Limiting warming to 2C above pre-industrial temperatures may not be enough to prevent “extreme global climate outcomes”, according to research published in Nature.
The authors simulate climate extremes – such as drought in breadbasket regions and flooding in populated areas – under a 2C warming scenario using a range of different global climate models.
They find that the “worst-case” model projections in a 2C warmer world are often more severe than the “average” scenarios in a 3C or 4C warmer world.
An author on the study tells Carbon Brief that, for policymakers planning around risk, it is “really important” to account for these potential extremes at 2C.
The findings are “sobering” and “demonstrate that the risks at 2C of global warming may be significantly higher than previously thought”, according to one scientist who was not involved in the study.
He adds that the methods used in the research would “offer a very useful contribution” to any future “global assessment of avoidable climate-change risks”.
High-risk scenarios
As the planet warms, climate extremes such as floods and droughts are becoming more intense and frequent. For policymakers to effectively plan and adapt to upcoming changes, they need to understand how severe these events could become.
Scientists routinely use global climate models to simulate how extremes may change over the coming decades. One well-established way to present these results is to run simulations using multiple models, then take the average of these results.
This average is known as the “multimodel mean”. Model results typically cluster around the mean, giving scientists more confidence in these results, but there are often also individual projections that sit notably higher or lower.
Prof Erich Fischer is a lecturer in environmental systems science at ETH Zurich and an author on the paper. He tells Carbon Brief that focusing on the multimodel mean is a “very valuable” communication tool for climate scientists, providing a “simpler” message than showing the full range of results.
For example, he tells Carbon Brief that the Intergovernmental Panel on Climate Change (IPCC) – the world’s most authoritative source on climate change – uses the multimodel mean to produce many of its maps.
However, Fischer warns that from a “risk perspective”, focusing solely on the multimodel mean could give a “misleading picture”. For example, he adds, the changes that specific regions may see could be “much, much higher” than the global average.
He tells Carbon Brief that for policymakers planning around risk, it is “really important” to account for more extreme cases too.
To demonstrate this, the study authors select 42 models from the Coupled Model Intercomparison Project 6 (CMIP6). These are the models that are used most widely in the latest set of IPCC reports.
Their approach is illustrated in the diagram below. Note that this illustration is not based on real model runs, but is intended to give an example of what a set of results could look like.
The beige strip on the right shows the spread of results, where each horizontal bar indicates a different model. The models simulating the “worst-case” outcomes (red lines) are at the top and those showing the “best-case” climate outcomes (blue lines) are at the bottom. The majority of models are clustered towards the centre of the bar, close to the multimodel mean (thick black line).
The authors selected three types of events to analyse:
- Rainfall extremes in highly populated areas, which may induce flooding
- Concurrent droughts in global breadbaskets, which threaten food security
- Fire weather extremes across the world’s forests
For each event type, the authors assess the spread of results. They rank the model outputs by the severity of each type of event and compare these to the multimodel mean at different levels of warming – including 2C, 3C and 4C above pre-industrial temperatures.
In many instances, the “worst-case climate outcomes” in a 2C world are more severe than the multimodel mean in a 3C or 4C world.
Prof Rowan Sutton, director of the Met Office Hadley Centre, who was not involved in the study, tells Carbon Brief that the study’s findings are “sobering”. He adds that the paper “demonstrates that the risks at 2C of global warming may be significantly higher than previously thought”.
In its latest assessment report, the IPCC projected that, under current policies, the world could reach 2C of warming between 2037 and 2084, with a central estimate of 2052. (For more on when the IPCC says warming thresholds will be passed, read Carbon Brief’s explainer.)
Breadbasket drought
The analysis of drought in key breadbasket regions provided the “most striking results”, Dr Emanuele Bevacqua, a researcher at the Helmholtz Centre for Environmental Research and lead author of the study, tells Carbon Brief.
To assess the worst-case scenario, the authors simulated drought frequency in “critical breadbasket areas across the world”, he explains.
These are the regions where most of the world’s maize, wheat, soybean and rice is grown, including regions of northern and southern America, Europe, south-eastern Asia and Australia.
The spread of model results is shown below.
The vertical bars indicate the percentage change in average drought frequency between a pre-industrial and 2C warmer world, where more-frequent drought is at the top of the bar and less-frequent drought is at the bottom.
On the left bar, each horizontal line indicates one model. The models showing the “worst-case climate outcomes” are highlighted at the top of the bar. On the right bar, the horizontal bars show the multimodel means for warming levels of 2C, 2.5C, 3C and 4C.
