Extreme global climate outcomes are possible even at 2C of warming

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https://www.ufz.de/index.php?en=36336&webc_pm=14/2026

Press Release, 25. March 2026

Study led by UFZ highlights the need for ambitious climate mitigation measures

Extreme climate impacts on people and the environment are often associated with very high levels of global warming (3 or 4°C). A new study led by the Helmholtz Centre for Environmental Research (UFZ) shows that this assumption is too simplistic. Even moderate warming of 2°C could pose considerable climate risks for sectors that are particularly important for society and ecosystems. These include densely populated regions facing heavy rainfall, key agricultural areas affected by droughts, and forests exposed to extreme fire weather conditions. This underlines the urgency of rapid climate mitigation measures to limit these risks. The study has been published in Nature.

Because climate models still involve considerable uncertainties, it cannot be ruled out that the global climate could develop far more dramatically than expected. “In the interest of responsible risk assessment, we should therefore look beyond the most likely ranges projected by climate models and consider extreme outcomes that could have severe societal or environmental consequences”, says lead author and UFZ climate researcher Dr Emanuele Bevacqua. Until now, these worst-case “extreme global climate outcomes” have typically been described using the average results of many climate models at high levels of global warming (3 or 4°C). However, this approach does not take into account the fact that even at moderate levels of global warming, individual climate projections for certain regions can be very severe. “Furthermore, weather patterns in neighbouring regions tend to be strongly correlated, whereas those in distant regions are largely uncorrelated. This makes it difficult to infer global risks from local uncertainty estimates”, says co-author Prof Dr Jakob Zscheischler, climate researcher at the UFZ and Professor for Data Analytics in Hydro Sciences at TUD Dresden University of Technology.

The researchers therefore adopted a new approach for their study: they identified sector-specific drivers of climate impact such as precipitation extremes and droughts as well as regions where vulnerable sectors (e.g. forests, agriculture, and densely populated areas) are located. Combining these factors makes it possible to examine climate changes in locations where they are particularly relevant for specific global risks. For example, they analysed heavy rainfall in densely populated regions, droughts in major global agricultural regions, and fire-conducive weather in forests. To do this, they evaluated global simulations from many different climate models, which also form the basis of the reports of the Intergovernmental Panel on Climate Change (IPCC). In this way, they were able to identify the model projections that show the strongest (worst-case) and the weakest (best-case) outcomes respectively for each sector examined.

The key finding: for each of the three global domains examined (heavy rainfall in densely populated regions, droughts in global agricultural regions, and fire-conducive weather in forests), some individual climate model projections show considerably greater changes at 2°C of warming than the average across all models at 3°C or even 4°C. This is particularly evident in relation to food security, by focussing on growing regions that account for a large share of global production of maize, wheat, soy, and rice. In this area, the climate models show very large differences. Depending on the model, the frequency of droughts at 2°C of warming may remain unchanged or increase by more than 50%. “At 2°C, 10 of the 42 models examined produce a drought increase that is considerably above the model average at 4°C of warming”, says Bevacqua. The risk of droughts in globally important growing regions is therefore much higher than would be expected from an analysis of model averages. Given their importance for food security, global supply chains, and international markets, the consequences of such extreme climate developments need to be examined more closely. In the domains ‘heavy rainfall in densely populated regions’ and ‘extreme fire weather in forested areas’, the worst-case models at 2°C also show climate trends that exceed the average changes at 3°C of warming.

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Bevacqua, E., Fischer, E., Sillmann, J. et al. Moderate global warming does not rule out extreme global climate outcomes. Nature 651, 946–953 (2026). https://doi.org/10.1038/s41586-026-10237-9

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1. James Hansen et al: Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and...

https://acp.copernicus.org/articles/16/3761/2016/acp-16-3761-2016.pdf

Atmos. Chem. Phys., 16, 3761–3812, 2016
www.atmos-chem-phys.net/16/3761/2016/
doi:10.5194/acp-16-3761-2016
© Author(s) 2016. CC Attribution 3.0 License.

Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 °C global warming could be dangerous

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Received: 11 June 2015 – Published in Atmos. Chem. Phys. Discuss.: 23 July 2015
Revised: 17 February 2016 – Accepted: 18 February 2016 – Published: 22 March 2016

Abstract. We use numerical climate simulations, paleoclimate data, and modern observations to study the effect of growing ice melt from Antarctica and Greenland. Meltwater tends to stabilize the ocean column, inducing amplifying feedbacks that increase subsurface ocean warming and ice shelf melting. Cold meltwater and induced dynamical effects cause ocean surface cooling in the Southern Ocean and North Atlantic, thus increasing Earth’s energy imbalance and heat flux into most of the global ocean’s surface. Southern Ocean surface cooling, while lower latitudes are warming, increases precipitation on the Southern Ocean, increasing ocean stratification, slowing deepwater formation, and increasing ice sheet mass loss. These feedbacks make ice sheets in contact with the ocean vulnerable to accelerating disintegration. We hypothesize that ice mass loss from the most vulnerable ice, sufficient to raise sea level several meters, is better approximated as exponential than by a more linear response. Doubling times of 10, 20 or 40 years yield multi-meter sea level rise in about 50, 100 or 200 years. Recent ice melt doubling times are near the lower end of the 10–40-year range, but the record is too short to confirm the nature of the response. The feedbacks, including subsurface ocean warming, help explain paleoclimate data and point to a dominant Southern Ocean role in controlling atmospheric CO₂, which in turn exercised tight control on global temperature and sea level. The millennial (500–2000-year) timescale of deep-ocean ventilation affects the timescale for natural CO₂, change and thus the timescale for paleo-global climate, ice sheet, and sea level changes, but this paleo-millennial timescale should not be misinterpreted as the timescale for ice sheet response to a rapid, large, human-made climate forcing. These climate feedbacks aid interpretation of events late in the prior interglacial, when sea level rose to +6–9 m with evidence of extreme storms while Earth was less than 1 ◦C warmer than today. Ice melt cooling of the North Atlantic and Southern oceans increases atmospheric temperature gradients, eddy kinetic energy and baroclinicity, thus driving more powerful storms. The modeling, paleoclimate evidence, and ongoing observations together imply that 2 °C global warming above the preindustrial level could be dangerous. Continued high fossil fuel emissions this century are predicted to yield (1) cooling of the Southern Ocean, especially in the Western Hemisphere; (2) slowing of the Southern Ocean overturning circulation, warming of the ice shelves, and growing ice sheet mass loss; (3) slowdown and eventual shutdown of the Atlantic overturning circulation with cooling of the North Atlantic region; (4) increasingly powerful storms; and (5) non-linearly growing sea level rise, reaching several meters over a timescale of 50–150 years. These predictions, especially the cooling in the Southern Ocean and North Atlantic with markedly reduced warming or even cooling in Europe, differ fundamentally from existing climate change assessments. We discuss observations and modeling studies needed to refute or clarify these assertions.

1 Introduction
Humanity is rapidly extracting and burning fossil fuels without full understanding of the consequences. Current assessments place emphasis on practical effects such as increasing extremes of heat waves, droughts, heavy rainfall, floods, and encroaching seas (IPCC, 2014; USNCA, 2014). These assessments and our recent study (Hansen et al., 2013a) conclude that there is an urgency to slow carbon dioxide (CO₂ ) emissions, because the longevity of the carbon in the climate system (Archer, 2005) and persistence of the induced warming (Solomon et al., 2010) may lock in unavoidable, highly undesirable consequences.

Despite these warnings, fossil fuels remain the world’s primary energy source and global CO₂ emissions continue at a high level, perhaps with an expectation that humanity can adapt to climate change and find ways to minimize effects via advanced technologies. We suggest that this viewpoint fails to appreciate the nature of the threat posed by ice sheet instability and sea level rise. If the ocean continues to accumulate heat and increase melting of marine-terminating ice shelves of Antarctica and Greenland, a point will be reached at which it is impossible to avoid large-scale ice sheet disintegration with sea level rise of at least several meters. The economic and social cost of losing functionality of all coastal cities is practically incalculable. We suggest that a strategy relying on adaptation to such consequences will be unacceptable to most of humanity, so it is important to understand this threat as soon as possible.

We investigate the climate threat using a combination of atmosphere–ocean modeling, information from paleoclimate data, and observations of ongoing climate change. Each of these has limitations: modeling is an imperfect representation of the climate system, paleo-data consist mainly of proxy climate information usually with substantial ambiguities, and modern observations are limited in scope and accuracy. However, with the help of a large body of research by the scientific community, it is possible to draw meaningful conclusions.

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