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.
Climate Change
The 2026 budget test: Will Australia break free from fossil fuels?
In 2026, the dangers of fossil fuel dependence have been laid bare like never before. The illegal invasion of Iran has brought pain and destruction to millions across the Middle East and triggered a global energy crisis impacting us all. Communities in the Pacific have been hit especially hard by rising fuel prices, and Australians have seen their cost-of-living woes deepen.
Such moments of crisis and upheaval can lead to positive transformation. But only when leaders act with courage and foresight.
There is no clearer statement of a government’s plans and priorities for the nation than its budget — how it plans to raise money, and what services, communities, and industries it will invest in.
As we count down the days to the 2026-27 Federal Budget, will the Albanese Government deliver a budget for our times? One that starts breaking the shackles of fossil fuels, accelerates the shift to clean energy, protects nature, and sees us work together with other countries towards a safer future for all? Or one that doubles down on coal and gas, locks in more climate chaos, and keeps us beholden to the whims of tyrants and billionaires.
Here’s what we think the moment demands, and what we’ll be looking out for when Treasurer Jim Chalmers steps up to the dispatch box on 12 May.
1. Stop fuelling the fire
2. Make big polluters pay
3. Support everyone to be part of the solution
4. Build the industries of the future
5. Build community resilience
6. Be a better neighbour
7. Protect nature
1. Stop fuelling the fire

In mid-April, Pacific governments and civil society met to redouble their efforts towards a Fossil Fuel Free Pacific. Moving beyond coal, oil and gas is fundamental to limiting warming to 1.5°C — a survival line for vulnerable communities and ecosystems. And as our Head of Pacific, Shiva Gounden, explained, it is “also a path of liberation that frees us from expensive, extractive and polluting fossil fuel imports and uplifts our communities”.
Pacific countries are at the forefront of growing global momentum towards a just transition away from fossil fuels, and it is way past time for Australia to get with the program. It is no longer a question of whether fossil fuel extraction will end, but whether that end will be appropriately managed and see communities supported through the transition, or whether it will be chaotic and disruptive.
So will this budget support the transition away from fossil fuels, or will it continue to prop up coal and gas?
When it comes to sensible moves the government can make right now, one stands out as a genuine low hanging fruit. Mining companies get a full rebate of the excise (or tax) that the rest of us pay on diesel fuel. This lowers their operating costs and acts as a large, ongoing subsidy on fossil fuel production — to the tune of $11 billion a year!
Greenpeace has long called for coal and gas companies to be removed from this outdated scheme, and for the billions in savings to be used to support the clean energy transition and to assist communities with adapting to the impacts of climate change. Will we see the government finally make this long overdue change, or will it once again cave to the fossil fuel lobby?
2. Make big polluters pay

While our communities continue to suffer the escalating costs of climate-fuelled disasters, our Government continues to support a massive expansion of Australia’s export gas industry. Gas is a dangerous fossil fuel, with every tonne of Australian gas adding to the global heating that endangers us all.
Moreover, companies like Santos and Woodside pay very little tax for the privilege of digging up and selling Australians’ natural endowment of fossil gas. Remarkably, the Government currently raises more tax from beer than from the Petroleum Resource Rent Tax (PRRT) — the main tax on gas profits.
Momentum has been building to replace or supplement the PRRT with a 25% tax on gas exports. This could raise up to $17 billion a year — funds that, like savings from removing the diesel tax rebate for coal and gas companies, could be spent on supporting the clean energy transition and assisting communities with adapting to worsening fires, floods, heatwaves and other impacts of climate change.
As politicians arrive in Canberra for budget week, they will be confronted by billboards calling for a fair tax on gas exports. The push now has the support of dozens of organisations and a growing number of politicians. Let’s hope the Treasurer seizes this rare window for reform.
3. Support everyone to be part of the solution
As the price of petrol and diesel rises, electric vehicles (EVs) are helping people cut fuel use and save money. However, while EV sales have jumped since the invasion of Iran sent fuel prices rising, they still only make up a fraction of total new car sales. This budget should help more Australians switch to electric vehicles and, even more importantly, enable more Australians to get around by bike, on foot, and on public transport. This means maintaining the EV discount, investing in public and active transport, and removing tax breaks for fuel-hungry utes and vans.
Millions of Australians already enjoy the cost-saving benefits of rooftop solar, batteries, and getting off gas. This budget should enable more households, and in particular those on lower incomes, to access these benefits. This means maintaining the Cheaper Home Batteries Program, and building on the Household Energy Upgrades Fund.
