The Earth’s jet streams play a fundamental role in the speed and direction of weather systems across the world.
This means that they are crucial for understanding extreme weather events and how they will change as the world warms.
Research suggests that upper-level jet-stream winds will accelerate on average as global temperatures rise, but little is known about how their fastest winds – known as “jet streaks” – will change.
In a first-ever study, published in Nature Climate Change, my co-author and I show that fast jet-stream winds will get faster and faster — by around 2% for every degree Celsius the world warms. This means that fast winds will speed up around 2.5 times more than average jet-stream winds.
Furthermore, it means we should anticipate record-breaking jet-stream winds as warming continues.
Our research also reveals that this acceleration occurs because the difference between the density of the air in the tropics and the air at the poles will increase.
While further work will be needed to understand the full impact of our findings, we expect that they will include stronger severe storms and an increase in clear-air turbulence for aircraft passengers.
Fast flowing
The Earth’s jet streams are fast-flowing narrow bands of wind high up in the atmosphere. The fastest jet-stream winds blow from west to east and occur in the upper troposphere, around 10-12 km above the surface.
Jet streams are important because they shape Earth’s surface climate by steering weather systems, and so they can affect where severe weather occurs. For example, the regions around fast upper-level jet-stream winds – called “jet streaks” – have been linked to the occurrence of storms, tornadoes, hail and severe winds.
Jet streams are also key for air travel, providing an ideal tailwind for aircraft. Previous research has established that the average wind speed of the upper-level jet stream increases under climate change. This has the potential knock-on effect of causing more clear-air turbulence for aircraft passengers.
Our research was inspired by reports in 2019 of transatlantic flights breaking speed records. As a result, we set out to find out how climate change will affect fast jet-stream winds.
Little is known about how fast upper-level jet-stream winds – classed as those above the 99th percentile – could change as the world warms. Furthermore, no mechanism has been proposed to explain why fast jet-stream winds would change.
Fast-get-faster response
We started by examining how physics-based climate models project fast jet-stream winds would change. We used models from the sixth Coupled Model Intercomparison Project (CMIP6), which were developed for the latest assessment by the Intergovernmental Panel on Climate Change (IPCC).
In these model projections, we compare daily jet-stream winds that exceed the 99th percentile at the end of the 20th (1980-2000) and 21st (2080-2100) centuries under a very high emissions scenario (SSP5-8.5). We also compare wind speeds for the near-term in an intermediate scenario (SSP2-4.5), which is broadly in line with the trajectory of global emissions today.
Our analysis finds that climate change makes the fastest upper-level jet-stream winds get faster and faster – by about 2% for every degree Celsius the world warms. This means that fast winds will speed up around 2.5 times more than average jet-stream winds.
We refer to this as the “fast-get-faster” response and we find the effect in all seasons of the year.
You can see this in the chart below, which shows the percentage change in the fastest winds at around 12km altitude per degree of warming across different latitudes (from 80 degrees south on the left-hand side to 80 degrees north on the right).
While the fast winds increase at all latitudes, those in the “extratropics” – that is, between around 20 to 60 degrees, where jet streams are found – are the fastest to begin with and thus get the largest boost under climate change.
Percentage changes in fast (>99th percentile) winds at 200 hectopascal (hPa), normalised by the global average change in surface air temperature for each climate model from 80 degrees south to 80 degrees north in latitude. Simulations use SSP5-8.5. The black line indicates the multi-model average and the shading indicates one standard deviation of the response across all the models. Source: Shaw & Miyawaki (2023)
Moist air
In addition to quantifying the “signal” of long-term change, we also provide a physical explanation for why it occurs.
Bridging the gap between simulating the response to climate change using models and understanding the causes helps us justify that this is a signal to take seriously.
The first step we take is to simplify the model to help isolate what physics underlies the signal. When the model is run without ocean currents and without land, we still find the signal.
This suggests that the fast-get-faster signal emerges in a world formed entirely of water. The result implies that the physics of a moist atmosphere is key to explaining the fast-get-faster response.
The second step we take is to use our physical understanding of the jet stream to quantify the connection between moisture and the signal.
The jet stream exists because of the contrast of density between air at the equator, which is warm and light, and air at the pole, which is cold and dense. We connect this contrast to the response of moisture under climate change.
In particular, in today’s climate, tropical air holds more moisture than air at the poles because it is warmer. Climate change exacerbates this contrast because hotter air can hold much more moisture than colder air.
While the air at the poles is warming more rapidly than in the tropics, hotter air can hold so much more moisture than cold air that the overall density difference still increases.
This effect increases the density contrast under climate change, accelerating the jet-stream winds. Importantly, the effect is multiplicative – namely, fast jet-stream winds today that involve a steep density contrast would be boosted much more in the future than slower jet-stream winds that involve a shallower density contrast.
Thus, our results project record-breaking jet-stream winds.
Emerging signal
When we look at the recent past (1980–2022) using reanalysis data – which combines physical observations with model simulations – we do not find that the fast-get-faster signal has yet emerged from the noise of natural variability.
However, all the climate models in our study suggest that a statistically significant fast-get-faster signal will emerge for the extratropics in both the southern and northern hemispheres by the middle of this century.
