The warming impact of hydrogen has been “overlooked” in projections of climate change, according to authors of the latest “global hydrogen budget”.
The study, published in Nature, is the most comprehensive analysis yet of the global hydrogen cycle, showing how the gas moves between the atmosphere, land and ocean.
Hydrogen has long been recognised as a clean alternative to fossil fuels and an important component of the green energy transition.
However, while hydrogen is not itself a greenhouse gas, rising emissions are “supercharging” the warming effect of methane, the authors say.
Increasing levels of atmospheric hydrogen have led to “indirect” warming of 0.02C over the past decade, the study finds.
The authors say that limiting leaks from future hydrogen fuel projects and rapidly cutting methane emissions will be key to securing benefits from hydrogen as a clean-burning alternative to oil and gas.
The international team of scientists behind the study also produce the annual “global carbon budget”, which saw its 20th edition published last month.
‘Supercharging’ methane
Hydrogen is the lightest and most abundant element in the universe. It is also an explosive gas that contains more energy per unit of weight than fossil fuels.
The gas has long been recognised as a clean alternative to fossil fuels, because it only emits water when burned.
There are many ways to produce hydrogen. It is typically generated in a carbon-intensive process that relies on fossil fuels. However, renewable energy can be used to produce “green hydrogen” with near-zero carbon emissions.
Hydrogen “indirectly” heats the atmosphere through its interactions with other gases. This warming is mainly due to interplay between hydrogen and methane – a potent greenhouse gas that is the second biggest contributor to human-caused global warming after CO2.
This interplay involves molecules in the atmosphere called hydroxyl radicals. These naturally occurring molecules are known as the atmosphere’s “detergents” because they react with certain greenhouse gases, such as methane, converting them into other compounds that do not warm the planet.
Prof Rob Jackson is a scientist at Stanford University and an author on the study. He explains that hydrogen also reacts with hydroxyl radicals, effectively “using up” these detergents and leaving less to react with methane.
This effectively “extends the lifetime” of methane in the atmosphere, Jackson tells Carbon Brief, leading to higher concentrations and greater warming.
There is also a reciprocal effect, where more methane in the atmosphere leads to more hydrogen. This occurs because methane reacts with oxygen in the atmosphere in a process called “oxidation”, which produces hydrogen.
Jackson tells Carbon Brief that interactions between hydrogen and methane have “not really been considered in climate circles”, adding:
“I think people don’t realise that the dominant source of hydrogen in the world today is methane in the atmosphere.”
Overall, the study estimates that increasing levels of hydrogen in the atmosphere led to global warming of 0.02C over 2010-20. This climate impact has been “overlooked”, the researchers say in a press release.
Jackson tells Carbon Brief that although this level of warming “looks fairly small”, it is still “comparable” to the warming caused by emissions of individual countries, such as France.
The hydrogen cycle
The global hydrogen budget brings together a range of observed data and models to quantify sources of hydrogen emissions as well as “sinks”, which absorb the gas from the atmosphere.
The authors find that hydrogen levels in the atmosphere increased from 523 parts per billion (ppb) in 1992 to 543ppb in 2020.
The graphic below shows the main sources (up arrows) and sinks (down arrows) of hydrogen over 2010-20.
As the figure shows, the largest single contributor to rising hydrogen emissions over 2010-20 is from the oxidation of human-produced methane. Methane emissions are on the rise due to human activity, such as from the fossil fuel industry, livestock and waste.
According to the study, 56% of atmospheric hydrogen over 2010-20 was caused by the oxidation of methane and non-methane volatile organic compounds (NMVOCs) reacting with oxygen to produce hydrogen.
(NMVOCs are chemicals that are released naturally from vegetation and more rapidly during wildfires. Human-produced emissions of NMVOCs – for example, from oil refineries or car tailpipes – are also on the rise, according to the study.)
The study also points to leakage from industrial hydrogen production as another driver of rising atmospheric hydrogen levels.
Jackson tells Carbon Brief that hydrogen leakage is on the rise “not because manufacturing is getting dirtier, but because we’re making more hydrogen from coal and natural gas”.
Hydrogen can also be produced as an unintentional byproduct from the combustion of fossil fuels. The study finds that these emissions of hydrogen are decreasing.
At the same time, natural sources of hydrogen emissions have not shown any increasing or decreasing trend over time, the authors say.
One of the largest natural sources of hydrogen is through “nitrogen fixing” – a chemical process in which nitrogen is converted into ammonia, which releases hydrogen as a byproduct. This process locks down nitrogen into the soil and ocean, where it is used by plants and algae to grow.
Meanwhile, hydrogen sinks have “increased in response to rising atmospheric hydrogen” over the past three decades, the study says.
Nearly three-quarters of the global hydrogen sink comes from hydrogen getting trapped in soil – for example, by microbes taking in hydrogen to use for energy, or hydrogen seeping into the soil through diffusion.