4. Build the industries of the future

If we’re to transition away from fossil fuels, we need to be building the clean industries of the future.
No state is more pivotal to Australia’s energy and industrial transformation than Western Australia. The state has unrivaled potential for renewable energy development and for replacing fossil fuel exports with clean exports like green iron. Such industries offer Western Australia the promise of a vibrant economic future, and for Australia to play an outsized positive role in the world’s efforts to reduce emissions.
However, realising this potential will require focussed support from the Federal Government. Among other measures, Greenpeace has recommended establishing the Australasian Green Iron Corporation as a joint venture between the Australian and Western Australian governments, a key trading partner, a major iron ore miner and steel makers. This would unite these central players around the complex task of building a large-scale green iron industry, and unleash Western Australia’s potential as a green industrial powerhouse.
5. Build community resilience
Believe it or not, our Government continues to spend far more on subsidising fossil fuel production — and on clearing up after climate-fuelled disasters — than it does on helping communities and industries reduce disaster costs through practical, proven methods for building their resilience.
Last year, the Government estimated that the cost of recovery from disasters like the devastating 2022 east coast floods on 2019-20 fires will rise to $13.5 billion. For contrast, the Government’s Disaster Ready Fund – the main national source of funding for disaster resilience – invests just $200 million a year in grants to support disaster preparedness and resilience building. This is despite the Government’s own National Emergency Management Agency (NEMA) estimating that for every dollar spent on disaster risk reduction, there is a $9.60 return on investment.
By redirecting funds currently spent on subsidising fossil fuel production, the Government can both stop incentivising climate destruction in the first place, and ensure that Australian communities and industries are better protected from worsening climate extremes.
No communities have more to lose from climate damage, or carry more knowledge of practical solutions, than Aboriginal and Torres Strait Islander peoples. The budget should include a dedicated First Nations climate adaptation fund, ensuring First Nations communities can develop solutions on their own terms, and access the support they need with adapting to extreme heat, coastal erosion and other escalating challenges.
6. Be a better neighbour
The global response to climate change depends on the adequate flow of support from developed economies like Australia to lower income nations with shifting to clean energy, adapting to the impacts of climate change, and addressing loss and damage.
Such support is vital to building trust and cooperation, reducing global emissions, and supporting regional and global security by enabling countries to transition away from fossil fuels and build greater resilience.
Despite its central leadership role in this year’s global climate negotiations, our Government is yet to announce its contribution to international climate finance for 2025-2030. Greenpeace recommends a commitment of $11 billion for this five year period, which is aligned with the global goal under the Paris Agreement to triple international climate finance from current levels.
This new commitment should include additional funding to address loss and damage from climate change and a substantial contribution to the Pacific Resilience Facility, ensuring support is accessible to countries and communities that need it most. It should also see Australia get firmly behind the vision of a Fossil Fuel Free Pacific.
7. Protect nature

There is no safe planet without protection of the ecosystems and biodiversity that sustain us and regulate our climate.
Last year the Parliament passed important and long overdue reforms to our national environment laws to ensure better protection for our forests and other critical ecosystems. However, the Government will need to provide sufficient funding to ensure the effective implementation of these reforms.
Greenpeace has recommended $500 million over four years to establish the National Environment Agency — the body responsible for enforcing and monitoring the new laws — and a further $50 million to Environment Information Australia for providing critical information and tools.
Further resourcing will also be required to fulfil the crucial goal of fully protecting 30% of Australian land and seas by 2030. This should include $1 billion towards ending deforestation by enabling farmers and loggers to retool away from destructive practices, $2 billion a year for restoring degraded lands, $5 billion for purchasing and creating new protected areas, and $200 million for expanding domestic and international marine protected areas.
Conclusion
This is not the first time that conflict overseas has triggered an energy crisis, or that a budget has been preceded by a summer of extreme weather disasters, highlighting the urgent need to phase out fossil fuels. What’s different in 2026 is the availability of solutions. Renewable energy is now cheaper and more accessible than ever before. Global momentum is firmly behind the transition away from fossil fuels. The Albanese Government, with its overwhelming majority, has the chance to set our nation up for the future, or keep us stranded in the past. Let’s hope it makes some smart choices.
The 2026 budget test: Will Australia break free from fossil fuels?
Climate Change
What fossil fuels really cost us in a world at war
Anne Jellema is Executive Director of 350.org.
