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Human-induced greenhouse gas emissions are amplifying climate change and its impacts – this is agreed on by the scientific community. One consequence is that extreme events like heat and droughts are becoming more frequent and more intense. A new study in the journal Geophysical Research Letters by researchers of the Alfred Wegener Institute shows that human greenhouse gas emissions are also the dominant driver of events that combine hot and dry extremes. It also emphasizes climate inequalities: low-income countries face disproportionately high risks despite contributing relatively little to global emissions.
The Earth's energy balance is becoming increasingly unbalanced - according to the latest report from the World Meteorological Organisation (WMO). The resulting climate changes are leading to more frequent and more extreme events such as heatwaves and droughts. “These two extremes already cause enormous damages on their own, such as reduced productivity in agriculture and industry, acute water shortages and increased mortality among humans and livestock”, says Di Cai, first author of the study from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI). “Combined, hot-dry extremes generate outcomes that exceed or differ significantly from the cumulative effects of individual events.”
In their study, the AWI-researchers assessed the development, drivers and impacts for humans of compound hot-dry extremes. They analyzed 152 simulations from eight CMIP6 climate models together with observational and socioeconomic datasets. One part of the analysis compared changes in temperature, precipitation, and the frequency and duration of hot-dry events between a pre-industrial baseline (1850 to 1900), the present day (2001 to 2020), and a future climate under about 2.7 °C of global warming. Additional analyses were used to identify the role of greenhouse gas emissions and to estimate how population exposure changes under different warming and population scenarios.
“Beyond documenting the physical changes, we also analyzed how strongly populations are affected by hot-dry events under different warming targets”, says Dr. Monica Ionita, co-author and an expert on weather forecasting at AWI. “The goal was to understand not only how these compound extremes intensify, but also who will be most affected and how much stronger climate policies could reduce future exposure.”
Human greenhouse gas emissions drive hot-dry events, leading to climate inequality
The simulations show that the dominant driver behind the increase in compound hot-dry events is the rising global temperature, amplified by land-atmosphere feedbacks. These changes are driven primarily by human greenhouse gas emissions rather than by natural variability. The AWI-team also found a linear relationship between global temperature rise and the fraction of the population exposed to heightened compound hot-dry extremes. “If current climate policies stay the same, nearly one third of the global population could face more frequent and severe hot-dry conditions by the end of the century”, says Di Cai. That would be nearly 2.6 billion people. To put this into perspective: based on current global average per-capita emissions, the lifetime carbon emissions of about 3.4 people would be enough to expose one additional person to heightened compound hot-dry extremes by the end of the century.
This vulnerability comes largely from geographic location and the inherent climate sensitivity of those regions. The most affected nations are predominantly situated in tropical and subtropical latitudes, where even modest warming can trigger significant shifts in extreme event likelihood. Another link that the paper shows is that low-income countries face disproportionately high risks of these extreme conditions, even though they are contributing relatively little to global emissions, as limited adaptive capacity and resources may further exacerbate these risks. Primary hotspots are Central and South America, southern Europe, Africa, and southern Asia.
“Our study shows the urgent need for fair and immediate climate action that protects those most at risk”, says Di Cai. “By combining physical climate attribution with population exposure and national inequality, we provide evidence that is directly relevant for climate-risk assessment across regions, adaptation planning, and international climate-justice debates.” Monica Ionita adds: “Countries that are least responsible for emissions may bear some of the greatest risks, which strengthens the need for more ambitious mitigation, targeted adaptation support, and international climate-finance mechanisms. The results also show that exposure rises sharply beyond 1.5 °C, highlighting the benefits of stronger mitigation and lower-warming pathways.”
Di Cai
+49 (0)471 4831-1760
di.cai@awi.de
Cai, D., Lohmann, G., Chen, X., & Ionita, M. (2026). Compound hot-dry extremes amplify disproportionate climate risks for low-income nations. Geophysical Research Letters, 53, e2025GL118822. https://doi.org/10.1029/2025GL118822
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Drought in central Germany
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Drought in central Germany
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