Dr Zutao Ouyang is an assistant professor at the University of Harvard and lead author on the study. He tells Carbon Brief that soil uptake is “the main mechanism removing hydrogen from the atmosphere”, but adds that it also has “the greatest uncertainty” because there is “not much long-term data” on this component of the hydrogen budget.
Mapped
Drawing on data including observational measurements and emissions inventories, the authors map the sources and sinks of hydrogen and their relative strength.
The maps below show the sources (top) and sinks (bottom) over 1990-2020, where darker colours indicate a stronger source or sink.
The largest “hotspots” for hydrogen emissions are in “south-east and east Asia”, according to the research. More widely, it says that “tropical regions” contribute about 60% of total hydrogen emissions.
The authors explain that these “hotspots” occur because the oxidation of methane and NMVOCs – processes that happen in the atmosphere and produce hydrogen as a byproduct – happen more quickly at higher temperatures.
They also find that these regions have more vegetation, which leads to higher NMVOC emissions.
For emissions related to human activity, east Asia and North America “contributed the most hydrogen emissions from fossil fuel combustion”, the study says, due to the “intensive fossil fuel use”.
Hydrogen emissions due to nitrogen fixation – when plants draw down nitrogen and release hydrogen as a byproduct – are highest in South America. The report links these emissions to the region’s “extensive cultivation” of crops such as soybeans and peanuts.
Dr Maria Sand is a senior researcher at CICERO and was not involved in the study. She tells Carbon Brief that the paper “provides a valuable and much-needed assessment of the global hydrogen budget”. She adds:
“By better constraining the sources and sinks of hydrogen, this study helps reduce the uncertainty in the climate impact [of hydrogen].”
Dr Nicola Warwick is a researcher at the National Centre for Atmospheric Science and assistant research professor at the University of Cambridge. She tells Carbon Brief that the study “provides an important update to our understanding of the atmospheric hydrogen budget by better constraining the key sources and sinks of hydrogen”.
She adds that better understanding of hydrogen uptake by soil – including how it responds to “climate-driven changes in soil moisture and temperature” – are “essential for reliably assessing the climate impacts of any future changes in hydrogen emissions”.
Study author Jackson tells Carbon Brief that he hopes the study will “prompt people to evaluate some of these emissions and sources and sinks in new ways and new places”.
Hydrogen economy
In the pursuit of net-zero, hydrogen may play an increasingly important role in the global energy system.
There are many ways to produce hydrogen gas. Most hydrogen is currently generated through a process called steam reforming, which brings together fossil gas and steam to produce hydrogen, with CO2 as a by-product.
According to the study, more than 90% of hydrogen produced today uses this “carbon-intensive” method.
However, electricity can be used to split water into hydrogen and oxygen atoms, in a process called electrolysis. If renewable energy is used, hydrogen can be produced and consumed with near-zero carbon emissions.
Hydrogen can be stored, liquified and transported via pipelines, trucks or ships. It can be used to make fertiliser, fuel vehicles, heat homes, generate electricity or drive heavy industry.
This potential hydrogen “economy” is shown in the graphic below. The illustrations, with numbered captions from one to three, show how hydrogen could be made, moved and used
The graphic below, from Carbon Brief’s explainer, illustrates the elements of a potential hydrogen economy.
Jackson tells Carbon Brief that, in his opinion, hydrogen is a “brilliant” choice to replace fossil fuels on-site, for industries such as steel manufacturing. However, he says he is “concerned” about “a hydrogen economy that distributes hydrogen around the world in millions of users”, because there is potential for lots of the gas to leak.
He adds:
“We know that methane leakage is bad. Hydrogen is a smaller molecule than methane. So wherever you have methane and hydrogen together, if methane leaks, hydrogen is likely to leak even more.”
The authors model hydrogen emissions under a range of future warming scenarios over the coming century.
They find that in “low-warming scenarios with high hydrogen usage”, methane emissions are low, limiting the formation of hydrogen via the oxidation of methane. In this instance, changes in atmospheric hydrogen levels depend strongly on leakage.
Meanwhile, in higher-warming scenarios, the authors find that hydrogen use is “relatively low”, but methane emissions remain “largely unmitigated”. In this instance, they find that the additional hydrogen formed through the oxidation of methane can outweigh hydrogen released through leaks.
Overall, the authors suggest that hydrogen could cause additional warming of 0.01-0.05C by the year 2100. Study author Zutao tells Carbon Brief that this additional warming was not included in the climate projections in the last assessment report from the Intergovernmental Panel on Climate Change.
The post Hydrogen emissions are ‘supercharging’ the warming impact of methane appeared first on Carbon Brief.
Hydrogen emissions are ‘supercharging’ the warming impact of methane
Greenhouse Gases
Cropped 17 December 2025: ‘Deadly’ Asia floods; Boosting London’s water birds; UN headwinds
We handpick and explain the most important stories at the intersection of climate, land, food and nature over the past fortnight.