The war on Iran and Lebanon is a deeply unjust and devastating conflict, killing civilians at home, destroying lives, and at the same time sending shockwaves through the global economy. We, at 350.org, have calculated, drawing on price forecasts from the International Monetary Fund (IMF) and Goldman Sachs, just how much that volatility is costing us.
Even under the IMF’s baseline scenario – a de facto “best case” scenario with a near-term end to the war and related supply chain disruptions – oil and gas price spikes are projected to cost households and businesses globally more than $600 billion by the end of the year. Under the IMF’s “adverse scenario”, with prolonged conflict and sustained price pressures, we estimate those additional costs could exceed $1 trillion, even after accounting for reduced demand.
Which is why we urgently need a power shift. Governments are under growing pressure to respond to rising fuel and food costs and deepening energy poverty. And it’s becoming clearer to both voters and elected officials that fossil dependence is not only expensive and risky, but unnecessary.
People who can are voting with their wallets: sales of solar panels and electric vehicles are increasing sharply in many countries. But the working people who have nothing to spare, ironically, are the ones stuck with using oil and gas that is either exorbitantly expensive or simply impossible to get.
Drain on households and economies
In India, street food vendors can’t get cooking gas and in the Philippines, fishermen can’t afford to take their boats to sea. A quarter of British people say that rising energy tariffs will leave them completely unable to pay their bills. This is the moment for a global push to bring abundant and affordable clean energy to all.
In April, we released Out of Pocket, our new research report on how fossil fuels are draining households and economies. We were surprised by the scale of what we found. For decades, governments have reassured people that energy price spikes are unfortunate but unavoidable – the result of distant conflicts, market forces or geopolitical shocks beyond anyone’s control. But the numbers tell a different story.
What we are living through today is not an energy crisis. It is a fossil fuel crisis. In just the first 50 days of the Middle East conflict, soaring oil and gas prices have siphoned an estimated $158 billion–$166 billion from households and businesses worldwide. That is money extracted directly from people’s pockets and transferred, almost instantly, into fossil fuel company balance sheets. And this figure only captures the immediate impact of price spikes, not the permanent economic drain of fossil dependence. Fossil fuels don’t just cost us once, they cost us over and over again.
First, through our bills. Every time there is a war, an embargo or a supply disruption, fossil fuel prices surge. For ordinary people, this means higher costs for energy, transport and food. Many Global South countries have little or no fiscal space to buffer the shock; instead, workers and families pay the price.
Second, through our taxes. Governments around the world continue to pour vast sums of public money into fossil fuel subsidies. These are often justified as a way to protect the most vulnerable at the petrol pump or in their homes. But in reality, the benefits are overwhelmingly captured by wealthier households and corporations. The poorest 20% receive just a fraction of this support, while public finances are drained.
Third, through climate impacts. New research across more than 24,000 global locations gives a granular account of the true costs of extreme heat, sea level rise and falling agricultural yields. Using this data to update IMF modelling of the social cost of carbon, we found that fossil fuel impacts on health and livelihoods amount to over $9 trillion a year. This is the biggest subsidy of all, because these massive and mounting costs are not charged to Big Oil – they are paid for by governments and households, with the poorest shouldering the lion’s share.
Massive transfer of wealth to fossil fuel industry
Adding up direct subsidies, tax breaks and the unpaid bill for climate damages, the total transfer of wealth from the public to the fossil fuel industry amounts to $12 trillion even in a “normal” year without a global oil shock. That’s more than 50% higher than the IMF has previously estimated, and equivalent to a staggering $23 million a minute.
The fossil fuel industry has become extraordinarily adept at profiting from instability. When conflict drives up prices, companies do not lose, they gain. In the current crisis, oil producers and commodity traders are on track to secure tens of billions of dollars in additional windfall profits, even as households face rising bills and governments struggle to manage the fallout.
Fossil fuel crisis offers chance to speed up energy transition, ministers say
This growing disconnect is impossible to ignore. Investors are advised to buy into fossil fuel firms precisely because of their ability to generate profits in times of crisis. Meanwhile, ordinary people are told to tighten their belts.
In 2026, unlike during the oil shocks of the 1970s, clean energy is no longer a distant alternative. Now, even more than when gas prices spiked due to Russia’s invasion of Ukraine in 2022, renewables are often the cheapest option available. Solar and wind can be deployed quickly, at scale, and without the volatility that defines fossil fuel markets.
