资源环境科技发展态势分析平台

The Pacific North American (PNA) pattern is an internal mode of the Northern Hemisphere atmosphere, which strongly affects the hydroclimate and ecosystems of the Pacific-North American sector. Recent studies have suggested a more positive PNA pattern in response to greenhouse warming, but how extreme PNA events will change remains unclear. Based on results from the Coupled Model Intercomparison Project Phase 5 multimodel ensemble, we find a 50% increase in the frequency of extreme positive PNA events and a 32% increase in extreme negative PNA events in the 21st century relative to the twentieth century. The increased frequency arises from a shift toward a more positive PNA pattern and is enhanced by more frequent ENSO events under greenhouse warming. Our study suggests that a continued increase in greenhouse-gas emissions is likely to cause increased occurrence of extreme PNA events, thus increasing the risk of extreme weather and climate in North America.