Specifically, under SSP2-4.5, all climate models project the signal in the southern and northern hemispheres extratropics by 2038 and 2048, respectively. Under SSP5-8.5, this is slightly earlier – by 2035 and 2045, respectively.
This is shown in the figures below, which show the percentage change in fast jet-stream winds, relative to 1980-2000, from 1980 to 2050 in the southern (top) and northern (bottom) hemispheres, excluding the tropics. The lines indicate reanalysis data (black) and climate models projections under SSP2-4.5 (green) and SSP5-8.5 (orange).
The charts on the right-hand side show the trend, per degree of warming, for each model (green and orange) and the reanalysis data (black). Closed and open circles indicate results that are and are not statistically significant, respectively.
Timeseries of percentage changes (relative to 1980-2000) in fast 200hPa jet-stream winds in reanalysis and climate models for different emission scenarios for the southern (top) and northern (bottom) hemisphere extratropics from 1980 to 2050. Data are presented as multi-model average (thick line) with one standard deviation of the response across the models (shading). Right-hand charts show the linear trends of these changes per degree of global warming, where statistically significant trends are indicated by closed circles. Source: Shaw & Miyawaki (2023)
We are now working to better understand the knock-on impacts of these changes in the jet stream for severe weather.
New climate models are allowing scientists to look in greater detail at how extreme weather is – and will – change. Ultimately, unravelling the impacts of climate change on winds at regional scales will help society better prepare for the implications of a warming world.
The post Guest post: Why ‘jet-streak’ winds will get faster as the climate warms appeared first on Carbon Brief.
Guest post: Why ‘jet-streak’ winds will get faster as the climate warms
Confusion reigned in Antalya on Wednesday morning as some delegates heeded the Turkish organisers’ warning to get to the COP31 venue before 7am today. Others saw a later UN clarification that this wasn’t necessary, and many more decided not to chance it and work from their hotel rooms.
Additional restrictions seem to have been put in place so that the 40 or so world leaders due to speak could be ferried from the airport to the venue and so that President Recep Tayyip Erdoğan could plant some symbolic olive trees without ordinary COP delegates ruining the photo op.
The list of world leaders speaking today is considerably shorter than the (already short) list from just six days ago, with the leaders of Nigeria, Kenya, Egypt, the Netherlands and Sweden among those dropping out.
Still on there are the co-hosts Erdoğan and Australia’s Albanese plus Brazil’s recently re-elected President Lula and the European Commission head Ursula Von der Leyen. The leader of rainforest-rich DR Congo and the vice president of clean energy and coal superpower China will also speak, as well Barbados’s Mia Mottley and Saudi Arabia’s energy minister Abdulaziz bin Salman.
While the leaders of big-emitting countries have not turned up, there will be plenty of voices from the frontlines of climate change with heads of government from desertifying Mauritania, water-stressed Iraq, the sinking Marshall Islands and drought-hit Somalia all speaking.
Today is also “Zero Waste” Day, with First Lady Emine Erdoğan holding an afternoon roundtable on her pet topic. Before COP, Climate Home News visited a landfill and zero waste education centre in Ankara to find out how well – or otherwise – Türkiye is doing in its pursuit of waste reduction.
Türkiye pushes “zero waste” at COP31, but is it delivering at home?
We’re watching out for any news on the country’s single-use plastics ban, which has been introduced to parliament but not yet – after some lobbying from the plastics industry – got the president’s signature.
The post COP31 Bulletin Day 3: With the people stuck outside, world leaders jet in appeared first on Climate Home News.
COP31 Bulletin Day 3: With the people stuck outside, world leaders jet in
The amount of public funding pledged to help developing countries tackle climate change has dropped by more than 70% in 2026, according to Carbon Brief analysis.
Developed countries are required under UN climate treaties to provide “climate finance” and have traditionally announced multi-year pledges to feed into their global commitments.
Most of these pledges expired in 2025 and, since then, the US has withdrawn from international climate efforts and many European aid budgets have been cut.
A civil-society tracker shows that only five nations have announced new multi-year pledges, including just one major donor – the UK.
Germany, France and Japan are among the key contributors that have so far failed to set out plans for new climate finance, while none is expected from the US.
As a result, the total amount of public climate finance pledged over the next few years amounts to just $11.7bn a year in spending, down from recent levels of around $40bn.
Experts tell Carbon Brief that global conflict, fiscal constraints and the rise of the far right are all making it harder for developed-country governments to pledge new funds.
As the COP31 summit in Turkey gets underway, developing countries are stressing their urgent need for new finance, after nations agreed to a new global target just two years ago.
Missing pledges
Under the Paris Agreement, developed countries are obliged to provide climate finance to help developing countries cut their emissions and prepare for climate disasters.
This financial assistance can be channelled through multilateral development banks, UN climate funds and investments “mobilised” from the private sector.
But a large chunk is also expected to come directly from the public coffers of developed countries – primarily their foreign-aid budgets. This public spending has made up roughly a third of climate finance flowing to developing countries in recent years.