How to transition from dirty to clean energy
The solutions are clear. Governments must implement permanent windfall taxes on fossil fuel companies to ensure that extraordinary profits generated during crises are redirected to support households. These revenues can be used to reduce energy bills, invest in public services, and accelerate the rollout of clean energy.
Second, we must shift subsidies away from fossil fuels and towards renewable solutions, particularly those that can be deployed quickly and equitably, such as rooftop and community solar. This is not just about cutting emissions. It is about building a more stable, fair and resilient energy system.
Finally, we need binding plans to phase out fossil fuels altogether, replacing them with homegrown renewable energy that can shield economies from future shocks. Because what the current crisis has made clear is this: as long as we remain dependent on fossil fuels, we remain vulnerable – to conflict, to price volatility and to the escalating impacts of climate change.
The true price of fossil fuels is no longer hidden. It is visible in rising bills, strained public finances and communities pushed to the brink. And it is being paid, every day, by ordinary people around the world.
It’s time for the great power shift.
Full details on the methodology used for this report are available here.
The Great Power Shift is a new campaign by 350.org global campaign to pressure governments to bring down energy bills for good by ending fossil fuel dependence and investing in clean, affordable energy for all


The post What fossil fuels really cost us in a world at war appeared first on Climate Home News.
Climate Change
Traditional models still ‘outperform AI’ for extreme weather forecasts
Computer models that use artificial intelligence (AI) cannot forecast record-breaking weather as well as traditional climate models, according to a new study.
It is well established that AI climate models have surpassed traditional, physics-based climate models for some aspects of weather forecasting.
However, new research published in Science Advances finds that AI models still “underperform” in forecasting record-breaking extreme weather events.
The authors tested how well both AI and traditional weather models could simulate thousands of record-breaking hot, cold and windy events that were recorded in 2018 and 2020.
They find that AI models underestimate both the frequency and intensity of record-breaking events.
A study author tells Carbon Brief that the analysis is a “warning shot” against replacing traditional models with AI models for weather forecasting “too quickly”.
AI weather forecasts
Extreme weather events, such as floods, heatwaves and storms, drive hundreds of billions of dollars in damages every year through the destruction of cropland, impacts on infrastructure and the loss of human life.
Many governments have developed early warning systems to prepare the general public and mobilise disaster response teams for imminent extreme weather events. These systems have been shown to minimise damages and save lives.
For decades, scientists have used numerical weather prediction models to simulate the weather days, or weeks, in advance.
These models rely on a series of complex equations that reproduce processes in the atmosphere and ocean. The equations are rooted in fundamental laws of physics, based on decades of research by climate scientists. As a result, these models are referred to as “physics-based” models.
However, AI-based climate models are gaining popularity as an alternative for weather forecasting.
Instead of using physics, these models use a statistical approach. Scientists present AI models with a large batch of historical weather data, known as training data, which teaches the model to recognise patterns and make predictions.
To produce a new forecast, the AI model draws on this bank of knowledge and follows the patterns that it knows.
There are many advantages to AI weather forecasts. For example, they use less computing power than physics-based models, because they do not have to run thousands of mathematical equations.
Furthermore, many AI models have been found to perform better than traditional physics-based models at weather forecasts.
However, these models also have drawbacks.
Study author Prof Sebastian Engelke, a professor at the research institute for statistics and information science at the University of Geneva, tells Carbon Brief that AI models “depend strongly on the training data” and are “relatively constrained to the range of this dataset”.
In other words, AI models struggle to simulate brand new weather patterns, instead tending forecast events of a similar strength to those seen before. As a result, it is unclear whether AI models can simulate unprecedented, record-breaking extreme events that, by definition, have never been seen before.
Record-breaking extremes
Extreme weather events are becoming more intense and frequent as the climate warms. Record-shattering extremes – those that break existing records by large margins – are also becoming more regular.
For example, during a 2021 heatwave in north-western US and Canada, local temperature records were broken by up to 5C. According to one study, the heatwave would have been “impossible” without human-caused climate change.
The new study explores how accurately AI and physics-based models can forecast such record-breaking extremes.
First, the authors identified every heat, cold and wind event in 2018 and 2020 that broke a record previously set between 1979 and 2017. (They chose these years due to data availability.) The authors use ERA5 reanalysis data to identify these records.
This produced a large sample size of record-breaking events. For the year 2020, the authors identified around 160,000 heat, 33,000 cold and 53,000 wind records, spread across different seasons and world regions.
For their traditional, physics-based model, the authors selected the High RESolution forecast model from the Integrated Forecasting System of the European Centre for Medium-Range Weather Forecasts. This is “widely considered as the leading physics-based numerical weather prediction model”, according to the paper.