This is an online version of Carbon Brief’s fortnightly Cropped email newsletter. Subscribe for free here. This is the last edition of Cropped for 2025. The newsletter will return on 14 January 2026.
Key developments
UN talks face headwinds
GLOBAL OUTLOOK: A major new report calling for joint action on climate change and biodiversity was published this month at the UN Environment Assembly talks in Nairobi, Kenya, the Associated Press reported. The newswire said that more than 300 scientists from 83 countries contributed to the latest UN Environment Programme (UNEP) global environment outlook report.
‘SHARP DIVISIONS’: However, for the first time ever, countries failed to agree on a “summary for policymakers” to be published alongside the outlook, according to Agence France-Presse. It said that “sharp divisions” prevented countries reaching consensus on the high-level political summary, with “major oil producers Saudi Arabia and the US oppos[ing] references to phasing out fossil fuels”. The newswire added that UNEP chief Inger Andersen called the lack of a summary “regrettable”, but said the “integrity of the report” remained.
NEW AGREEMENTS: Separate to the report, negotiators in Nairobi were also tasked with agreeing on 15 resolutions and two decisions on a wide range of environmental topics, from plastics to the impact of artificial intelligence, forcing them to “work throughout the day and into the night” towards the end of the summit, according to the Earth Negotiations Bulletin (ENB). In the end, countries adopted 11 resolutions, including on protecting coral reefs from climate change, the global management of wildfires and the preservation of glaciers, a second ENB report said.
TURKISH INFLUENCE: Climate Home News reported that Turkey, the country co-hosting the COP31 climate summit next year alongside Australia, “sought to weaken language on climate change in several draft resolutions” being discussed at the talks. The publication said that the nation, often working alongside Saudi Arabia, “pushed to dilute wording on the climate crisis, the science of melting glaciers and the role of young and Indigenous people”. A separate Climate Home News story said that countries agreed to a first-of-its-kind resolution on addressing the environmental effects of AI, but failed to include a reference to examining its “life cycle” impacts.
‘Deadly’ Asia floods
‘NOT NORMAL’: Climate change made the rainfall behind the “deadly” floods and landslides in parts of south Asia earlier this month more likely to occur and more intense, a World Weather Attribution study covered by the Hindustan Times found. Deforestation and rapid urbanisation also contributed to the extreme flooding that killed more than 1,600 people in several countries, including Sri Lanka, Malaysia and Thailand, the newspaper said. The Guardian noted that while monsoon rains often bring flooding, scientists said this level of intensity was “not normal”.
FOREST LOSS: Mongabay looked at how deforestation contributed to the “catastrophic” impacts from Cyclone Senyar, which caused floods and landslides in Sumatra, Indonesia. The outlet said that “decades of deforestation, mining, plantations and peat drainage left watersheds unable to absorb intense rainfall”. Indonesian environmental group WALHI told the Associated Press that deforestation “stripped away natural defences that once absorbed rainfall and stabilised soil”. Gus Irawan Pasaribu, a local government leader in Tapanuli, told Reuters: “If our forests were well-preserved…it would not have been this terrible.”
NATURE IMPACTS: A separate Mongabay article reported on the “extensive” damage caused by Cyclone Ditwah to Sri Lanka’s “biodiversity-rich” central highlands earlier this month. The outlet said that initial assessments have shown disastrous impacts of flooding and landslides in places such as the Knuckles mountain range, a “Unesco-listed biodiversity hotspot”. Meanwhile, the floods that hit Indonesia were an “extinction-level disturbance” for the Tapanuli orangutan – the world’s rarest great ape, scientists told the Guardian.
Spotlight
Building a bird sanctuary at a London reservoir
In this Spotlight, Carbon Brief visits a radical conservation project aiming to reverse a decline in water birds at a Victorian reservoir in north London.
“I’d recommend bringing wellies! It’s very muddy.”
Those were the instructions of Ben MacMillan, an ecologist at the Canal & River Trust, a charity responsible for looking after the UK’s waterways, including canals, reservoirs and towpaths.
On a damp and grey Tuesday morning, he guided Carbon Brief round the back of a playing fields car park in Hendon, north London, past a metal fence reading “no entry” and across ground covered by several inches of mud to the unlikely site of a radical new conservation effort.
The site is at a degraded wetlands on the northern edge of the Welsh Harp reservoir, a large human-made lake capable of holding 400 Olympic-sized swimming pools of water, first established by the Victorians in the 1830s.
In the 1950s, the reservoir was declared one of the UK’s “sites of special scientific interest”, due to its ability to host an unusually large number of species, including breeding waterbirds, such as silvery-grey common terns and elegant great-crested grebes.