The percentage change in drought frequency in key breadbasket regions between a pre-industrial and 2C warmer world. On the beige bar (left), each horizontal line indicates a model. On the grey bar (right), the horizontal bars show the multimodel means for warming levels of 2C, 2.5C, 3C and 4C. Source: Bevacqua et al. (2026)
They find that 10 of the 42 models simulate a level of drought frequency at a 2C warming level that is higher than the multimodel mean at 4C warming.
(Some models also project a lower level of drought frequency at 2C warming than the multimodel mean. However, the focus of the study is to capture the most severe risks, which are particularly relevant for risk management.)
Bevacqua tells Carbon Brief that this result “makes it very clear that even if we stop [warming] at 2C, we cannot rule out the fact that we might end up in a worst-case outcome”.
The authors also conduct their analysis for extreme rainfall in populated regions. Although they find a wide range of model results, none of the simulations of extreme rainfall at 2C are higher than the multimodal mean at 4C.
Meanwhile, analysing the risk of wildfires to the world’s forests reveals that four of the models simulate more severe fire risk at 2C than the multimodel mean at 3C and none simulate more severe fire risk at 2C than at 4C.
The spread of model results for rainfall (left) and wildfire (right) are shown below.
Dr Karen McKinnon is an associate professor in statistics and the environment at the University of California, Los Angeles. McKinnon, who was not involved in the study, tells Carbon Brief that the study highlights that “risks are obscured when considering averages across multiple climate models”.
‘Worst-case scenarios’
The authors find that the ranking of models was different across the three case studies. In other words, the same models did not produce the “worst-case” climate outcomes in every type of event.
When assessing the impact of future extremes, the findings emphasise the need to select models that “sample the full range of possible climate outcomes”, the paper says. It adds:
“Currently, large-scale initiatives such as the latest protocol of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP) rely on a limited subset of climate models that likely omits the best- and worst-case climate models.”
ISIMIP is a global modelling effort to project the impacts of climate change across different sectors. Bevacqua notes:
“[O]ur results suggest that ISIMIP-based simulations probably underestimate the range of possible global impacts at a fixed global warming level of +2C.”
He adds:
“This is worrying and calls for new approaches that can somehow lead to accounting for this.”
The study also shows that many “best-case” model outcomes for a 2C world project a lower level of risk than the multimodel mean. However, Fischer notes that “even the best-case scenario” shows that extremes will become more severe with warming.
Fischer says that the study authors are not “doomscrolling” and notes that “landing somewhere in the middle is still the more likely outcome”. However, he emphasises the importance of considering the high-impact model outcomes for planning around risk.
Communicating risk
Climate scientists and policymakers have been discussing how best to assess and communicate climate risk for decades.
Dr Robert Vautard – senior climate scientist at France’s National Centre for Scientific Research at Institut Pierre-Simon Laplac, who was not involved in the study – tells Carbon Brief that the study provides “very insightful examples of outcomes for communicating risks”.
However, he questions whether the “global indices” used in this study would be relevant for developing “regional” adaptation plans, noting that worst-case impacts in the model “may not be the most problematic locally”.
Last month, a group of leading climate scientists published a comment article – also in Nature – calling for a global climate risk assessment that identifies the “worst-case scenarios” and helps societies to prepare for them.
The article says:
“Global assessments made by IPCC have played, and continue to play, a crucial part in assessing the evidence about climate change. But the IPCC produces science assessments, rather than risk assessments. Its main focus has been to set out what is known with the greatest confidence.
“A climate risk assessment offers different information – it makes clear the scale and severity of risks, to inform judgments about the priority to be given to avoiding or mitigating them.”
Sutton, the Hadley Centre director, is an author on the article. He tells Carbon Brief that “from a policy and decision-making perspective, climate change is a problem of risk assessment and risk management”.
He says that the methods used in this study “offer a very useful contribution to a global assessment of avoidable climate-change risks”.
The post Limiting global warming to 2C would not ‘rule out’ extreme impacts appeared first on Carbon Brief.
Limiting global warming to 2C would not ‘rule out’ extreme impacts
A new study calculates the dollar value of wetlands in reducing river flooding. But in Sackett vs. EPA, the high court rolled back protections for nature’s first line of defense.
The destruction of wetlands in the United States has increased the amount of flood insurance claims by $10 billion over the past 40 years, a phenomenon expected to worsen in tandem with climate change, according to new research.
Supreme Court’s Limitation on Wetlands Protection Will Make Flooding Worse
In a school in South Africa, a group of students stare at a row of small plants growing in a greenhouse. Each one is involved in the lesson, caring for the growing crops.
But this is no ordinary classroom setting. These children are learning about aquaponics, a method of growing plants and fish in a mutually beneficial water system. This ancient technique of food production is now being taught to millions of schoolchildren after being introduced by the South African government seven years ago.