They also selected three “leading” AI weather models – the GraphCast model from Google Deepmind, Pangu-Weather developed by Huawei Cloud and the Fuxi model, developed by a team from Shanghai.
The authors then assessed how accurately each model could forecast the extremes observed in the year 2020.
Dr Zhongwei Zhang is the lead author on the study and a researcher at Karlsruhe Institute of Technology. He tells Carbon Brief that many AI weather forecast models were built for “general weather conditions”, as they use all historical weather data to train the models. Meanwhile, forecasting extremes is considered a “secondary task” by the models.
The authors explored a range of different “lead times” – in other words, how far into the future the model is forecasting. For example, a lead time of two days could mean the model uses the weather conditions at midnight on 1 January to simulate weather conditions at midnight on 3 January.
The plot below shows how accurately the models forecasted all extreme events (left) and heat extremes (right) under different lead times. This is measured using “root mean square error” – a metric of how accurate a model is, where a lower value indicates lower error and higher accuracy.
The chart on the left shows how two of the AI models (blue and green) performed better than the physics-based model (black) when forecasting all weather across the year 2020.
However, the chart on the right illustrates how the physics-based model (black) performed better than all three AI models (blue, red and green) when it came to forecasting heat extremes.

The authors note that the performance gap between AI and physics-based models is widest for lower lead times, indicating that AI models have greater difficulty making predictions in the near future.
They find similar results for cold and wind records.
In addition, the authors find that AI models generally “underpredict” temperature during heat records and “overpredict” during cold records.
The study finds that the larger the margin that the record is broken by, the less well the AI model predicts the intensity of the event.
‘Warning shot’
Study author Prof Erich Fischer is a climate scientist at ETH Zurich and a Carbon Brief contributing editor. He tells Carbon Brief that the result is “not unexpected”.
He adds that the analysis is a “warning shot” against replacing traditional models with AI models for weather forecasting “too quickly”.
The analysis, he continues, is a “warning shot” against replacing traditional models with AI models for weather forecasting “too quickly”.
AI models are likely to continue to improve, but scientists should “not yet” fully replace traditional forecasting models with AI ones, according to Fischer.
He explains that accurate forecasts are “most needed” in the runup to potential record-breaking extremes, because they are the trigger for early warning systems that help minimise damages caused by extreme weather.
Leonardo Olivetti is a PhD student at Uppsala University, who has published work on AI weather forecasting and was not involved in the study.
He tells Carbon Brief that “many other studies” have identified issues with using AI models for “extremes”, but this paper is novel for its specific focus on extremes.
Olivetti notes that AI models are already used alongside physics-based models at “some of the major weather forecasting centres around the world”. However, the study results suggest “caution against relying too heavily on these [AI] models”, he says.
Prof Martin Schultz, a professor in computational earth system science at the University of Cologne who was not involved in the study, tells Carbon Brief that the results of the analysis are “very interesting, but not too surprising”.
He adds that the study “justifies the continued use of classical numerical weather models in operational forecasts, in spite of their tremendous computational costs”.
Advances in forecasting
The field of AI weather forecasting is evolving rapidly.
Olivetti notes that the three AI models tested in the study are an “older generation” of AI models. In the last two years, newer “probabilistic” forecast models have emerged that “claim to better capture extremes”, he explains.
The three AI models used in the analysis are “deterministic”, meaning that they only simulate one possible future outcome.
In contrast, study author Engelke tells Carbon Brief that probabilistic models “create several possible future states of the weather” and are therefore more likely to capture record-breaking extremes.
Engelke says it is “important” to evaluate the newer generation of models for their ability to forecast weather extremes.
He adds that this paper has set out a “protocol” for testing the ability of AI models to predict unprecedented extreme events, which he hopes other researchers will go on to use.
The study says that another “promising direction” for future research is to develop models that combine aspects of traditional, physics-based weather forecasts with AI models.
Engelke says this approach would be “best of both worlds”, as it would combine the ability of physics-based models to simulate record-breaking weather with the computational efficiency of AI models.
Dr Kyle Hilburn, a research scientist at Colorado State University, notes that the study does not address extreme rainfall, which he says “presents challenges for both modelling and observing”. This, he says, is an “important” area for future research.
The post Traditional models still ‘outperform AI’ for extreme weather forecasts appeared first on Carbon Brief.
Traditional models still ‘outperform AI’ for extreme weather forecasts
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