The EU, the US and others agreed just two years ago that they would “take the lead” on scaling up annual climate finance from $100bn in the early 2020s to $300bn by 2035.
Donor countries have traditionally supported such goals by announcing multi-year targets that indicate how much they plan to spend on climate finance.
Nearly all of these pledges expired in 2025 – and hardly any major donors have announced new ones to replace them, covering the period out to 2030.
This lack of new commitments is captured in a tracker of old and new financial commitments by climate NGOs NRDC and E3G.
Carbon Brief analysis of this data, based on an annualised breakdown of targets, shows that developed countries had previously pledged around £42bn a year in public finance.
As the chart below shows, based on current pledges, this has fallen by around 71% to £11.8bn, on average, over the remainder of the 2020s.
Not all contributors announced public climate-finance pledges in advance for the pre-2026 period. Some did not hit their stated targets, while others exceeded them.
While official data for 2025 is not yet available, bilateral public finance reached £43.9bn in 2024, broadly in line with the amount pledged by developed countries.
Big contributors
International climate finance has been consistently dominated by five nations – Japan, Germany, France, the US and the UK.
These countries – together with the EU – have provided around 90% of all the bilateral, public climate finance going to developing countries in recent years.
Of these key players, only the UK has announced a new pledge, committing £6bn ($8bn) of aid between 2026-27 and 2028-29, plus £6.7bn ($8.9bn) from outside its aid budget.
This accounts for half of all the annual funds pledged from 2026 onwards – averaging $5.7bn a year.
The European Commission makes up most of the remainder, with an average annual contribution of $4.5bn promised out to 2027.
Rather than a new pledge, this is due to the commission promising to spend €28bn ($31.8bn) over its 2021-2027 budget period. Its post-2027 contribution is currently being discussed as part of wider EU budget negotiations.
Canada has promised to spend CA$5.3bn ($4.1bn) by 2030, averaging $860m a year. The Netherlands, Switzerland and Belgium have also pledged relatively small sums.
Overall, despite developed countries committing to scale up climate finance, these new pledges are either less ambitious – or only slightly more ambitious – than previous ones. This can be seen in the chart below.
The UK’s pledge appears more ambitious, but this is because the government has changed how it counts climate finance to include $8.9bn in “additional” public finance. When only the like-for-like aid components are compared, the new pledge amounts to a drop in ambition. (For more details, see the methodology.)
The most significant absence is the US, which committed to reaching $11.4bn in annual support by 2024 under the Biden administration.
Since president Donald Trump took power, the US has – for the second time – withdrawn from the Paris Agreement and shrunk its aid budget. It will not provide any official climate finance in the coming years.
Another notable absence is Australia, which is jointly hosting the upcoming COP31 summit, alongside Turkey. Josie Lee, policy and advocacy lead at Oxfam Australia, tells Carbon Brief:
“If Australia fails to announce a climate-finance pledge as president of negotiations, it would send a problematic message to those resisting action on climate change that might serve to embolden their agenda.”
Japan is the largest overall contributor of public climate finance, but it has not traditionally announced targets for this type of spending. Instead, the government set out overall goals that also bundle in finance “mobilised” from the private sector.
As a result, its public-finance ambitions have not been included in this analysis.
So far, the Japanese government has not announced any new multi-year climate-finance pledges, from either the public or the private sector.
European cuts
Europe provides the majority of international climate finance, but European governments have massively cut their aid spending in recent years, citing economic strain and defence spending needs.
Germany and France, the two largest European climate-finance contributors, both pledged to reach €6bn ($6.8bn) per year by 2025. Neither has committed to anything beyond that.
Both nations have slashed their aid budgets in recent years, including funding for climate programmes. Germany missed its 2025 climate-finance goal due to these cuts.
Dr Anja Carolin Gebel, a senior policy advisor at Germanwatch, tells Carbon Brief that this issue has become more politically fraught since the centre-right Christian Democratic Union (CDU) won the 2025 election and began leading a coalition government:
“The issue of climate change – and, subsequently, climate finance – has taken a back seat in the current government coalition.”
There has also been a political shift in France, Gaïa Febvre, international policy coordinator at Réseau Action Climat, tells Carbon Brief. She adds:
“The upcoming presidential election and the growing influence of the far right are likely to make new international financial commitments politically more difficult.”
Other significant European donors are also undergoing political turmoil.
Spain’s centre-left government has triggered a snap election for the end of November, making a new climate-finance pledge during COP31 less likely.
Following a narrow election win, a centre-left bloc in Sweden is still in the process of trying to form a new coalition government.
Some nations have signalled that their climate finance will continue flowing, even though they have not officially set out specific new pledges.
The Dutch government, for example, has said it will provide “at least” €300m ($334m) of specific climate funding annually out to 2031. However, it has also indicated that its total public climate finance is likely to be considerably higher in both 2026 and 2027.
To highlight the lack of new pledges, developing countries are championing a “climate-finance work programme” at COP31, which could provide a space to discuss scaling up public climate finance from developed countries.
In response, the EU has stressed that its member states are the “largest providers” of public climate finance and called on developing countries to submit overdue plans for cutting emissions. The EU and its member states provided a record €32.3bn ($40bn) in 2025.