Hundreds of scientists in dozens of institutions are embarking on the next phase of the world’s largest coordinated climate-modelling effort.
Climate-modelling groups use supercomputers to run climate models that simulate the physics, chemistry and biology of the Earth’s atmosphere, land and oceans.
These models play a crucial role in helping scientists understand how the climate is responding as greenhouse gases build up in the atmosphere.
For four decades, the Coupled Model Intercomparison Project (CMIP) has guided the work of the climate-modelling community by providing a framework that allows for millions of results to be collected together and compared.
The resulting projections are used extensively in climate science and policy and underpin the landmark reports of the Intergovernmental Panel on Climate Change (IPCC).
Now, the seventh phase of CMIP – CMIP7 – is underway, with more than 30 climate-modelling centres expected to contribute more than five million gigabytes of data – so much that downloading it using a fast internet connection would take two and a half years.
Here, we look at what is new for CMIP7, including its model experiments, updated emissions scenarios and “assessment fast track” process.
What is CMIP?
Around the world, climate models are developed by different institutions and groups, known as modelling centres.
Each model is built differently and, therefore, produces slightly different results.
To better understand these differences, CMIP coordinates a common set of climate-model experiments.
These are simulations that use the same inputs and conditions, allowing scientists to compare the results and see where models agree or differ.
The figure below shows the countries that have either produced or published CMIP simulations.
During this time, scientists use new and improved models to run experiments from previous CMIP phases for consistency, as well as new experiments to investigate fresh scientific questions.
These simulations produce a trove of data, in the form of variables – such as temperature, rainfall, winds, sea ice extent and ocean currents. This information helps scientists study past, present and future climate change.
As scientific understanding and technical capabilities improve, models are refined. As a result, each CMIP phase incorporates higher spatial resolutions, larger ensembles, improved representations of key processes and more efficient model designs.
CMIP7 objectives
Each CMIP phase has an “experimental design” that outlines which climate-model experiments should be run and their technical specifications, including the time period the models should simulate.
The CMIP7 experimental design has several components.
As in CMIP6, for a modelling centre to contribute, they are asked to produce a suite of experiments that maintain continuity across past and future CMIP phases.
This suite of experiments is known as the “diagnostic, evaluation and characterisation of klima” (DECK) and is used to understand how their model “behaves” under simple, standard conditions. These experiments are designed and requested directly by CMIP’s scientific governing panel.
Alongside the DECK, CMIP also incorporates experiments developed by model intercomparison projects (MIPs) run by different research communities. For example, experiments exploring what the climate could look like under different levels of emissions or those that explore how sea ice might have changed between the last two ice-ages.
Currently, CMIP is working with 40 MIPs. These groups investigate specific scientific questions at their own pace, rather than on timelines prescribed by CMIP.
Running a large number of simulations can take modelling centres a long time. To speed up the process, CMIP7 has launched the “assessment fast track”.
This is a small subset of CMIP7 experiments, drawn from past and present community MIPs, identified through community consultation as being critical for scientific and policy assessments.
Data from the assessment fast track will be used in the reports that will together form the seventh assessment (AR7) of the IPCC.
It will also be used as an input by other groups that create climate information, including organisations involved in regional downscaling and modelling climate impacts and ice-sheet changes.
The figure below shows the different components of CMIP7. It shows how a subset of CMIP7 experiments will be delivered on an accelerated timeline, while the majority of experiments will be led by MIPs.
CMIP7 experiments
There are three categories of experiments set to take place in CMIP7:
- Historical experiments, which are designed to improve scientific understanding of past climates. Model runs exploring the recent historical period also allow scientists to evaluate the performance of models by checking how well they replicate real-world observations.
- Prediction and projection experiments, which allow scientists to analyse what different climates could look like under varying levels of greenhouse gas emissions, as well as near-term (10-year) prediction experiments.
- Process understanding experiments, which are designed to better understand specific processes and isolate cause-and-effect relationships. For example, a set of experiments might change the emissions of one greenhouse gas at a time to see how much each pollutant contributes to warming or cooling the climate.
Modelling centres typically produce and publish their data for the historical and projection experiments first.
CMIP expects the first datasets to be available by this summer, with broader publication recommended by the end of the year, in time to be assessed by IPCC AR7 authors.
Drafting of the reports of AR7 is currently underway. However, countries are yet to agree on the timeline for when they will be published. This presents a challenge for the climate-modelling community, given the difficulties of working with a moving deadline.
