Every increment of global warming above 1.5C increases the risk of crossing key tipping points in the Earth system – even if the overshoot is only temporary, says new research.
It is well established that if global temperatures exceed 1.5C above pre-industrial levels, there is a higher risk that tipping points will be crossed.
The new study, published in Nature Communications, investigates the risk of crossing four interconnected tipping points under different “policy-relevant” future emissions scenarios.
The authors investigate the risk of tipping where warming temporarily overshoots 1.5C, but global temperatures are then brought back down using negative emissions technologies. They find that the longer the 1.5C threshold is breached, and the higher the peak temperature, the greater the risk of crossing tipping points.
The most pessimistic scenario in the study sees global warming hit 3.3C by the end of the century – in line with the climate policies of 2020 – before dropping back below 1.5C over 2100-2300. Under this pathway, there is a 45% chance of crossing tipping points by 2300, the authors say.
The authors also warn that if global temperatures rise above 2C, the additional risk of tipping for every extra increment of warming “strongly accelerates”.
For temperatures between 1.5C and 2C, the risk increases by 1-1.5% for every 0.1C increase in overshoot temperature. However, for temperatures above 2.5C, tipping risk increases to 3% per 0.1C of overshoot.
The research “underlines the need for urgent emission cuts now that do not assume substantial carbon dioxide removal later”, a scientist not involved in the study tells Carbon Brief.
Overshoot scenarios
Scientists have warned for decades that as the planet warms, there is an increasing risk that Earth systems will cross “tipping points” – critical thresholds that, if exceeded, could push a system into an entirely new state.
For example, if climate change and human-driven deforestation push the Amazon rainforest past a critical threshold, large parts of the forest could experience “dieback”. This would cause entire sections of lush rainforest to eventually shift to dry savannah.
(See Carbon Brief’s explainer on the nine tipping points that could be crossed as a result of climate change.)
The planet has already warmed by 1.3C above pre-industrial levels, and a recent study warned that five tipping elements – including the collapse of the west Antarctic ice sheet – are already within reach.
That study emphasised the importance of limiting global temperature rise to 1.5C above pre-industrial levels – in line with the 2015 Paris Agreement. It finds that warming of 1.5C would render four climate tipping elements “likely” and a further six “possible”. Meanwhile, 13 tipping elements will be either “likely” or “possible” if the planet warms by 2.6C, as expected under current climate policies.
Many of the potential pathways to limiting global temperature rise to 1.5C by 2100 see the planet initially “overshoot” the threshold before negative emissions methods are used to bring temperatures back down.
The new paper investigates 10 future warming scenarios which run to the year 2300. The authors use the PROVIDE v1.2 emission pathways, which they describe as “an extended version of the illustrative pathways identified” used in the recent sixth assessment of the Intergovernmental Panel on Climate Change (IPCC).
The original scenarios run over 2015-2300, but the authors carried them forward for another 50,000 years by following the temperature trajectory set over 2290-2300. All scenarios stabilise at 1.5C, 1C or pre-industrial temperatures. However, many include overshoots, with peak temperatures ranging from 1.57C to 3.30C.
These scenarios show a range of options for how global temperatures change under these 10 scenarios in the “medium term” – until the year 2300 – as well as in the “long term”, which runs 50,000 years into the future to see how the planet eventually stabilises.
Scenarios that reach net-zero or negative emissions by 2100 and maintain them thereafter are classified as “NZGHG emission scenarios”. The table below gives more detail on each scenario.