Laerskool Kempton Park on the edge of Johannesburg was one of the first schools to introduce the subject with the aim of improving food security. This is a serious challenge in a country where an estimated 19.7 million people, or around 30% of the population, experience moderate levels of food insecurity, meaning that they struggle to afford enough food for a healthy, balanced diet.
Bringing the farm to school
Aquaponics is a way of supporting communities to access food in a sustainable and efficient way. The solution is simple: fish waste is turned into available nutrients by bacteria in the water. Plants absorb these nutrients and the cleaned water is returned to the fish tank.
There are multiple benefits to this approach. The system doesn’t require chemical fertilisers, soil or large tracts of land. It is also highly efficient, with recirculated water being used over and over again. This is an important feature in areas of South Africa that experience drought or unpredictable weather.
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Aquaponics can offer a range of benefits depending on the local context. In South Africa, townships in major cities such as Johannesburg don’t always have the space to produce their own food, while in other places, such as the Northern Cape, extreme weather is making agriculture much harder.
At Laerskool Kempton Park, the students have benefited from the innovative work of INMED, a non-profit organisation that supports vulnerable children and families in the country.
INMED has trained hundreds of teachers and over 7,000 children on the benefits of aquaponics. With the help of funding from the Adaptation Fund through the UNDP-Adaptation Fund Climate Innovation Accelerator (AFCIA), the organisation was able to develop its own aquaponics system to be used in schools.
Scaling up the solution
INMED describes its prototype as a ‘plug and play’ system, designed to be modular and easy to install and manage. The system includes a 2,000-litre fish tank powered by a solar pump to circulate water. The design is simple with a view that it could be easily replicated across different school settings.
Unathi Sihlahla, director at INMED South Africa, told Climate Home News that “aquaponics speaks to a number of challenges… including limited access to nutritious food, high youth unemployment, water scarcity, and in many cases, poor or no access to arable land.”
INMED’s prototype allows communities to work around these problems as it doesn’t need soil and uses far less water than conventional agriculture.
“We’ve seen schools that previously had no food production now able to grow vegetables consistently, while also producing fish. That food often goes straight into school meals or supports vulnerable households nearby,” Sihlahla added. The project estimates that over 5,300 kilogrammes of food have been harvested in each quarter the system has been operating.
As aquaponics is now part of the school curriculum, many educational departments across South Africa have been looking at ways to teach the subject. INMED’s innovative design could provide a handy solution. The organisation has already started to roll it out across different provinces and a new collaboration with the Eastern Cape Provincial Department of Education is in the works. INMED is also scaling the ‘plug and play’ model in Tanzania.
Giving youth a sense of pride
For educators, teaching schoolchildren new agricultural skills is not only about improving food security, but also about creating the next generation of farmers. This group will need to grow food with the increased threat of extreme weather events and having knowledge of alternative methods, such as aquaponics, could be key.
“Agriculture is not seen as something young people want to go into, but when they are exposed to something like aquaponics, it feels modern and relevant,” said Sihlahla, adding that some students have started their own projects at home or are looking to continue studying the method.
“There’s also a sense of pride. Producing food that supports your school or community changes how young people see themselves and their role.”
Engaging the next generation
The Adaptation Fund’s support for young people extends beyond South Africa. Several other related projects aim to equip youth with practical skills for climate adaptation.
In Costa Rica, a $10-million project implemented by private foundation Fundecooperación included several creative youth-focused programmes in climate-vulnerable areas. It trained young people in coral reef restoration and farming techniques, involved high school students in community water resource monitoring and management, shared knowledge on adaptation through a theatre tour in schools, and created an art mural competition using AI.
Extreme heat is rewriting food security. The best fixes are already within reach
In Lesotho, meanwhile, climate education is being integrated into the school curriculum through climate-smart agriculture materials and teacher training rolled out across primary and secondary schools. This is equipping students from an early age with practical, locally relevant knowledge to build resilience.
“Children and young people are among the most vulnerable to climate change,” said Mikko Ollikainen, head of the Adaptation Fund. “These programmes are not only training young people in adaptation but empowering them.”
Adam Wentworth is a freelance writer based in Brighton, UK.
The post Young South Africans take up sustainable agriculture for food security appeared first on Climate Home News.
Young South Africans take up sustainable agriculture for food security
Just as Colombia – a coal-producing country that has halted new exploration licenses for hydrocarbons – was set to host the first fossil fuel phase-out summit in late April, the government received notice from a foreign energy firm operating on its soil. It was being sued for millions of dollars.