(For more on the ongoing standoff between countries around the timing of publication of the reports, read Carbon Brief’s explainer.)
New emissions scenarios
Scientists use emissions scenarios to simulate the future climate according to how global energy systems and land use might change over the next century.
Crucially, these scenarios – also known as “pathways” – are not forecasts or predictions of the future.
The group tasked with designing the scenarios for CMIP phases, as well as producing the “input files” for climate models, is the “scenario model intercomparison project”, or ScenarioMIP.
In a new paper, the group has set out the new set of scenarios for CMIP7:
- High (H): Emissions grow to as high as deemed plausibly possible, consistent with a rollback of current climate policies. This scenario will result in strong warming.
- High-to-low (HL): Emissions rise as in the high scenario at first, but are cut sharply in the second half of the century to reach net-zero by 2100.
- Medium (M): Emissions consistent with current policies, frozen as of 2025, leading to a moderate level of warming.
- Medium-to-low (ML): Emissions are slowly reduced, eventually reaching net-zero emissions by the end of the century.
- Low (L): Emissions consistent with likely keeping warming below 2C and not returning to 1.5C before the end of the century.
- Very low (VL): Emissions are cut to keep temperatures “as low as plausible”, according to the paper. This scenario limits warming to close to 1.5C by the end of the century, with limited overshoot beforehand.
- Low-to-negative (LN): Emissions fall slightly slower than in the VL scenario, with temperatures just rising above 1.5C. Emissions then rapidly drop to negative to bring warming back down.
The figures below show the emissions (left) and the estimated global temperature changes (right) under the seven new scenarios for CMIP7, from the low-to-negative emissions scenario (turquoise) to a high-emissions scenario (brown).
As a set, the ScenarioMIP scenarios “cover plausible outcomes ranging from a high level of climate change (in the case of policy failure) to low levels of climate change resulting from stringent policies”, the paper says.
Compared to the scenarios in CMIP6, the range in future emissions they cover is now narrower, the authors say:
“On the high-end of the range, the CMIP6 high emission levels (quantified by SSP5-8.5) have become implausible, based on trends in the costs of renewables, the emergence of climate policy and recent emission trends…At the low end, many CMIP6 emission trajectories have become inconsistent with observed trends during the 2020-30 period.”
Put simply, progress on climate policies and cheaper renewable technologies means that scenarios of very high emissions have now been ruled out.
However, this progress has not been sufficient to keep society on track for the Paris Agreement’s 1.5C goal. The paper notes that, “at this point of time, some overshoot of the 1.5C seems unavoidable”.
The change to the high end of the scenarios has sparked misleading commentary in the media and on social media – even from US president Donald Trump. A Carbon Brief factcheck unpacks the debate.
Also notable in the new scenarios is the “low-to-negative” pathway, which has the explicit feature of emissions becoming “net-negative”. In other words, through carbon dioxide removal (CDR) techniques, society reaches the point at which more carbon is being taken out of the atmosphere than is being added through greenhouse gas emissions.
Reaching net-negative emissions is fundamental to “overshoot scenarios”, where global warming passes a target and then is brought back down by large-scale CDR.
Overshoot scenarios allow scientists and policymakers to investigate the impacts of a delay to emissions reductions and better understand how the world might respond to passing a warming target. This includes the question of whether some impacts of climate change, such as ice sheet melt, are reversible.
CMIP has encouraged modelling centres to run simulations using the “high” and “very low” scenarios first to ensure downstream users of the data – including groups working on regional climate projections (CORDEX), climate impacts modelling (ISIMIP) and ice-sheet modelling (ISMIP) – have enough time to produce their data for IPCC reports.
These two scenarios were selected as they sit at opposite ends of the spectrum of climate outcomes. The high scenario will demonstrate how models behave under high emissions, while the very low scenario will demonstrate how models behave when emissions are rapidly reduced.
CMIP has recommended that modelling centres then run the “medium” and “high-to-low” scenarios. The remaining scenarios should then follow and no official recommendation has been made yet on their production order.
Other new features
In addition to the assessment fast track and new scenarios, CMIP7 has a number of other new developments.
Updated data for simulations
Climate models use input datasets to define the set of external drivers – or “forcings” – that have caused the global warming observed so far. These drivers include greenhouse gases, changes to incoming solar radiation and volcanic eruptions.
CMIP recommends modelling groups use the same input datasets, as this makes it easier to compare model results.
