资源环境科技发展态势分析平台

By analyzing observations and model simulations, here we show that there exists a significant anticorrelation on interannual to multidecadal time scales between the Sahel and southeast Amazon rainfall during July-August-September. This rainfall seesaw, which is strongest on decadal to multidecadal scales, is due to an anomalous meridional gradient of sea surface temperatures across the tropical Atlantic that pushes the Intertropical Convergence Zone and its associated rain belt toward the anomalously warm hemisphere. Large ensemble model simulations suggest that the seesaw pattern is likely caused by decadal changes in anthropogenic and volcanic aerosols, rather than internal climate variability. Our results suggest that the recent decadal to multidecadal climate variations in and around the North Atlantic basin are largely externally forced and that projected large North Atlantic warming could lead to a wetter Sahel but drier Amazon in the future.

Plain Language Summary Both the semiarid Sahel and Amazon rain forest are known hot spot regions of climate change. However, the causes of Sahelian and Amazonian rainfall variations are still debated and the scientific community has often examined these two regions separately rather than collectively. Here we show that there exists a significant decadal rainfall seesaw pattern between the Sahel and southeast Amazon during July-August-September in observations and coupled model simulations. This seesaw pattern is likely caused externally by decadal changes in anthropogenic and volcanic aerosols, rather than internal climate variability. Our findings not only detect and attribute the seesaw pattern over the Sahel and Amazon Basin but also provide further evidence for major impacts of external forcing on recent decadal climate variations in and around the North Atlantic Ocean.