”, said BBC News.
‘NEW NORMAL’: Climate events previously seen as extreme are becoming the “new ‘normal’”, said the Met Office, in a report on the UK’s climate. While last year was the UK’s hottest on record, rising temperatures mean it is expected to be surpassed in the next few years, reported Reuters. Liz Bentley, head of the Royal Meteorological Society, told the Guardian that “climate change has been described by scientists for many years but is now increasingly being felt by the UK population in their own homes and communities”.
Around the world
- ELECTRIFYING PUSH: The European Commission has announced a target for electricity to account for 46% of energy consumption across the bloc by 2040, reported Carbon Pulse. The commission has also made plans to adapt its emissions trading system to “bring relief to industry”, it said.
- FALLING OIL: The International Energy Agency said that global oil demand is expected to decline this year for the first time since 2020, reported the Associated Press.
- US ROLLBACKS: Trump cuts to clean energy support “led to the cancellation or delay of $83bn in investment across hundreds of projects”, reported Reuters. The Trump administration has also changed environmental law to allow development in the habitats of endangered species, according to CNN.
- BURNHAM BEGINS: Incoming UK prime minister Andy Burnham is preparing to announce new North Sea drilling “within days of taking office”, said Bloomberg. Carbon Brief looked at 28 statements that Burnham has made about climate change and fossil fuels.
- DRY JULY: Drought in Uganda led to significant crop losses and at least 16 deaths from starvation, said BBC News.
- ON AI: Australia planned to implement restrictions on energy and water usage for datacentres “amid [an] AI boom”, said the New York Times.
38%
The drop in Brazilian Amazon deforestation in the first half of 2026, compared to last year, reported Al Jazeera.
Latest climate research
- The area of land burned by wildfires in Africa each year has reduced due to a shrinking dry season | Geophysical Research Letters
- Most people do not distinguish between climate adaptation and mitigation when thinking about tackling climate change | Climate Outreach
- An “effort-sharing framework” has been developed to support progress towards the Paris Agreement | npj Climate Action
(For more, see Carbon Brief’s in-depth daily summaries of the top climate news stories on Monday, Tuesday, Wednesday, Thursday and Friday.)
Captured
Carbon Brief explained how more than 1,000 heat-related deaths in England and Wales during May and June were attributed to climate change, accounting for almost half of all heat-related deaths experienced during those months. The article also unpacked the different methods for estimating heat deaths around the world.
Spotlight
Natural History Museum exhibits climate change
This week, Carbon Brief interviews Meaghan Macdonald, senior project and programme manager for London’s Natural History Museum, about their first permanent climate-themed exhibition, Fixing Our Broken Planet.
Carbon Brief: Why are programmes such as Fixing Our Broken Planet so important?
Meaghan Macdonald: One of the main things we’re trying to achieve with Fixing Our Broken Planet is to place the museum as a convener of conversations around the planetary emergency…trying to bring together the different groups of people who need to be involved in this conversation in order to work together to find a solution.
And we find that a lot of the people who come into the gallery weren’t necessarily coming here to see it; they come across it, which is a really great way to engage people who may not have been engaged in that discussion previously.
CB: How does the exhibition engage and inspire visitors?
MM: A driving force for this exhibition is that you are dealing with a subject matter that can be quite disheartening, and one of the things that we were very careful about is to try to make sure that woven throughout the scientific data… is a sense of hope… to enable people to feel empowered to make a difference.
We were able to do things like our “what you can do” labels, which give an example that people can take away with them. We also have “conversation starters”, which is a digital screen that asks people a series of questions related to the planetary emergency. Things like: “Should we mine the deep sea to power the green economy?”…And there’s no right or wrong answer.
We [also] set out very specifically to…forefront the science that’s happening here. We know from multiple studies from thinktanks and organisations that people actually trust our scientists the most.
CB: The museum has set out a goal to “create advocates for the planet”. What does this mean? How does it relate to the exhibition and the museum’s wider climate action?
MM: The aim of the museum is to get to a place where both people and the planet thrive. Being a library of the natural world, it is our duty to be standing up for it and to help people find their way, fighting for nature’s side.
In order to create those advocates, the aim of the [exhibition] and the wider advocacy programmes at the museum is to try to find ways to bring all these people [individuals, policymakers, industry, scientists] together.