| Scenario | Overshoot peak temperature | NZGHG | Stabilisation temperature | Scenario assumptions |
|---|---|---|---|---|
| CurPol-OS-1.5C | 3.30C | Never-NZGHG | 1.5C | Follows current (2020) policies until 2100, then declines |
| ModAct-OS-1.5C | 2.69C | Never-NZGHG | 1.5C | Follows current (2020) pledges (NDCs) until 2100, then declines |
| ModAct-OS-1C | 2.69C | Never-NZGHG | 1.0C | Follows current (2020) pledges (NDCs) until 2100, then declines |
| Ref-1p5 | – | not defined | 1.5C | Reference scenario designed in temperature space |
| SSP5-3.4-OS | 2.35C | No-long-term-NZGHG | 1.5C | Tests system response to rapid emission changes |
| SSP1-1.9 | 1.53C | No-long-term-NZGHG | 1.0C | Sustainable development, no long-term compensation of non-CO2 emissions |
| GS-NZGHG | 1.70C | NZGHG | pre-industrial | Gradual strengthening, returns warming to 1.5 °C by 2215 |
| SP-NZGHG | 1.57C | NZGHG | pre-industrial | Broad shift towards sustainable development |
| Neg-NZGHG | 1.67C | NZGHG | pre-industrial | Returns warming to 1.5 °C by 2100 with heavy CDR deployment |
| Neg-OS-OC | 1.67C | NZGHG | pre-industrial | Returns warming to 1.5 °C by 2100 with heavy CDR deployment |
Table showing the 10 scenarios used in this study. Source: Möller et al (2024).
There is quite a range between the 10 pathways.
At the high end, the “CurPol-OS-1.5C” scenario sees a continuation of the global climate policies implemented in 2020 until the year 2100, with warming peaking at 3.3C. It then sees a decline in global temperature until reaching a stabilisation of 1.5C by the year 2300.
At the low end, “Neg-OS-0C” scenario initially overshoots 1.5C to 1.67C, but then returns warming to 1.5C by 2100 using “heavy carbon dioxide removal deployment”. It also then sees average global temperatures drop to pre-industrial levels by the year 2300.
In the middle, the Ref-1p5 scenario is the only one that does not include an overshoot, instead stabilising quickly at 1.5C.
The chart below shows greenhouse gas emissions (top) and corresponding global temperature changes (bottom) associated with each scenario, identified by the different-coloured lines. The bottom chart illustrates the range in how quickly the pathways return to 1.5C or below.
Dr David McKay is a research impact fellow at the University of Exeter’s Global Systems Institute, who has published extensively on climate tipping points, but was not involved in this study.
He also notes that some of the scenarios shown in this study “may not be possible”, because there is debate about whether or not “the substantial carbon dioxide removal needed for large overshoots is feasible”.
Cascades
Many Earth systems are interlinked, so crossing one tipping point can increase the likelihood of crossing others. This is often described as a “domino effect” or “tipping cascade”.
The study focuses on four interconnected tipping points – collapse of the Greenland ice sheet and west Antarctic ice sheet, shutdown of the Atlantic Meridional Overturning Circulation and dieback of the Amazon rainforest.
Annika Högner is a researcher at the Potsdam Institute for Climate Impact Research (PIK) and co-lead author on the study. She tells Carbon Brief these four tipping points were chosen because they “play a significant role in the functioning of the Earth system” and “their tipping would have severe global impacts”.
The graphic below shows how the tipping points interact with each other. A “+” symbol indicates that crossing one tipping point can destabilise another. For example, a collapse of the Greenland ice sheet makes the AMOC more likely to shut down, as a result of the sudden influx of freshwater into the north Atlantic Ocean. A “±” symbol indicates that the relationship between two tipping points is uncertain.
A “-” symbol indicates that crossing one tipping point stabilises another. Högner tells Carbon Brief that the interaction between the Greenland ice sheet and AMOC is the only stabilising interaction in this study. She explains that if the AMOC were to cross a tipping point, “we [would] expect to see strong cooling in the northern hemisphere”, which will contribute to stabilising the Greenland ice sheet.
Earth system models “often don’t resolve tipping processes very well”, making them less suited to modelling full tipping cascades, Högner tells Carbon Brief.
Instead, she explains that the authors developed a “conceptual model”. This model does not attempt to simulate the entire Earth system, but instead just models the likelihood of tipping at different temperatures, based on existing knowledge about tipping elements from other studies.
The model takes temperature trajectories as an input and gives the state of the tipping elements after a specified time – that is, whether or not the element has tipped – as an output.
