image: a, Spatial distribution of the summer SAT (°C) difference between high- and low-emission scenarios (SSP5-8.5 and SSP1-2.6, respectively) for 2060‒2099. Vertical colored strips represent the temporal evolution of summer SAT (°C) difference between high- and low-emission scenarios over central North America (NA: 36°‒53°N, 92°‒115°W), mid-latitudes of western and central Eurasia (EUR: most of Europe and western Siberia, covering [36°‒49°N, 8°W‒30°E], [36°‒55°N, 30°‒48°E], and [48°‒55°N, 48°‒86°E]), and other regions of the world (Other) for 2015‒2099. b,c, Same as a, but for extreme high-temperature and aridity index, respectively. Red, blue, and black bars show the latitude-weighted regional averages of SAT, extreme high-temperature, and aridity index over NA, EUR, and Other for 2060‒2099. Black lines delineate the regions of NA and EUR. Areas are marked with stippling where the GHG-driven changes (SSP5-8.5 minus SSP1-2.6) are deemed robust: specifically, where at least 80% of the models project a local change greater than the global land average.
Credit: ©Science China Press
Intensified GHG Emissions Drive Extreme Dry-Hot Extremes in North America and Europe
Although GHG are distributed relatively uniformly worldwide, the warming and climate effects they trigger exhibit significant regional differences. This phenomenon is closely linked to local climate backgrounds and feedback processes activated by rising temperatures. Our study clearly reveals that if GHG emissions remain uncontrolled, North America and Europe will experience warming amplitudes of 3.7°C ± 0.7°C and 3.8°C ± 0.5°C, respectively, by the end of the 21st century—significantly higher than the global average warming level of 2.7°C ± 0.4°C. Concurrently, the extent of drought in these two regions is projected to expand by 45.9% ± 11.9% and 13.4% ± 6.7%, respectively, highlighting the regional concentration and severity of extreme dry-hot trends.
Land–Air “Dry-Hot” Feedback as a Key Mechanism for Extreme Dry-Hot Conditions in North America and Europe
GHG forcing and local land–air “dry–hot” feedback are the primary drivers of the nonlinear intensification of drought and warming in North America and Europe. The study shows that enhanced land–air coupling, triggered by GHG forcing, contributes 23.0±9.8% and 22.4±10.5% of the total warming in North America and Europe, respectively—significantly higher than in other regions (7.9±4.5%). At the same time, land–air coupling expands the extent of drought-prone areas in North America and Europe by 44.2±18.7% and 22.6±12.6%, respectively, while this effect is nearly negligible in other regions (1.6±2.1%). The study further indicates that if the contribution of land–air coupling were excluded from GHG forcing, North America and Europe would no longer stand out as notable hotspots of warming and aridification. More importantly, the extreme dry–hot climate induced by land–air coupling is projected to significantly suppress Gross Primary Productivity (GPP): GPP in North America and Europe is expected to decrease by 27.1±20.1 and 28.8±16.9 g C·m⁻²·month⁻¹, respectively, whereas other regions remain largely unaffected. This impact would partially offset the positive effect of CO₂ fertilization on vegetation growth, weaken the ecosystem’s responsiveness to increasing GHG, and thereby heighten the risk of regional ecological degradation.
Physical Mechanism Behind the "Dry-Hot" Feedback
The physical mechanism through which intensified land–air coupling leads to extreme dry–hot conditions in North America and Europe can be summarized as follows: under global warming, persistent decline in soil moisture in these regions reduces actual evapotranspiration. This reduces cloud cover, thereby increasing the shortwave radiation reaching the land surface. At the same time, weakened evapotranspiration significantly alters the distribution of surface energy fluxes—latent heat flux decreases while sensible heat flux increases. Overall, the land surface receives more net energy, and a greater proportion of this energy is transferred to the atmosphere as sensible heat. These two effects jointly enhance the land surface's capacity to heat the lower atmosphere, which not only raises surface air temperatures directly but also increases potential evapotranspiration, further aggravating soil aridity and thereby sustaining a positive "dry–hot" feedback loop.
Outlook
The findings of this study indicate that if uncontrolled GHG emissions continue, the triggered "dry-hot" feedback will make North America and Europe the most prominent regions globally in terms of dry-hot amplification and expose them to the most severe climate risks. In fact, these regions are already frequently experiencing more intense heatwaves and flash droughts. In contrast, if stringent GHG mitigation is implemented worldwide, the warming and drying trends in these areas would be significantly alleviated, thereby delivering the greatest climate benefits. Therefore, countries in North America and Europe should be strongly motivated not only to actively advance their own emission reduction efforts but also to assist other nations in implementing climate actions, accelerating global achievement of carbon peak and carbon neutrality goals.
Highlights
This study is the first to clearly indicate that under an uncontrolled high-emissions scenario, GHG forcing would make North America and Europe the regions with the highest risk of extreme dry-hot events worldwide. It confirms that intensified land–air coupling is the key physical mechanism responsible for the anomalous warming and aridification in these regions, and it quantitatively assesses the magnitude of this contribution. These findings underscore the indispensable role of GHG mitigation in alleviating extreme climate disasters triggered by land–air coupling.
The research team, led by academician Zhang Renhe's team from Fudan University, the corresponding authors are Professor Zhiyan Zuo and Academician Renhe Zhang from the Department of Atmospheric and Oceanic Sciences at Fudan University, Associate Professor Liang Qiao from the College of Atmospheric Sciences at Lanzhou University is the first author. The co-authors include Professor Wei Mei (Department of Atmospheric and Oceanic Sciences, Fudan University), Professor Deliang Chen (Foreign Member of the Chinese Academy of Sciences, Department of Earth System Science, Tsinghua University), Ph.D. student Meiyu Chang, and postdoctoral researcher Kaiwen Zhang (both from the Department of Atmospheric and Oceanic Sciences, Fudan University).