We have the wider programme with Fixing Our Broken Planet. We have Generation Hope…a free graphic panel version of our display in the gallery that we have been able to get into a number of venues in Bangalore…the very long-standing and beloved wildlife photographer of the year [exhibition]…our urban nature movement…[and] an initiative that we are doing with the Department for Education called the National Education Nature Park.
Watch, read, listen
STUBBORN HOPE: For the Conversation, climate scientist Prof Peter Stott argued that researchers need to “talk more about the very worst-case scenarios” and the possibility for action.
EXTREME: Vox’s the Gray Area podcast spoke to New York Times journalist David Wallace-Wells about the possibility of a “Godzilla” El Niño.
RESPONSIBILITY: For Climate Home News, two researchers from the Center for International Environmental Law explored how “major emitting countries knew of climate risks decades earlier than claimed”.
Coming up
- 13-31 July: Meeting of the International Seabed Authority assembly and council, Kingston, Jamaica
- 17-19 July: 3rd International Conference on Environment and Sustainable Development, London
- 19 July: Presidential election, São Tomé and Príncipe
Pick of the jobs
- Zero Carbon Analytics, research lead | Salary: Unknown. Location: Remote
- Met Office, ocean climate scientific manager | Salary: £54,515-£58,582. Location: Exeter
- National Trust, land use and nature delivery partner | Salary: £44,499. Location: Newcastle or York
DeBriefed is edited by Daisy Dunne. Please send any tips or feedback to debriefed@carbonbrief.org.
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The post Debriefed 17 July 2026: UK ‘firewave’ | Fossil-fuelled heat deaths | London’s Natural History Museum spotlights climate appeared first on Carbon Brief.
Recent weeks have seen a flurry of reports from public health authorities and scientists that estimate the deaths caused by Europe’s record-breaking summer heatwaves.
In France, the national public health agency reported 2,025 excess deaths over the week where the heatwave peaked in June.
Authorities in Germany and Netherlands put the excess death toll during the same seven-day period at 5,753 and 533, respectively.
An analysis from climate scientists in Carbon Brief found that France saw more than 2,700 heat-related deaths over 17 days in June.
Separate research estimated there had been 2,700 heat-related deaths in the UK’s May and June heatwaves – 42% of which had been caused by human-caused climate change.
There are a number of methods for how academics and governments tally deaths caused by extreme heat, each with their own advantages and drawbacks.
Here, Carbon Brief looks at the different ways scientists and public health authorities have calculated the death toll of Europe’s record-breaking summer heat.
- How established is the science of calculating heat deaths?
- What are the different approaches to counting heat deaths?
- What do the latest figures show for Europe’s May and June heatwaves?
- What are the pros and cons of the ‘excess deaths’ method?
- What are the pros and cons of the ‘statistical modelling’ method?
How established is the science of calculating heat deaths?
Economists and epidemiologists have been studying the relationship between heat and mortality for nearly a century.
A pioneering study published in 1923 by geographer Ellsworth Huntington and economist Margaret Justin that looked at mortality data for New York City over 1882-88 found that deaths increased rapidly as temperatures rose above 17C.
As global temperatures have risen in response to human-caused carbon emissions, scientists have increasingly sought to understand how warming could impact mortality.
The study of mortality caused by specific heatwave events dates back a few decades, with a 1995 heatwave in Chicago among the earliest events to be studied in detail.
Over the past decade, a growing number of studies have gone a step further, by estimating the number of deaths caused by a specific heatwave event and then attributing a percentage or number of those deaths to human-caused climate change.
Carbon Brief covered the first study of this type, which was published in Environmental Research Letters in 2016 and focused on a 2003 summer heatwave that caused tens of thousands of deaths across Europe.
The study estimated that 506 of the 735 summer fatalities in Paris and 64 of the 315 in London were a result of human influence on the climate.
More recently, a study in Climatic Change found that 27% of deaths in a 2018 heatwave in Zurich, Switzerland were linked to human-caused climate change and a paper in Science Advances estimated that 11-15% of deaths in a 2021 heatwave in British Columbia were attributable to global warming.
Dr Christopher Callahan, assistant professor at the O’Neill School of Public and Environmental Affairs at Indiana University, tells Carbon Brief this type of “two-step” study has “really exploded” in recent years:
“It is really only in the last five to 10 years that we have seen this, partly because it does require interdisciplinary expertise. You need people who know how to run the epidemiological models and you need a climate analysis of the counterfactual [world] without climate change, which is its own effort.”
What are the different approaches to counting heat deaths?