Importantly, these models include “hysteresis” – a feature of tipping systems, in which a system that has moved to a different state does not easily move back to the original state even if temperatures are reduced again.
Tipping risk
The authors use their conceptual model to calculate “tipping risk” under the 10 future warming scenarios. Högner tells Carbon Brief that tipping risk “refers to the model of all four interacting tipping elements analysed in the study”. For example, a 50% tipping risk means there is a 50% chance that at least one of the four climate elements will tip.
The top row of the graphic below shows the risk of tipping in the year 2300 (left) and in 50,000 years from now (right). Bars placed higher up indicate a greater likelihood of tipping. The dot shows the average value for each data point, while the bars show the 10-90% range.
The text on the right hand side gives likelihood levels in the calibrated language used by the IPCC: very likely means a likelihood of 90-100%, likely is 66-100%, about as likely as not is 33-66%; unlikely is 0-33%; and very unlikely is 0-10%.
The middle row shows the peak temperature under each scenario (left) and stabilisation temperature (right). The bottom row shows how long temperatures overshoot before stabilising in each scenario.
The longer the 1.5C threshold is breached for, and the higher the peak temperature is, the greater the risk of crossing tipping points by the year 2300, the study shows.
The authors find the greatest risk of crossing tipping points in the CurPol-OS-1.5C scenario (red), which follows the climate policies of 2020 until the year 2100 and then reaches 1.5C by 2300, as this scenario has the greatest overshoot temperature and duration.
Under this scenario, there is a 45% tipping risk by 2300 and a 76% chance in 50,000 years, according to the paper.
The five pathways that do not return warming to 1.5C by the year 2100 have the greatest medium-term risks, and those with less than 0.1C overshoot have the lowest medium-term risks.
In the long-term – looking to the next 50,000 years – the authors find that stabilisation temperature is “one of the decisive variables for tipping risks”. They find that even in the Ref1p5 scenario – which sees global temperatures stabilise at 1.5C without any overshoot – there is a 50% risk of the system tipping over the next 50,000 years.
The results “illustrate that a global mean temperature increase of 1.5C is not ‘safe’ in terms of planetary stability, but must be seen as an upper limit”, the study warns.
Högner tells Carbon Brief that the paper “underlines the importance of adhering to the Paris Agreement temperature goal”.
Tessa Möller – a researcher at the International Institute for Applied Systems Analysis (IIASA) and co-lead author on the paper – tells Carbon Brief that “we have a wide portfolio of technologies available” to limit warming to 1.5C, and just need to “implement” them.
However, she also highlights the “large credibility gap” between pledges from individual countries and the policies they have actually implemented. She tells Carbon Brief that not only do we need “stronger pledges”, but it is also essential that countries follow through on them.
Long-term climate
The authors also explore the risk of each individual tipping point being crossed in different scenarios.
The plot below shows the tipping risk by 2300 under different scenarios, at different temperatures, on the left. Each colour represents one scenario. Dots positioned further to the right indicate a greater peak temperature and dots positioned higher up indicate a greater tipping risk.
The plot on the right shows the percentage change in tipping risk for every additional 0.1C of overshoot, for different peak global temperatures, for the Amazon (cross), AMOC (plus), West Antarctic ice sheet (black dot) Greenland Ice sheet (square) and overall (yellow dot).
The authors find that AMOC collapse and Amazon dieback would likely be the first components to tip. This could be in the next 15-300 years and 50-200 years, respectively, depending on the scenario, they find.
Meanwhile, the Greenland and west Antarctic ice sheets have tipping timescales of 1,000-15,000 years and 500-13,000 years, respectively.
However, they note that as temperatures increase, the relative risk of each element tipping changes. The graph shows that while AMOC is the main driver of tipping risk at lower temperatures, the Amazon becomes the main driver once global temperatures exceed 2C.
Finally, they find that as global temperatures rise, the risk of tipping accelerates. Overall, tipping risk increases by 1-1.5% per 0.1C increase in overshoot temperature, for temperatures below 2C, according to the study. However, above 2.5C, tipping risk increases to 3% per 0.1C increase overshoot.