Despite the designation, little was done to protect the site from various threats, including the spread of invasive species, increasing urbanisation and pollution from major roads. The reservoir is bordered on one side by the M1, the main motorway from London to northern England, and by the North Circular, part of central London’s busy ring-road, on another.
In the 1980s, a conservation project led by ecologist Leo Batten transformed the site to create new refuges for breeding birds.
However, for the past 40 years, the reservoir has fallen into “mismanagement”, according to MacMillan – with devastating consequences for its wildlife.
In 2022, just two tern chicks were successfully fledged at the reservoir, compared to 44 in 2000, MacMillan said. Great-crested grebe nests have also dropped from 55 in 1987 to 27 in 2022.
Redesigning the landscape
The dramatic decline has spurred the start of a new £400m restoration project, called “wings on water”, which began in October 2025 and will continue for the next three years.
Headed by MacMillan, the project is making radical changes to the landscape of the site in order to create new habitats and breeding spots for its water birds.
MacMillan has contracted the services of restoration specialists Ebsford Environmental, who have used diggers to create a network of channels across the site.
These channels have uncovered a series of islands that can offer birds a safe place to breed, away from predators such as urban foxes and mink, MacMillan said.
As well as dredging the landscape, MacMillan also plans to introduce new micro-ecosystems, such as wildflower meadows, that will eventually form a “patchwork” capable of supporting a wide range of species.
“It’s all about creating a diversity of habitat,” he said. “It might take five or 10 years to develop, but eventually we’ll end up with an amazing complex mosaic of habitats.”
While MacMillan is “very happy” with the progress being made, the project has some issues to contend with.
One of the recently dug channels is contaminated by toxic silt, poisoned by the runoff of petrol from the nearby major roads. If the petrol seeps out of the silt, it could coat the feathers of birds, negatively affecting their health, MacMillan said.
Ninja turtle legacy
The site is also home to a number of invasive species, each with their own impacts.
One animal causing a particular nuisance are red-eared terrapins, a type of omnivorous shelled reptile, similar in appearance to a turtle, that are native to the US.
“They link back to the 1990s Teenage Mutant Ninja Turtle craze,” MacMillan explained. “People bought loads of them. Then they thought: ‘Oh, these are getting a bit big now’ – and decided to release them in their local park.”
Terrapins have a life span of around 40 years, meaning many released on a whim 30 years ago have now established themselves in waterway habitats across the UK.
While terrapins feed on plants, they have also been seen taking chicks and eggs from nesting birds, MacMillan said:
“In an ideal world, we would move them on. But in practice, it’s very difficult to actually catch them.”
As well as restoring the site for the good of birds, the project also aims to improve access to nature for the local community.
The team plans to install a new boardwalk and viewing platform for the public, which they aim to open next year.
“It should provide a really nice space for people to take a walk in a green space, while being able to spot some breeding birds, in a very urbanised area,” MacMillan said.
News and views
NATURE CASH: The ‘Cali Fund’ – which could generate billions of dollars each year for conservation – recently received its first donation of just $1,000, Carbon Brief reported. On 19 November, nine months after the fund launched, UK start-up TierraViva AI put forward the contribution. The company’s chief executive told Carbon Brief that this was an “ice-breaker” aimed to encourage others to pay in. One expert described the contribution as a good “first step”, but said it is now “time for larger actors to step forward”. Large companies in sectors such as pharmaceutical, cosmetic, biotechnology, agribusiness and technology could contribute to the fund.
FARMING LOSSES: UK crop farmers lost more than £800m in 2025 due to poor harvests and “record heat and drought”, the Guardian reported, based on analysis from the Energy and Climate Intelligence Unit (ECIU). Farmers recorded one of the worst harvests on record this year, with production of wheat, oats, spring and winter barley and oilseed rape dropping 20% below the 10-year average. Three of the five worst harvests have occurred since 2020, the newspaper added, quoting the ECIU’s Tom Lancaster: “The evidence suggests that climate impacts are what’s actually driving issues of profitability.” Meanwhile, BBC News reported that the UK government “roll[ed] back” certain nature protection requirements for housing developers in England.
CLIMATE FINANCE: Biodiversity, conservation and anti-desertification programmes in Africa have struggled to fill a “funding vacuum” since the US froze its development aid earlier this year, according to Mongabay. Experts and observers told the outlet they are “increasingly concerned” about the funding gap that “neither Europe nor billionaire philanthropists seem ready to fill”. Amhed Moustapha Mfokeu, a Cameroonian expert in climate finance, told Mongabay that the closure of the US Agency for International Development (USAID) “created a significant gap in funding for climate-related projects”.
SAVING SOILS: Around 70% of countries do not prioritise soil restoration in their national climate plans, a new report covered by EFEVerde found. The report, from the International Union for the Conservation of Nature’s world commission on environmental law and other groups, said that healthier soils can absorb more carbon and help to limit global warming, the outlet noted. Praveena Sridhar from the Save Soil movement wrote in Earth.org that the recent COP30 climate talks in Brazil “regarded [soils] as a sub-component of the agricultural machine, instead of the foundation to agriculture and many other components of terrestrial life”.