A central challenge in estimating deaths from a heatwave is that heat is rarely recorded as the primary cause of death on death certificates.
However, exposure to high temperatures has wide-ranging effects on the human body, including the strain of keeping cool. This effort places pressure on the heart and kidneys.
As a result, heat extremes can worsen health risks from chronic conditions and cause acute kidney injury. Researchers have linked heat to increased mortality from respiratory and cardiovascular diseases, as well as dementia and Alzheimer’s.
As a result, public health authorities and scientists cannot depend on death certificates for a full count of heat-related deaths. They instead estimate heat deaths using a number of different approaches, each with assumptions baked into their calculations.
Dr Garyfallos Konstantinoudis, who researches methods for calculating excess mortality due to extreme events at the Grantham Institute for Climate Change and the Environment at Imperial College, tells Carbon Brief there is “no ground truth” when it comes to tallying heat-related deaths:
“We don’t know what the heat-related deaths are, so we rely on different models to describe the picture.”
This makes the study of deaths from heatwaves similar to those from air pollution, he says:
“This sort of health-impact assessment has been done for years on studies related to deaths from air pollution, which have the same problem. Air pollution, until very recently, was not recorded on death certificates.
“[However], for air pollution, the [scientific] literature is much larger, so no one questions that air pollution is toxic and kills. This sort of messaging for heat is more recent.”
There are, broadly speaking, two approaches to calculating deaths during a heatwave.
The first involves counting the number of excess deaths relative to a period in the past.
This method – often referred to as an “excess deaths” approach – looks at how many people died during a particular time period compared to a baseline period where there was no heatwave.
To do this, public health authorities and researchers rely on official death figures reported by country authorities.
The heat death tolls published in recent weeks by public health agencies in Belgium, France, Germany and the Netherlands relied on this approach.
(For more, see: What are the pros and cons of the ‘excess deaths’ method?)
The second method uses long-term mortality data to understand the statistical relationship between temperature and mortality in a given place. The model that emerges can be used to infer the number of deaths from a heatwave in that place.
In a rapid analysis published this week, researchers at Imperial College London, the London School of Hygiene and Tropical Medicine (LSHTM) and the Met Office used this approach to estimate that the May and June heatwaves in the UK caused the deaths of 2,700 people.
Dr Callahan – working with Prof Andrew Dessler, director of the Texas Center for Extreme Weather at Texas A&M University – used this method to estimate that more than 2,700 people had died in France over a 17-day period in June in an analysis for Carbon Brief.
(For more: see: What are the pros and cons of the ‘statistical modelling’ method?)
The majority of the figures released in the wake of Europe’s June heatwave have relied on these two methods.
There is a third way to calculate heat deaths, which is to look at official counts of deaths attributed on death certificates to heatstroke.
Callahan tells Carbon Brief that the “death-certificate coding” appears to have fallen out of favour in Europe – which he says is a “smart move” given that it does not provide a “full accounting”.
Nevertheless, some public health authorities are still using this method. For example, in the wake of the heatwave in the US earlier this month, public health data showed 29 people in New Jersey and three people in New York had died from “heat-related illnesses”.
Scientists tell Carbon Brief the excess deaths and statistical modelling approaches both have advantages and drawbacks. These are explored below.
What do the latest figures show for Europe’s May and June heatwaves?
The table below shows the death numbers that have been reported by governments and researchers for Europe’s May and June heatwaves, including the approach used to reach the figures.
It suggests that multiple countries in Europe experienced more than 1,000 heat-related deaths during the late June heatwave, with authorities in Germany counting more than 5,000.
Meanwhile, the EuroMoMo mortality monitoring system estimated there were more than 10,500 excess deaths across 27 countries during the June heatwave.