McKay notes that there are some limitations in the study. For example, he notes that the paper “has to rely on tipping threshold and timescale estimates with often wide ranges and sometimes low confidence, while tipping interaction estimates are based on dated expert judgement”.
However, he adds:
“This work makes it clear that every fraction of warming increases the chance of tipping points, even if global temperature subsequently falls, and underlines the need for urgent emission cuts now that do not assume substantial carbon dioxide removal later.”
The post ‘Every 0.1C’ of overshoot above 1.5C increases risk of crossing tipping points appeared first on Carbon Brief.
‘Every 0.1C’ of overshoot above 1.5C increases risk of crossing tipping points
KOROR, PALAU, Friday 4 September 2026 – At the closing of the 55th Pacific Islands Forum Leaders Meeting in Palau overnight, Greenpeace Australia Pacific called out Australia for promising climate action while expanding fossil fuel production, and is urging Pacific leaders to unite ahead of the Pacific Pre-COP.
The meeting was rocked by the UN’s 1.5°C overshoot report a day before Australia approved the extension of one of the country’s largest coal mines.
Speaking from Palau, Shiva Gounden, Head of Pacific at Greenpeace Australia Pacific, said:
“Against the backdrop of the 1.5°C UNEP report, this Forum was a vital opportunity for Pacific leadership to shine by firmly calling out fossil fuels and banding together for our shared Pacific future. While the final communique reaffirmed the need to accelerate the transition away from fossil fuels, Pacific leaders missed the opportunity to hold the Australian government accountable for their continued approval of new coal and gas projects.
“At Pacific Pre-COP in Nadi, we are calling for Pacific priorities to be centred and respected by Australia and our global partners: they must support the ambition of a Fossil Fuel Free Pacific, ensure access to adequate climate finance and lead a global push to hold the line on 1.5°C as a matter of Pacific survival.
“Leaders fell short at the Pacific Islands Forum, and Pacific Pre-COP is the opportunity to match the ambition with urgency, and set the vaka on course toward a peaceful, just Pacific future.”
Speaking from Palau, Dr Simon Bradshaw, COP31 Lead and climate expert at Greenpeace Australia Pacific, said:
“The Pacific Islands Forum was an opportunity for Prime Minister Albanese to show real commitment to climate action and to its Pacific partnership. Instead, this week the Australian Government ‘celebrated’ the first extraction of polluting gas from the Beetaloo Basin and approved an extension of one of Australia’s largest coal mines. All amidst a still unfolding flood crisis in Nepal-Tibet and the devastating news that the world will blow through 1.5°C of warming — a survival line for Pacific communities.
“These are not the actions of a government aspiring to be a global climate leader and effective middle power in turbulent times, they are the actions of a government still beholden to the fossil fuel industry. Australia, get it together.
“As we head towards the Pacific Pre-COP, our Prime Minister and Government must remember the responsibility we have taken on. We must hold the line on returning warming to 1.5°C as our legal and moral obligation. This means doing everything possible to accelerate the global transition away from fossil fuels, starting at home.”
—ENDS—
Australia blows PIF climate opportunity as Pacific leaders urged to band together
As efforts to expand energy access across Africa grow, experts and policymakers have called this week for greater coordination and investment to power food production with renewables, arguing the sector has been treated separately from energy policy and therefore faces barriers in going green.
Hailemariam Desalegn, former prime minister of Ethiopia, said energy is critical across the food value chain – from irrigation and processing to cold storage and transport – and should therefore be considered a key pillar of strengthening food systems for the future.
“Energy is not separate from the nutrition challenge. Irrigation needs energy. Cold storage, transport, processing, as well as markets – all need reliable energy,” Desalegn told a panel at the 20th session of the Africa Food Systems Forum in Kigali. He said investments in sustainable energy systems could help reduce post-harvest losses and make nutritious food more accessible and affordable.
Africa loses up to 30% of its food before it reaches markets annually, largely due to poor roads, weak storage and inadequate cold chains, according to a 2025 report by the Alliance for a Green Revolution in Africa (AGRA).