TRADE DEAL: The European parliament voted in favour of including measures to “protect European farmers” in a potential trade deal with South American countries, Bloomberg reported. The outlet said the EU is “rushing” this week to finalise the Mercosur deal, which has been negotiated over the past 25 years and aims to boost trade between the EU and Argentina, Brazil, Uruguay and Paraguay. Reuters reported that France and Italy want to delay the vote, with France trying to “form a blocking minority” against the agreement.
XMAS CHEER: Christmas tree farmers in Canada are adapting to climate change impacts such as warmer weather, CBC News reported. Michael Cormack, who owns a tree farm near Toronto, told the outlet: “This year in July, we were averaging over 29C. So we had trees from two to three years ago that just died…Four years ago, we had a tornado here that wiped out a bunch of our stuff.” The outlet also addressed the age-old question of whether a real or artificial christmas tree is more “eco-friendly”, with one tree researcher saying that a real tree bought from a “local farmer” tends to be a lower-emission choice, or re-using an artificial tree for a long time.
Watch, read, listen
KOLAHOI GLACIER: A retreating glacier in Kashmir is “transforming landscapes and communities”, the Guardian said.
FISHY: DeSmog investigated accusations that the world’s largest salmon producer has wielded a “charm offensive” in the Scottish Highlands to distract from its “noisy” and “polluting” fish farms.
LIVING UNDER THREAT: The Associated Press reported on the “steep risks” environmental activists face in Colombia – the “deadliest country in the world” for environmental defenders.
BAMBOO BARRIER: Rivercane – a species of bamboo – could help protect the southern US from future floods, Grist reported.
New science
- Hard coral cover in Caribbean reefs has reduced by almost half since 1980 | Global Coral Reef Monitoring Network and International Coral Reef Initiative
- Three decades of Amazon forest data shows “higher tree mortality during intense droughts” | Nature
- Vertebrate species could face unsuitable conditions across 10-52% of their range by 2100 due to climate and land-use changes | Global Change Biology
In the diary
- 15-19 December: 70th meeting of the Global Environment Facility council | Virtual
Cropped is researched and written by Dr Giuliana Viglione, Aruna Chandrasekhar, Daisy Dunne, Orla Dwyer and Yanine Quiroz. Ayesha Tandon also contributed to this issue. Please send tips and feedback to cropped@carbonbrief.org
The post Cropped 17 December 2025: ‘Deadly’ Asia floods; Boosting London’s water birds; UN headwinds appeared first on Carbon Brief.
Cropped 17 December 2025: ‘Deadly’ Asia floods; Boosting London’s water birds; UN headwinds
Greenland is closing in on three decades of continuous annual ice loss, with 1995-96 being the last year in which the giant ice sheet grew in size.
With another melt season over, Greenland lost 105bn tonnes of ice in 2024-25.
The past year has seen some notable events, including ongoing ice melt into the month of September – well beyond the end of August when Greenland’s short summer typically draws to a close.
In a hypothetical world not impacted by human-caused climate change, ice melt in Greenland would rarely occur in September – and, if it did, it would generally be confined to the south.
In this article, we explore how Greenland’s ice sheets fared over the 12 months to August 2025, including the evidence that the territory’s summer melting season is lengthening.
(For our previous analyses of Greenland’s ice cover, see coverage in 2024, 2023, 2022, 2021, 2020, 2019, 2018, 2017, 2016 and 2015.)
Surface mass balance
The seasons in Greenland are overwhelmingly dominated by winter.
The bitterly cold, dark winter lasts up to ten months, depending on where you are. In contrast, the summer period is generally rather short, starting in late May in southern Greenland and in June in the north, before ending in late August.
Greenland’s annual ice cycle is typically measured from 1 September through to the end of August.
This is because the ice sheet largely gains snow on the surface from September, accumulating ice through autumn, winter and into spring.
Then, as temperatures increase, the ice sheet begins to lose more ice through surface melt than it gains from snowfall, generally from mid-June. The melt season usually continues until the middle or end of August.
Over this 12-month period, scientists track the “surface mass balance” (SMB) of the ice sheet. This is the balance between ice gains and losses at the surface.
To calculate ice gain and losses, scientists use data collected by high-resolution regional climate models and Sentinel satellites.
The SMB does not consider all ice losses from Greenland – we will come to that later – but instead provides a gauge of changes at the surface of the ice sheet.
According to our calculations, Greenland ended the year 2024-25 with an overall SMB of about 404bn tonnes. This is the 15th highest SMB in a dataset that goes back 45 years, exceeding the 1981-2010 average by roughly 70bn tonnes.
This year’s SMB is illustrated in the maps and charts below, based on data from the Polar Portal.