In CMIP7, the historical forcing datasets available for modelling groups to use have been improved to better represent real-world changes and extended closer to the present day. The historical simulations will be able to simulate the past climate from 1850 through to the end of 2021, whereas CMIP6 only simulated the past climate through to 2014.
CMIP is also planning to extend these historical datasets through to 2025 and maybe further throughout the course of CMIP7.
Emissions-driven simulations
CMIP7 introduces a new focus on CO2 emissions-driven simulations, providing a more realistic representation of how the climate responds to changes in emissions.
In older generations of climate models, atmospheric levels of CO2 and other greenhouse gas concentrations have been needed as an input to the model. These levels would be produced by running scenarios of CO2 emissions through separate carbon cycle models. The resulting climate-model runs were known as “concentration-driven simulations”.
However, many of the latest generation of models are now able to run in “emissions-driven mode”. This means that they receive CO2 emissions as an input and the model itself simulates the carbon cycle and the resulting levels of CO2 in the atmosphere.
This development is important, as climate policies are typically defined in terms of emissions, rather than overall atmospheric concentrations.
This new development in modelling will enable a more realistic representation of the carbon cycle and a better understanding of how it might change under different levels of warming.
Enhanced model documentation and evaluation
All CMIP7 models will be required to supply standardised model documentation that ensures consistency across model descriptions and makes it easier for end users to understand the data.
Additionally, CMIP scientists have developed a new open-access tool that dramatically speeds up the evaluation of climate models.
This “rapid evaluation framework” allows researchers to compare model outputs with real-world observations, providing immediate insight into model performance.
The post Guest post: How CMIP7 will shape the next wave of climate science appeared first on Carbon Brief.
Guest post: How CMIP7 will shape the next wave of climate science
The African continent’s hopes for a legally binding agreement to combat drought have been dashed again, as UN land restoration talks in Mongolia passed the issue onto the next set of talks in Egypt in two years’ time.
For over a decade, Africa has pushed for a UN protocol on drought risk management that would acknowledge drought as an issue requiring a regional and global – not just a national – response, potentially paving the way for more finance to help ensure water is available when drought hits.
A formal protocol would enable countries to transition from reacting to drought once it hits to “a proactive enabling mechanism to address drought and its effects such as migration”, said a Tunisian negotiator on behalf of the African Group of countries last week. Once land is regularly too dry and infertile to grow crops or graze animals, people often leave to seek a living elsewhere.
But this effort to adopt a protocol, led by Africa, has been resisted at successive land restoration COPs under the UN Convention to Combat Desertification (UNCCD), mainly by developed countries, which argue that a legally weaker alternative – a framework – would be faster and cheaper to set up.
Governments at the previous COP in Saudi Arabia in 2024 failed to reach agreement despite talks running past midnight, while this year’s saw African officials coordinate a walkout from negotiating rooms on Wednesday morning, according to two sources at the talks.
Drought deal delayed until 2028
The IISD’s Earth Negotiations Bulletin, a non-governmental organisation which unlike the media is allowed to watch and report on closed-door talks, said a call to suspend negotiations on Wednesday showed negotiations had reached “boiling point” and “made some jaws drop”.
Negotiations resumed after a lunchtime meeting with the Mongolian COP presidency although governments were only eventually able to agree that they could not find consensus in Ulaanbaatar and should resume talks on an instrument to deal with drought in 2028.
Christine Colvin, WWF’s head of freshwater policy, told Climate Home News that, with droughts hitting from Honduras to the English region of Hampshire, something concrete – whether a protocol or a framework – is needed urgently “rather than the can being kicked down the road for another two years as will now happen with the protocol procrastination”.
But, in a closing press conference on Friday, the Mongolian minister presiding over talks celebrated that governments had reached consensus on several “contentious” issues and that agenda items blocked at this year’s COP17 would be put on the agenda for COP18 in Egypt.
US blocks agenda items
Other agenda items that divided countries were on measuring land degradation’s effects on women, enhancing the involvement of civil society and women in land COPs, and the UNCCD working more closely and effectively with the UN’s climate and nature conventions.
On the COP’s opening day two weeks ago, the US representative said the Trump government objects to these agenda items “on their premise and no amount of negotiation will allow us to join consensus on these items. As such we request that they be struck from the agenda at which time we will then be able to approve it, saving us valuable negotiating time.”