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Akinyi Walender, Africa director at development charity Practical Action, said poor energy supply in rural communities – where much of Africa’s food is produced – is also limiting productivity. Across the continent, about 600 million people currently live without access to electricity.
“The lack of energy access goes well beyond the inconvenience of not having lighting at home,” Walender said, adding that renewable energy has the potential to power local economies. “When people can access this sort of energy, it can raise rural incomes, improve food security, improve resilience, empower women and stimulate enterprise while creating jobs,” she added.
Breaking down silos
Unlocking the potential of energy across food systems requires greater coordination, Walender argued, pointing to institutional fragmentation and isolated pilot projects as major barriers.
“Organisations working on agriculture and energy often operate according to different modalities and the interdependence between agricultural and energy markets is often overlooked,” Walender said, adding that finance institutions also tend to work in silos.
Dana Rysankova, global lead for energy access at the World Bank, told a separate event at the forum that the bank is working to break down those barriers through its newly established Productive Use of Energy (PUE) Centre of Excellence based in Nairobi, which has a mandate to foster collaboration and help develop and design programmes across different sectors.
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In June, the World Bank Group and the African Development Bank Group said that over 50 million people had been connected to electricity across 40 African countries under their Mission 300 initiative, which aims to provide electricity access to 300 million Africans by 2030.
Rysankova said the programme has shown that energy access is just the foundation for linking with other sectors to deliver real economic transformation by boosting productivity and local incomes.
Mission 300 also aims to electrify schools and healthcare services, as well as bringing power to farmers so that they can use it for irrigation, cold storage and other agricultural activities, she added.
Bridging the finance and infrastructure gap
Experts said bigger investments are needed in infrastructure and finance to turn energy access into increased productivity and economic value.
AGRA’s 2026 foresight report, launched at the forum, puts the annual agrifood financing gap at $180 billion, while estimating that closing Africa’s yearly $67 billion-$108 billion shortfall in infrastructure finance could halve post-harvest losses and increase farmer incomes by up to 40%.
However, the cost of transitioning to clean energy is still a major barrier for farmers and agribusinesses.
Atinuke Lebile, CEO of Nigerian food processing company Cato Foods, told Climate Home News she would like to switch to using renewables but has been held back by the upfront cost of setting up the systems the firm needs.
Rwandan farmer Gezel also said she would like to invest in a solar irrigation pump, but “it is so expensive”.
Practical Action’s Walender said the challenge is no longer whether solutions exist, but how financial support can reach the communities and businesses where it could have the greatest impact.
“Customers are dispersed and have low incomes. Markets are fragmented, and there are high upfront costs for much energy equipment,” Walender said, adding that financial institutions also often perceive agriculture as a high-risk sector.
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For food processing, the business case for using cleaner energy more efficiently is particularly strong, said Vivian Maduekeh of Partners in Food Solutions, which has worked with more than 2,000 companies across Africa.
Maduekeh said food processing firms account for between 42 and 70% of energy use across food systems, while energy represents 15-22% of their total production costs. African food businesses also use roughly twice as much energy per kilogramme of product as their global competitors, putting them at a competitive disadvantage.
The problems they face in shifting to clean energy are “risk, perception of risk and the cost”, she explained, adding that financial mechanisms are needed to help businesses overcome those issues.
Maduekeh encouraged policymakers to consider measures like tax rebates on imported equipment and spending more on research and development to bring down the cost of productive-use technologies.
Making a range of affordable equipment available – such as smaller irrigation pumps – could also help make the transition more accessible, she said. The evidence in favour “is very clear”, she added. “We just need to package it and communicate it to the priorities of investors.”
The post More support needed to power Africa’s food systems with renewables, experts say appeared first on Climate Home News.
More support needed to power Africa’s food systems with renewables, experts say
Andy Burnham, the UK’s latest prime minister, has suggested reducing the amount the British government gives as climate finance grants and providing some of its climate finance through loans instead, in a move it anticipates will save £400 million.