| Reported | Source | Country / region | Dates | Days | Deaths | Link | Approach |
|---|---|---|---|---|---|---|---|
| 28/06/2026 | Public Health France | France | 22-27 June | 6 | 1,000 | santepubliquefrance.fr | Excess deaths |
| 29/06/2026 | World Health Organization | Europe | 21-28 June | 8 | 1,300 | x.com/DrTedros/status | Excess deaths |
| 01/07/2026 | Carlos III Health Institute (MoMo) | Spain | 1-30 June | 30 | 1,033 | dw.com | Excess deaths (all-cause and temperature-attributable) |
| 02/07/2026 | National Institute for Public Health and the Environment | Netherlands | 22-28 June | 7 | 480 | rivm.nl | Excess deaths |
| 03/07/2026 | Public Health France | France | 22-28 June | 7 | 2,025 | santepubliquefrance.fr | Excess deaths |
| 07/07/2026 | Chris Callahan/Andrew Dessler | France | 12-29 June | 18 | 2,766 | carbonbrief.org | Statistical modelling |
| 08/07/2026 | Chris Callahan | Europe | 15-28 June | 14 | 13,975 | zenodo.org | Statistical modelling |
| 08/07/2026 | Sciensano | Belgium | 18 June – 1 July | 14 | 1,747 | brusselstimes.com | Excess deaths |
| 09/07/2026 | Robert Koch Institute | Germany | 22-28 June | 7 | 5,120 | rki.de | Statistical modelling |
| 13/07/2026 | Met Office/LSHTM/Imperial | England and Wales | 22-27 June | 6 | 2,183 | drive.google.com | Statistical modelling |
| 13/07/2026 | Met Office/LSHTM/Imperial | England and Wales | 24-26 May | 3 | 553 | drive.google.com | Statistical modelling |
| 13/07/2026 | EURO Mo/Mo | 27 European countries | 22-28 June | 7 | 10,650 | reuters.com | Excess deaths |
| 07/07/2025 | National Institute for Public Health and the Environment | Netherlands | 22-28 June | 7 | 577 | archive.ph | Excess deaths |
| 14/07/2026 | Germany Federal Statistical Office (Destatis) | Germany | 22-28 June | 7 | 5,753 | destatis.de | Excess deaths |
In most instances, Carbon Brief has linked to the figures published by public health authorities, where numbers were first reported. In some instances, figures were released on dashboards or webpages that are updated weekly. In these cases, Carbon Brief has linked to media reports or archived web content.
What are the pros and cons of the ‘excess deaths’ method?
The excess deaths approach looks at how many more people died during a particular time period compared to a baseline period of the same length.
For instance, on 14 July, Germany’s federal statistics agency, Destatis, published figures showing Germany saw 32% more deaths than the average in the week of 22-28 June, which was dominated by the heatwave.
Specifically, the agency said that 23,932 deaths had been recorded that week, compared to an average of 18,179 in that calendar week across the years 2022-25.
This suggests there were 5,753 excess deaths during the heatwave week. (This was a slight increase from preliminary Destatis figures released a week earlier, covered by Bloomberg.)
The Netherlands similarly calculates excess deaths by comparing death figures against an average of deaths in a similar period during unspecified “previous years”.
Data published by the country’s National Institute for Public Health and the Environment (RIVM) shows that, during the week of 22-28 June, an estimated 3,626 people died in total in the northern European country.
This is 577 more deaths than the 3,049 expected at that time of year, it said. (This is a slight revision upwards from the 480 excess deaths reported on 4 July by NL Times based on preliminary figures from NVIM.)
Callahan says that the excess deaths approach has the benefit of being rapid and relatively uncomplicated:
“It is something that public health authorities can put out fairly quickly without having to run a fancy model and do coding like the academic scientists do. It is a short-term, high-impact, rapid estimate of mortality.”
The drawback to the approach is that it is impossible to decipher what percentage of these “all-mortality” excess deaths are, in fact, heat-related.
Imperial College’s Konstantinoudis notes that the public often “feels more comfortable” with the excess deaths approach over the statistical modelling approach because the data it is using – the official death numbers – is based on real-world data.
However, he stresses that excess deaths figures are based on a series of assumptions, including the reference period picked by researchers and how the numbers are interpreted.
Statisticians and researchers have to make a series of decisions, including what period to use as a comparative baseline. For example, the baseline period could be the week before a heatwave, the same week a year before – or an average of the same week across multiple years in the past. If averaging mortality of a similar period across a number of previous years, they must decide how much “weight”, or influence, each year should have.
They must also decide how to account for spikes in deaths during the Covid-19 pandemic years, as well as the gradual rise in average temperatures due to global warming.
During the pandemic, many governments and the World Health Organization (WHO) used the excess deaths approach to count deaths. The WHO said this metric was more “comparable” and “objective” than relying on national reports of Covid-19 deaths, given that different countries used different criteria for this classification.
A notable example of how assumptions can skew excess death figures came during this period, when the WHO estimated in 2022 that Germany had seen 195,000 excess deaths over two years of pandemic.
However, after statisticians and epidemiologists pointed out the assumptions in the model were not suited to Germany’s demographics, the WHO retracted the figure and eventually reduced it to 122,000 and then later to 102,000.