A US State Department spokesperson later told Climate Home News that the US wants the UN “to get back to basics by refocusing on its core mandate, eliminating overlap, and reducing competition for scarce resources”.
The spokesperson added, “that means prioritising the concrete work member states created [the UN] to do – rather than diverting limited time, attention, and resources toward social and political agendas, including gender-related initiatives.”
On COP’s first day, the European Union and Brazil pushed back against the blocking of these agenda items, with a Brazilian negotiator saying his country attaches “great importance” to them. But the Mongolian presidency directed governments to adopt the rest of the agenda without the controversial items, which were discussed privately with countries throughout the two weeks.
An EU statement, read out later by Irish minister Timmy Dooley, accused “some parties” (meaning national governments) of having adopted a “less constructive approach” and preventing “discussions on important matters from even commencing”.
The agenda items the US refused to engage with were never discussed and were only placed onto the agenda for the next COP on the last day. Those talks will take place in Egypt in two years’ time, with Donald Trump due then to be in his last year as US president.
No restoration without women
The blocking of the gender agenda item has stymied attempts, agreed on by governments at the last COP, to develop gender-specific indicators for the UNCCD’s next overall framework and to facilitate more women delegates at COPs. Women made up only about a quarter of delegates to COP15 in 2022, UNCCD analysis with the latest data shows
Criticising the move to keep gender off the agenda, the EU said in a statement that it welcomes “the attention being given at COP17 to women pastoralists and herders, recognising their contribution to sustainable land management and resilient rural livelihoods”.
The head of the UNCCD, former Egyptian environment minister Yasmine Fouad, said on Friday that “regardless that the agenda item was blocked”, she was proud that she and COP17 President Batmunkh Battsetseg had led the COP as women and attended the gender caucus (a meeting of groups supporting women at the talks).
“Without the women,” she told the closing press conference on Friday, “we will not be able to restore land, restore hope, restore life or restore even our children and grandchildren. And we will keep on pushing that agenda.”
The civil society agenda item aimed to allow NGOs to attend land COP negotiations, as they do at climate COPs, and included terms of reference for an Indigenous Peoples Caucus.
A representative of Indigenous Peoples told the COP’s closing plenary meeting that the group had “deep disappointment that the agenda of this COP has removed the dedicated space for indigenous peoples”. “We cannot restore the land while removing the voices of those who care for it,” she said.
On Tuesday, the UNCCD’s deputy head Andrea Meza was asked about Indigenous Peoples’ participation. She said that the blocking of “one agenda item” is “generating uncertainty in the progress” towards creating caucuses for Indigenous Peoples and for Local Communities within the talks.
Because of the “complex geopolitical situation” making it hard to obtain consensus, coalitions of the willing have become more important, she added.
Mining out, money in
Outside the formal negotiations, the summit was marked by a focus on the strongly Mongolian issues of the role played by pastoralists and rangelands like grasslands, as well as mining, in both degrading and restoring land.
Part of the conference was sponsored by Australian mining company Rio Tinto and its local partner Oyu Tolgoi. Their presence was protested by campaigners wearing T-shirts calling on the companies to “stop wasting drinking water” and to “get out of Mongolia”.
The UNCDD and others praised the success of the summit in raising more finance for land restoration. The COP saw institutions like the Asian Development Bank and Global Environment Facility pledge money to combat land degradation, with the UNCCD estimating that $645 million of new commitments were made.
An estimated $355 billion a year is needed through 2030 to meet global land restoration commitments, compared with around $77 billion currently invested. Private finance accounts for only around 6% of global investment, according to the UNCCD.
UNCCD chief scientist Baron Orr told a press conference that many of the announcements were public-private partnerships that use government money to “even the playing field” for companies that want to protect land, in a bid to ensure they are not disadvantaged compared with those that do not.
Such partnerships are a “huge opportunity”, he said, especially as “we’re not in a moment of public finance – public finance is tight in every country.”
The post Despite African walkout, fractious land COP ends without drought deal appeared first on Climate Home News.
Despite African walkout, fractious land COP ends without drought deal
Burdened by rising fuel import costs and an “ocean crisis” of record-breaking heat, Pacific island nations are seeking to build support for a new regional fund ahead of COP31, intended to channel investment into renewable energy, community resilience and ocean protection, experts said.
Leaders from the 18-member Pacific Islands Forum (PIF), including Australia and New Zealand, are expected to issue a call for global pledges to the Pacific Resilience Facility (PRF) at a high-level meeting this coming week in Palau, seeking to build a new model for financing climate action.