The government plans to use the savings to fund a cap on bus fares in the UK, triggering accusations from the development sector that Burnham’s proposal “throws Global South countries under the bus”. One likely destination for these new loans is the Tropical Forest Forever Facility (TFFF).
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The TFFF is a new initiative designed to provide payments to countries that protect their rainforests by raising money from governments and private investors, channeling that money into riskier and therefore higher return assets, and using the returns it earns to fund forest protection. But there is a catch.
The UK has committed to provide around £6 billion in climate finance funded through aid (or official development assistance, ODA) over the next three years. If switching from grants to a loan to the TFFF reduces government spending, it will likely reduce the amount that counts as ODA as well.
In other words, the government can make the £400 million saving, or meet its £6 billion aid budget-funded climate finance commitment, but it probably cannot do both. The UK cannot have its cake and eat it.
How will it score as ODA?
Whether any loan to the TFFF scores as ODA depends on the OECD’s Development Assistance Committee (DAC) which is currently deliberating on this topic.
A plain reading of the DAC’s current reporting rules suggests that the TFFF would count as a multilateral organisation: the independent investment arm, the Tropical Forest Investment Fund, would ultimately be a global, official entity (with sovereign governments appointing the board and being sole equity holders), which pools capital from sponsor governments. This would mean that to count as ODA, any loan to it would have to charge less than 5% interest.
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The current concept note suggests a return for sponsor capital equivalent to US borrowing costs of a similar duration: currently around 5.2%, which would make any such loans ineligible. The UK could choose to charge less, but if the UK charges less than it borrows (also above 5%), the difference will add to the deficit in future years. And ODA accounting is not binary: if the UK charges just under 5%, only a small fraction of the loan would count.
At the same time, the risk profile of TFFF is not the same as your average multilateral, and there is speculation that the DAC could allow higher interest loans to TFFF to partially count (by changing the ‘discount rate’ used to measure how concessional the loan is). The TFFF’s own modelling suggests that the risk of the UK losing money on the loan would be fairly limited: roughly a 1% chance of some capital impairment in the riskiest scenario. But some analysts doubt the accuracy of this model and view the risk as much greater.
Would it really save money?
If the risk really is higher, then it might justify counting more ODA on a loan to the TFFF, but it also undermines the arguments that this would create savings for the government. Loans generally don’t count towards the deficit because they create an asset. But that only works if the loan is expected to be fully repaid. If there is a material risk of losing money, then at least some of the transaction will also count towards the deficit.
One possibility is that the loan will be ‘partitioned’ into a financial asset (the part which is expected to be repaid and wouldn’t count towards the deficit) and a ‘capital transfer’ (the part not expected to be repaid). The greater the risk, the larger that second component, and the bigger the impact on the deficit.
This would be the ODA and public accounting rules working as intended. ODA is a measure of ‘donor effort’, usually taken to mean fiscal impact. If it counts as ODA, it should have an impact on the deficit. And the fiscal treatment itself is governed by numerous international accounting standards, a key purpose of which is preventing politically motivated obfuscation of how governments spend their money. If it costs money, there should be an impact on the deficit even if it is a loan. If it doesn’t, it shouldn’t count as ODA (even if there have been exceptions in the past).
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We still know too little about the details to be sure how a loan to the TFFF (or a more exotic transaction) would count towards either ODA or the UK’s headline measures of debt and deficit. The key parameter for each is risk: the lower risk, the more likely it is that the transaction will save money, but the greater the chance that the government would have to spend more ODA elsewhere to meet its climate finance target.
If the UK believes in the TFFF business model and wants to preserve tropical forests, then it should invest. But this decision should not be driven by optimistic accounting tricks. The government cannot expect to reduce the real value of climate finance to partner countries by giving less in grant money, without this having an impact on commitments to spend that money.
The post UK’s budget juggling trick with rainforest loan for bus-fare cap needs transparency appeared first on Climate Home News.
UK’s budget juggling trick with rainforest loan for bus-fare cap needs transparency
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