The blue line in the upper chart shows the day-to-day SMB. Large snowfall events become visible as “spikes”. The blue line in the lower chart depicts the accumulated SMB since 1 September 2024. In grey, the long-term average and its variability are shown. For comparison, the red line shows the record-low year of 2011-12.
The map shows the geographic spread of SMB gains (blue) and losses (red) for 2024-25, compared to the long-term average.
It illustrates that southern and north-western Greenland had a relatively wet year compared to the long-term average, while there was mass loss along large sections of the coast, in particular in the south-west. The spikes of snow and melt are clearly visible in the graphs on the right.
Lengthening summer
Scientists have traditionally pinned the start of the “mass balance year” in Greenland to 1 September, given that this is when the ice sheet typically starts to gain mass.
However, evidence has started to emerge of a lengthening of the summer season in Greenland – as predicted some time ago by climate models.
The start of the 2024-25 mass balance year in Greenland saw ice melt continuing into September. This included a particularly unusual spike in ice melt in the northern part of the territory in September as well as all down the west coast.
In a world without human-caused climate change, ice melt in September would be very rare – and generally confined to the south.
Greenland also saw an early start to the summer melt season in 2025. The onset of the melting season, defined as the first of at least three days in a row with melting over more than 5% of the ice sheet, was on 14 May. This is 12 days earlier than the 1981-2025 average.
The maps below show the extent of melt (red shading) across the ice sheet on 24 September 2024 (left) and 20 May 2025 (right). The blue lines in charts beneath show the percentage melt in 2024 (left) and 2025 (right), up to these dates, compared to the 1981-2010 average (grey).
The melt season began with a significant spike of melting across the southern part of the ice sheet. This happened in combination with sea ice breaking up particularly early in north-west Greenland, allowing the traditional narwhal hunt to start much earlier than usual.
Surface melt
The ablation season, which covers the period in the year when Greenland is losing ice, started a little late. The onset of the season – defined as the first of at least three days in a row with an SMB below -1bn tonnes – began on 15 June, which is two days later than the 1981-2010 average.
Overall, during the 2025 summer, a remarkably large percentage of the ice sheet was melting at once. This area was larger than the 1981-2010 average for three and a half months (mid-June to end of September).
In mid-July, melting occurred over a record area. For three days in a row, melting was present over more than 80% of the area of the ice sheet – peaking at 81.2%. This is the highest value in our dataset, which started in 1981.
The red shading in the maps below shows the extent of melting across Greenland on 19 July (left) and 30 September (right) 2025. The charts beneath show the daily extent of melting through 2025 (blue line), up to these dates, compared to the 1981-2010 average.
Snowfall
However, the SMB is not just about ice melt.
There was a lack of snowfall in the early winter months (September to January), particularly in south-east Greenland, which is typically the wettest part of the territory. The months that followed then saw abundant snow, which brought snowfall totals up closer to average by the start of summer.
A cold period at the end of May and in June protected the ice sheet from excessive ice loss. Melt then continued rather weakly until mid-July.
This was followed by strong melting rates in the second half of July and again in mid-August.
Overall, with both ice melt and snowfall exceeding their historical averages for the year as a whole, the SMB of the Greenland ice sheet ended above the 1981-2010 average.
These increases in snowfall and melt are in line with what scientists expect in a warming climate. This is because air holds more water vapour as it warms – leading to more snowfall and rain. Warmer temperatures also lead to more ice melt.
Total mass balance
The surface mass balance is just one component of the “total” mass balance (TMB) of the Greenland ice sheet.
The total mass balance of Greenland is the sum of the SMB, the marine mass balance (MMB) and basal mass balance (BMB). In other words, it brings together calculations from the surface, sides and base of the ice sheet.
The MMB measures the impact of the breaking off – or “calving” – of icebergs, as well as the melting of the front of glaciers where they meet the warm sea water. The MMB is always negative and has increased towards more negative values over the last decades.
BMB refers to ice losses from the base of the ice sheet. This makes a small negative contribution to the TMB.
(The only way for the ice sheet to gain mass is through snowfall.)
The continued mass loss observed in Greenland is primarily due to a weakening of the SMB – caused by rising melt combined with insufficient compensation of lost ice through snowfall.
The figure below shows how much ice the Greenland ice sheet has lost (red) going back to 1987, which includes the SMB (dark blue), MMB (mid blue) and BMB (light blue). The analysis, which uses data from three models, is based on 2021 research published in Earth System Science.
Despite a relatively high SMB, high calving rates meant that Greenland lost 105bn tonnes of ice over the 12-month period.
This means that 2024-25 was the 29th year in a row with a Greenland ice sheet overall mass loss. As the chart shows, Greenland last saw an annual net gain of ice in 1996.