The new regional fund was formally launched in May this year and is meant to “serve communities at a community level”, swiftly channelling investments for their projects on the ground, according to Fiji’s assistant minister for foreign affairs, Lenora Qereqeretabua.
“We are expecting pledges for the PRF, and these funds will go to communities that apply,” she told journalists at an online briefing. “We have organised it in such a way that it makes our application processes much, much easier than applying for global funding.”
Qereqeretabua added that she expects that PRF funds will be “utilised by communities to protect themselves from climate change and the effects of climate change.”
The Pacific Islands Forum meeting is expected to shape the region’s priorities ahead of this year’s pre-COP, hosted by Fiji and Tuvalu, and COP31, which will be co-led by Australia and Türkiye.
At COP31, a dedicated session on the climate finance needs of small island states will seek to drive pledges into the PRF. The fund has so far received about $172 million in capital – with about $67 million coming from Australia – and aims to close the year with $500 million.
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Ocean heat and fossil fuel shocks
Leaders from the Pacific will meet in Palau from Sunday amid an “ocean crisis” of record-breaking ocean heat caused by this year’s “super El Niño”, according to Kevin Chand, Pacific ocean policy director at National Geographic’s Pristine Seas conservation project.
Leaders at the PIF are expected to put forward commitments towards new marine protected areas, which will be key for shielding ecosystems from future climate extremes, Chand said. The forum is expected to issue a statement on the need for ocean action at COP31, and announce commitments towards reaching the global goal of protecting 30% of the planet’s land and sea ecosystems by 2030.
Rising ocean heat could lead to food insecurity and lost government earnings in the region, as key fish stocks like tuna start migrating away from their coastline in search of colder waters, said Coral Pasisi, director of climate change and sustainability at the Pacific Community (SPC).
Climate shocks are deepening existing economic pressures, as Pacific nations have spent up to a quarter of their GDP on fossil fuel imports due to the war in Iran, according to a recent report by the University of New South Wales (UNSW) in Australia.
Wesley Morgan, one of the study’s authors, told journalists that partner nations “ought to be putting their money where their mouth is”, and should support the energy transition in the Pacific by covering the upfront costs of switching from polluting diesel to solar power, batteries and electricity grid upgrades.
China keeps Indonesia’s battery dream afloat but future less certain
Given the increase in climate-related shocks and sea-level rise, the PIF should also mention the need to phase out fossil fuel extraction and consumption, said Sindra Sharma, international policy lead at the Pacific Islands Climate Action Network (PICAN).
Last year’s COP30 failed to deliver a global roadmap on transitioning away from fossil fuels, which led to a group of countries – including several Pacific island nations – pursuing their own fossil fuel phase-out summit in Santa Marta, Colombia. Next year’s conference will be hosted by Tuvalu and co-chaired by Ireland, which should also receive backing from the PIF, Sharma said.
Both the chairs of the Santa Marta coalition and the Australian COP31 co-presidency have vowed to continue a push for this topic to be discussed at COP31.
New fund to test allies
As local communities in the Pacific struggle to access global climate funds, the PRF’s planned model for quick, direct disbursements has “very solid and good” intentions, Sharma said, but it will need political and financial backing from donor countries.
“The proof is going to be when the fund actually starts operating and delivering to communities,” she added. “If there is too much bureaucracy in being able to access the funds, for example. These things will have to be scrutinised.”
The facility aims to deliver funds in two categories: one for climate adaptation and “disaster resilience”, and another for social and community resilience that includes areas like community capacity-building, education, data analytics and financial management, among others. It will launch its first call for proposals at the PIF.
Morgan added that Australia will need to “leverage global interests” so that funding is directed to the Pacific Resilience Facility “or else the Pacific won’t be able to trust Australia as a partner”. The country ratified the PRF treaty in May, triggering its entry into force.
“The perception [of Australia] in the region is genuinely divided, and it’s worth being honest about it,” Sharma said, adding that the pre-COP31 in Fiji, which is usually limited to a technical space for negotiations, will determine how meaningful Australia’s advocacy for the Pacific can be.
This time, Pacific nations want to use the pre-COP in early October as an opportunity to demonstrate the challenges their largely low-lying islands face and to advocate for their political priorities, including a renewed global effort to limit global warming to 1.5C by cutting emissions faster and deeper. World leaders are due to visit Tuvalu to experience the frontline of rising sea levels, although Australia and Fiji have yet to confirm who will attend.