One day before Colombia hosted representatives from around 60 countries for the first Global Conference on Transitioning Away from Fossil Fuels, Spain-based firm Termocandelaria Power, which operates two of the country’s diesel- and gas-fired power plants, sued the government for $198 million alleging a breach of investor protection rules under a bilateral agreement.
Termocandelaria said government measures since 2024 have prevented its Colombian subsidiaries from receiving full payment for the power they supplied to a public utility, while the Colombian government justified its actions as needed to guarantee financial solvency and deliver electricity to rural communities.
While Termocandelaria declined to comment for this article, the company said in a press release last month that investment protection treaties “are designed to provide a stable and predictable legal framework for long-term investments in strategic sectors”.
The timing shows how trade agreements that offer investors protection when government decisions are seen as causing harm to their business – a system known as investor-state dispute settlement (ISDS) – can hamper the transition away from fossil fuels even when countries are pushing for it. Governments in the Global South are particularly exposed, experts told Climate Home News.
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As part of the official academic contribution to the Santa Marta conference, researchers recommended that governments should “recognise” ISDS as a barrier to the energy transition, and called for negotiations on an international initiative to dismantle ISDS protection for fossil fuel investments, either through “a new standalone” international agreement or as part of a broader treaty.
Mario Osorio, a research fellow at the Center for Economic and Policy Research (CEPR), said Termocandelaria’s claim against Colombia “puts in perspective how serious, concrete and real these threats are” for developing countries.
Osorio said the second fossil fuel transition conference – to be held next year in Tuvalu – presents an opportunity for advancing ISDS reform from discussion to “something more concrete”.
Colombia pledges to exit ISDS
ISDS is a mechanism in international trade that allows foreign corporations – many of them linked to fossil fuel interests – to sue governments in international arbitration courts. One 2022 study estimated that possible legal claims from fossil fuel investors could reach $340 billion.
In the lead-up to the Santa Marta conference, Colombian President Gustavo Petro pledged to exit the ISDS system by reviewing Colombia’s 129 investment protection agreements. This came after more than 200 economists sent Petro an open letter urging Colombia to abandon the ISDS system.
Eunjung Lee, a senior policy advisor at UK-based think-tank E3G, said the Santa Marta conference had helped elevate ISDS reform as a key element of the transition away from fossil fuels, despite the issue remaining relatively little-known, even among climate negotiators.
She added that governments tend to be cautious about discussing ISDS at climate summits, as these treaties also implicate trade and economy ministries. “If it is not your file, then you can’t really say much about it and taking action is not necessarily up to you,” she explained.
Kyla Tienhaara, Canada Research Chair in Economy and Environment and a professor at Queen’s University who has worked on the issue for two decades, said the conference in Santa Marta marked a new approach, and that Colombia had placed ISDS “prominently in the agenda”.
The next transition conference presents an opportunity for governments to land on something more practical, particularly under the agreed work stream on “macroeconomic dependence and financial architecture”, but it will depend on the co-chairs Tuvalu and Ireland, she said.
Ireland was sued in May by oil company Lansdowne for failing to award a lease in the Barryroe offshore field. The claim was made under the Energy Charter Treaty (ECT), which fossil fuel companies have used to sue several governments over the consequences of enacting their climate policies.
Following a similar move by some other European states, Ireland left the ECT in April while the Santa Marta conference was ongoing, but existing fossil fuel investments are still protected for 20 years under a “sunset clause”.
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“Disappointing” conference report
Despite the prominence of the issue in the conference rooms, experts told Climate Home that the chairs’ takeaways report was “disappointing”, as it did not explicitly mention ISDS as a key obstacle to the energy transition.
The Netherlands, which co-hosted the summit, may have faced conflicting interests, said Tienhaara, as it is second only to the US as a “home state” for the investors bringing the most ISDS cases, including foreign companies structuring their investments through the country.
The Dutch government also withdrew from the ECT last year, which means it understands and has acted on the threat of investment treaties to climate action, the researcher said. “Unfortunately, they seem unwilling to extend their concern to the harm that these treaties cause in other countries, particularly in the Global South,” she added.
Lee of E3G said Global North countries like the Netherlands tend to export capital to developing countries, which is why they seek to protect their investors’ interests and are unlikely to drive a dismantling of the ISDS system themselves.
Developing countries like Colombia, which have been negatively affected by ISDS claims, have an incentive in “voicing their concerns” and forming a bloc around this topic. “Uniting Global South countries can make a stronger case,” Lee said.
The post Santa Marta process can confront trade protection for fossil fuels, experts say appeared first on Climate Home News.
Santa Marta process can confront trade protection for fossil fuels, experts say
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