Satellite data
The mass balance of the Greenland ice sheet can also be measured by looking at the Earth’s gravitational field, using data captured by the Grace and Grace-FO satellite missions – a joint initiative from NASA and the German Aerospace Center.
The Grace satellites are twin satellites that follow each other closely at a distance of about 220km, which is why they are nicknamed “Tom and Jerry”. The distance between the two depends on gravity – which is, in turn, related to changes in mass on Earth, including ice loss.
Therefore, the distance between the two satellites, which can be measured very precisely, can be used to calculate loss of mass from the Greenland ice sheet.
Overall, the satellite data reveals that Greenland’s ice sheet lost around 55bn tonnes of ice over the 2024-25 season.
There is reasonably good agreement between the Grace satellite data and the model data, which, as noted above, finds that 105bn tonnes of ice was lost in Greenland over the same period.
However, the alignment of the two datasets – which are fully independent of each other – becomes more clear once a longer time period is considered.
In the 22-year period between April 2002 and May 2024, the Grace data shows that Greenland lost 4,911bn tonnes of ice. The modelling approach, on the other hand, calculates that 4,766bn tonnes of ice was lost.
The figure below shows gain and loss in the total mass of ice of the Greenland ice sheet, calculated using Grace satellite measurements. It reveals that, over the past 23 years, there has been mass loss in the order of several metres along the coasts of Greenland, with the most significant losses seen on the western coast. Over the central parts of the ice sheet, there has been a small mass gain.
The lower figure shows the contribution of Greenland mass change to sea level rise over the last 23 years, according to the satellite data. It illustrates that more than 5,000bn tonnes of ice have been lost over the time period – contributing to roughly 1.5cm of sea level rise.
Warm over Europe and North America, cool over Greenland
As always, the weather systems across the northern hemisphere play a key role in the melt and snowfall that Greenland sees each year.
As in previous years, multiple heatwaves were observed in southern Europe and North America over the summer of 2025.
And, just like in 2024, there was only modest heat in northern Europe – with the notable exception of Arctic Scandinavia – with a comparably cool and rainy July followed by a warmer and sunnier August.
The high-pressure weather systems that bring heatwaves have a wide-ranging impact on weather extremes across the northern hemisphere.
Strong blocking patterns over North America and Europe were repeatedly present in the course of the summer of 2025. In such a blocked flow, the jet stream – fast-moving winds that blow from west to east high in the atmosphere – is shaped like the Greek capital letter Omega (Ω).
The jet stream bulged up to the north over Canada and northern Europe. West and east of these ridges, low pressure troughs were found at both “feet” of the Omega. One of these troughs was located over Greenland (top left panel in next figure).
This resulted in widespread heat near the cores of these high-pressure systems, fuelling fires in several countries, including large wildfires in Canada. Smoke from these wildfires reached Greenland and Europe in late May.
Unlike in previous years, no heavy precipitation events were observed near the “feet” of the Omega.
If the Omega pattern is displaced by half a wavelength, the opposite – warm over Greenland, with cool continents – is also possible.
This circulation pattern occurred in August 2025 and is shown in the top right panel of the figure below. The bottom panel depicts the large temperature variability in May 2025.
The post Guest post: How the Greenland ice sheet fared in 2025 appeared first on Carbon Brief.
Cities around the world are facing more frequent and intense bouts of extreme heat, leading to an increasing focus on the use of air conditioning to keep urban areas cool.
With the UK having experienced its hottest summer on record in 2025, for example, there was a wave of media attention on air conditioning use.
Yet less than 5% of UK homes have air conditioning and those most vulnerable – older adults, low-income households or people with pre-existing health conditions – often cannot afford to install or operate it.
While air conditioning may be appropriate in certain contexts, such as hospitals, community spaces or care homes, it is not the only solution.
Our research as part of the IMAGINE Adaptation project shows that a universal focus on technical solutions risks deepening inequality and has the potential to overlook social, economic and environmental realities.
Instead, to adapt to record temperatures, our research suggests a keener focus on community and equity is needed.
Contextualising urban heat vulnerability
In the UK, heatwaves are becoming more frequent and severe. Moreover, the evidence points to significant disparities in exposure and vulnerability. By 2080, average summer temperatures could rise by up to 6.7C, according to the Met Office.
During the summer of 2023, around 2,295 heat-related deaths occurred across the UK, with 240 in the South West region. Older adults, particularly those over 65, were the most affected, government figures show.
A recent UN Environment Programme report highlights that there is an “urgent” need for adaptation strategies to deal with rising summer heat.
However, our research shows that framing air conditioning as the default solution risks worsening urban heat by increasing emissions and energy bills, as well as missing the opportunity to design more inclusive, human-centred responses to rising temperatures.
Addressing both gradual and extreme heat involves understanding who is most affected, how people move through cities and the role of social networks.
In recognition of this, cities around the world are already developing potential cooling strategies that combine low-emission interventions with community-based care.