“In Bonn, Australia was largely missing on the negotiated outcomes that we so urgently need to see. It’s not enough to get Pacific priorities on the agenda. Agenda placement is not delivery,” Sharma added.
The post Pacific islands seek backing for new regional fund ahead of COP31 appeared first on Climate Home News.
Pacific islands seek backing for new regional fund ahead of COP31
Climate Change
Climate change exposes 580 million children to 20 extra ‘heat-stress days’ every year
More than 40% of children under the age of 10 globally are already experiencing at least 20 additional “heat-stress days” due to climate change.
This is according to a new attribution study, published in Science Advances, which combines climate models with demographic data to assess the age groups and regions that are exposed to the most hot, humid days.
The study finds that children up to the age of nine already face more additional heat-stress days globally as a result of climate change than any other age group.
It adds that south Asia and west Africa are recording the greatest childhood exposure to dangerous levels of humid heat – largely because these regions have a rapidly growing population with the highest proportion of young children.
As the climate warms, children will continue to be more exposed to heat stress than any other age group, the paper warns.
The lead author of the study tells Carbon Brief that the findings should inform discussions about climate justice, noting that children in developing countries “have contributed the least to historical greenhouse gas emissions”.
Humid heat
High temperatures can be deadly. For example, the heatwaves that swept across Europe in the summer of 2026 have been linked to tens of thousands of “excess deaths”.
A prominent 2021 study found that children born in the 21st century will be exposed to more extreme weather events in their lifetimes than their parents and grandparents.
Four years later, a study conducted by scientists from the same team found that more than half of children born in 2020 – around 62 million people – will experience “unprecedented lifetime exposure” to heatwaves, even if warming is limited to 1.5C.
Now, the latest research from the same team finds that children already face greater exposure to dangerous levels of humid heat than adults as a result of human-caused climate change.
Extreme heat is particularly dangerous when combined with high humidity. In hot weather, the human body produces sweat to cool itself down. However, as humidity increases, sweating becomes less effective.
The study uses wet-bulb globe temperature – a measure of temperature that takes humidity and wind into account – to calculate heat stress. It defines a “heat-stress day” as any day with a wet-bulb globe temperature above 28C, as this is considered the threshold for “moderate heat stress”
The authors then use climate models to simulate global temperature patterns in the present-day climate. (The authors use the climate of 2023, in which human activity has caused 1.3C of warming, to represent the “present-day”.)
They then count the number of heat-stress days that each country records on average, per year. The authors then repeat this exercise, simulating a pre-industrial climate without human-caused warming.
By comparing the number of heat-stress days in the present-day climate with the number in a pre-industrial climate, the authors can determine how many extra heat-stress days were driven by climate change. They refer to these as “extra” or “attributable” heat-stress days.
The authors find that “low-latitude” countries, located in the tropics, record the most extra heat-stress days.
For example, the paper finds that people living in Côte d’Ivoire currently face 112 heat-stress days every year. It adds that around half of these are due to human-caused climate change.
In contrast, Germany sees only 0.1 heat-stress days per year in today’s climate on average, which is largely attributable to human-caused climate change.
Rosa Pietroiusti, a PhD student at Vrije Universiteit Brussel and lead author on the study, explains why this number may seem lower than expected.
She tells Carbon Brief that the paper “really focuses on humid heat, at levels that are relatively rarely felt in Europe”. She adds:
“Our data also doesn’t capture the urban heat island effect, due to the resolution of the data we use, which also would lead to underestimations of heat stress locally, and lead to a mismatch with what people are experiencing at local scales, particularly in cities.”
Inequality
Extreme heat affects some people more severely than others. Children, people over 65 and those with pre-existing medical conditions or certain disabilities are among the most vulnerable. This is because their bodies are less able to regulate their temperature.
The authors use gridded demographic data to determine the age structure of each country. From this, they calculate how many people from each age cohort are exposed to extra heat days as a result of climate change.
The research finds that globally, 583 million children under the age of 10 already live through at least 20 attributable heat days every year. This accounts for 44% of all children in this age bracket.
In comparison, 190 million people aged 60-69 face at least 20 attributable heat days per year, accounting for 30% of this age cohort.
The authors find that children face the greatest exposure to humid heat for two main reasons.
First, there are more young people alive today than older people, with 1.3 billion children aged under 10 in the world, compared to 0.6 billion people aged 60-69.