Konstantinoudis explains:
“Covid taught us that it is complicated. Depending on the different assumptions used in the excess-mortality approach, you get different results…There is a scientific basis, but we should acknowledge the assumptions.”
What are the pros and cons of the ‘statistical modelling’ method?
In the statistical modelling approach, researchers use models to determine the specific relationship between mortality and temperature for a particular location and then apply it to temperatures observed during a heatwave.
This allows them to estimate the overall number of deaths that were caused by a heatwave.
Previous research has revealed that, in most places of the world, there is a U-shaped response of mortality to temperature – where deaths increase rapidly in cold or hot conditions as daily maximum temperatures depart further from an “optimum temperature”.
For example, research published in Proceedings of the National Academy of Sciences in 2025 found that mortality rates in France rise as daily maximum temperatures move away from approximately 20C. This is shown in the chart below.
Indiana University’s Callahan say this approach allows scientists to “formally establish a relationship between the temperature and the mortality”, adding:
“If you do these calculations right, you can credibly say your entire estimate of mortality is heat-related.”
Prof Antonio Gasparrini, biostatistician and epidemiologist at LSHTM, explains the method relies on “timeseries models that apply relatively sophisticated statistical methods in which you ‘smooth’ trends occurring in time, so you control for long-term trends and seasonality”.
He says that these models also allow researchers to “remove” trends affecting mortality that are unrelated to heat – for instance, the impacts of the pandemic. They can also “add” other information, such as around how air pollution combines with heat to threaten vulnerable populations.
Gasparrini adds:
“What statistical modelling can bring is that it is more refined. It can link specific temperatures to specific impacts rather than just looking at the event [in the whole]. And also, it can be localised – [data] can be stratified at a fine scale and we can look at impacts at different scales.
“So, it is more informative. But, at the same time, of course, it’s based on more assumptions than the [excess deaths approach] and, of course, needs to be checked and compared.”
The approach depends on a number of judgment calls from scientists and statisticians, including the years picked to underpin the model and how to capture the lag in deaths in the days and weeks after a heatwave event.
They must also decide at what threshold to start counting deaths – in other words, whether to count all deaths above the “optimum temperature” or set a higher, more extreme value – and whether and how to account for any adaptation to heat extremes that may have been put in place in the study area.
A benefit of the statistical modelling approach is that it opens the door for being able to attribute a specific number of deaths to human-caused climate change.
By applying the temperature-mortality curve to both the temperatures of the recent heatwave and a counterfactual world without climate change, scientists can estimate what proportion of estimated deaths only occurred because the world is warming.
For instance, Imperial College, LSHTM and Met Office researchers found that 59% and 38% of heat-related deaths in the UK’s May and June heatwaves, respectively, could be attributed to climate change. Their findings are shown in the chart below.
Some climate-sceptic commentators have argued that modelled estimates are hypotheses and should therefore be treated with caution.
On 13 July, climate-sceptic news website GB News covered a blog post by Oxford academics that argued the figure that 2,700 people had died in the UK’s May and June heatwaves was not reflected in the provisional “all-mortality” data put out by the UK’s Office for National Statistics (ONS). Quoting the blog, GB News said:
“Modelling tells us nothing. Models explore possibilities; surveillance tells us what happened. When the two disagree, our instinct should be to investigate the data rather than simply trust the model.”
However, Imperial’s Konstantinoudis – who worked on the models behind the 2,700 figure – says it is important to await the UK Health and Security Agency (UKHSA)’s annual heat mortality report before arriving at any conclusions. He explains:
“While we are entirely clear that our current findings are modelled estimates, this methodology has consistently delivered comparable results to the UKHSA’s own official analyses of observed deaths for past heat events.”
(The UKHSA report will include updated figures and estimate excess deaths from heat based on specific periods of heat in different regions, whereas the provisional ONS figures cover all national deaths during a full-week period.)
Konstantinoudis says both the excess deaths and statistical modelling approaches have been the subject of extensive peer-reviewed scientific study and can provide a “holistic view of what is happening” when used together.
Studies that have compared statistical modelling approaches for estimating heatwave deaths with excess death figures in the UK have found they yield broadly similar results.
The post Q&A: Europe’s May and June heatwave deaths – and how they were counted appeared first on Carbon Brief.
Q&A: Europe’s May and June heatwave deaths – and how they were counted
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