Expanding the concept of ‘cool spaces’
In the UK, Bristol City Council is working on a “cool space” initiative with support from the European Research Council-funded project IMAGINE Adaptation.
The initiative aims to identify a network of public spaces that can offer respite during periods of extreme heat. These spaces can potentially include parks, libraries, community centres or even urban farms.
The map below shows how heat vulnerability varies across the city of Bristol, identifying neighbourhoods most at risk from current and future heatwaves.
But what makes a space “cool”? We used surveys, interviews and workshops to collectively come to an understanding of what a cool space means for Bristol communities.
What emerged from our work is that “cool” is about far more than temperature.
Shade, natural ventilation, seating, access to water and toilets all contribute to comfort, but they do not capture the full picture.
Social and cultural factors, such as whether people feel welcome, whether spaces are free to use or whether children can safely reach them, are equally important. For example, we found that while many community spaces are open to the public, people are often unsure whether they can spend time there without having to buy something.
Our research shows that the presence of a café, even unintentionally, can signal that time and space come at a cost. Clear signage, free entry, drinking water and toilets can help people feel that they are welcome to stay.
Additionally, our research highlights that it is important to recognise that public space is not experienced equally by everyone. Some city centre parks, for instance, may be seen as unwelcoming by people who do not drink alcohol or who feel uncomfortable around noise and large groups.
Creating cool spaces that serve the whole community involves understanding these dynamics and exploring more inclusive alternatives.
Connecting adaptation efforts
The importance of understanding the dynamics of adaptation efforts is especially relevant when considering children, as they are often more vulnerable to increasing temperatures.
At Felix Road adventure playground – one of the early pilot sites in Bristol – staff introduced shaded areas, drinking water and ice lollies to support children during hot weather.
However, adaptation does not just happen at individual sites, but between them, as connectivity to the playground by foot or public transport exposes children to the heat and traffic.
This highlights that adaptation to heat is a city-wide concern, as the effectiveness of individual cooling interventions can depend on both the space itself and how it can be accessed and used by vulnerable populations.
Buses and trains can become uncomfortably hot, making travel difficult for those most at risk. Our research suggests that for some, staying home might seem safer, but many lack cooling options.
Early discussions in the cool space trial show this is especially true for older adults, who also seek social contact alongside thermal comfort in community centres. Advice to stay home during heatwaves, without adequate cooling or guidance, therefore risks both physical harm and increased social isolation.
Relational approaches to adaptation
Viewing cooling as a social issue transforms how we approach urban adaptation and, more importantly, climate action.
Air conditioning reduces temperature, but it does not help foster trust or strengthen community ties. Our research shows that a well-designed community space, by contrast, integrates physical comfort with social support.
For example, they offer places where a parent can supervise children safely in water play, where an older adult might be offered a cold drink or a fan, or where people can simply rest without judgment. These small interactions, while often overlooked, can contribute to reducing heat stress, dehydration or social isolation during heatwaves, creating public spaces that are safer and more supportive for heat-vulnerable residents.
Cool spaces can also serve multiple roles. A library may host children’s activities or provide food support, while a community centre might offer advice on home cooling.
These spaces show that strong community relationships are key to real climate action, offering comfort, connection and practical help all in one place.
Our research shows that by embedding care into design, cities can build approaches to adaptation that go beyond temperature control, recognising the diverse needs of their communities.
However, to continue serving this role effectively, community spaces require ongoing support, including adequate funding, staffing and resources. Without such support, their ability to provide safe, welcoming and inclusive cooling environments for the most vulnerable can be limited.
Challenges and trade-offs
Our research finds that imagining “cool” adaptation is not without challenges.
Our reflections from the ongoing work in Bristol highlight the importance of context-sensitive, adaptive strategies that consider how people live and their needs and expectations, without neglecting the urgent demands of climate action and health protection.
What works in one neighbourhood may be unsuitable in another – and success cannot be defined solely by temperature reduction or visitor numbers.
Listening to communities, observing patterns of use and being willing to reconsider early designs through experimentation and learning are arguably essential for interventions that are socially, culturally and environmentally appropriate.
Climate change is already reshaping how cities function and how communities think and behave. Heatwaves are no longer rare events; they are increasingly intense and dangerous.
In this context, air conditioning may have a role in specific settings and for specific reasons, but it is not the sole answer. Our research shows it cannot replace locally grounded, inclusive and relational approaches to adaptation.
Bristol’s “cool spaces” initiative demonstrates that interventions are most likely to be effective when they are accessible, welcoming and build community, providing more than just shade or technical relief.
This requires investment, coordination and time, but also a shift in perspective: cooling is not just a technical challenge, but about how we look after one another and how we collectively imagine our public spaces in a changing climate.
The post Guest post: Why cities need more than just air conditioning for extreme heat appeared first on Carbon Brief.
Guest post: Why cities need more than just air conditioning for extreme heat
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