Second, they find that countries in Africa and Asia typically have rapidly growing populations with more young children. In contrast, many countries in the northern hemisphere – which are typically cooler – have older populations.
The map below shows how many extra stress heat days each country currently faces as a result of human-caused climate change. Darker reds indicate a higher number of attributable heat days. The blue circles show the percentage of the population under the age of 10, with larger circles indicating a higher percentage.
Warming world
The authors also repeat their analysis for a 1.5C and 2C warmer world. They use population estimates from the SSP2 scenario, which projects that the world’s population will peak at more than nine billion in the second half of the 21st century, with most growth occurring in low-latitude regions – especially in sub-Saharan Africa.
The research finds that, in today’s climate, 11% of all under 10s currently experience 100 or more extra heat-stress days per year due to climate change. In worlds warmed by 1.5C and 2C, the percentage rises to 13% and 23%, respectively.
In contrast, only 6% of all people aged 60-69 currently face 100 or more extra heat-stress days each year due to climate change. This number rises to 9% and 17% for 1.5C and 2C worlds, respectively.
These results are shown in the plot below. The three rows represent the climates of 2023 (top), a 1.5C world (middle) and a 2C world (bottom). The columns show different age cohorts, from the oldest on the left to the youngest on the right.
Each circle contains 100 coloured dots, with each dot representing 1% of the age cohort.
The colour of the dot represents exposure to annual heat-stress day, with darker dots indicating more heat-stress days. Grey dots mean that people experience fewer than one extra heat-stress day per year due to human-caused climate change, while black dots mean more than 150 extra heat-stress days due to climate change.
The figure shows that higher warming levels expose more people to heat stress and that younger cohorts tend to be worst affected.
For example, the top-right circle represents heat stress for under 10s in the present-day climate. Three of these dots are coloured black, indicating that 3% faced at least 150 attributable heat-stress days in 2023.
Pietroiusti tells Carbon Brief the study uses wet-bulb temperature because it is a “well-established heat stress metric”. However, she notes that it was not “explicitly defined to focus on children”. She continues:
“A really important step forward in the research community would be to link up climate science and health science experts to do research on what metrics are really most representative of, for example, health impacts and educational impacts that children will be suffering.”
Vulnerability
Dr Qinqin Kong, a postdoctoral researcher at the departments of medicine and health policy at Stanford University, who was not involved in the study, praises its “robust” methodology.
He tells Carbon Brief that the research provides “a timely quantitative evidence for discussions of climate justice, children’s rights and intergenerational equity”.
However, Kong suggests that the paper “may overstate the contrast between children and the elderly and underestimate the relative burden of older adults”.
He says:
“The elderly may also be more vulnerable due to their social circumstances. Children often benefit from parental supervision and caregiving, whereas many older adults live alone, have limited mobility and face barriers to accessing cooling or emergency assistance during heat events.”
Kong also notes that “people and societies in the mid-latitudes [for example, across much of Europe and North America] are less adapted to heat”, which may make them vulnerable to its impacts.
For example, he says that Europe “shows substantially stronger relative risk of heat mortality likely due to less heat-acclimatised populations, lower air conditioning prevalence and urban designs that don’t favour heat dissipation”.
Similarly, Dr Daniel Vecellio – a researcher at the University of Nebraska, who was not involved in the study – tells Carbon Brief that children are an “understudied cohort”.
However, he says there is “reason for hope” because “children are typically pretty good behavioural adapters to extreme heat” and because people who are “chronically exposed to extreme heat” will “have a better chance at better acclimatisation”.
Pietroiusti tells Carbon Brief that global reporting on heatwaves is often skewed towards wealthier nations.
For example, she notes that large-scale databases of disasters, such as EM-DAT, often underrepresent heatwaves in Africa, due in part to a lack of news coverage and formal reporting. She adds:
“Studies like this, which start from the climate data, can start to fill some of these gaps.”
She adds that the paper should inform discussions about climate justice, noting that children in developing countries, who are most severely affected by the increase in heat-stress days, “have contributed the least to historical greenhouse gas emissions”.
Pietroiusti, R. et al. (2026) Age-specific exposure to human-induced increases in humid heat, Science Advances, doi:10.1126/sciadv.aeb3232
The post Climate change exposes 580 million children to 20 extra ‘heat-stress days’ every year appeared first on Carbon Brief.
Climate change exposes 580 million children to 20 extra ‘heat-stress days’ every year
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