Joint Seminar: The recent weakening of the summertime circulation: What is the role of Arctic Sea ice loss?
Reanalysis data show summertime storminess in the Northern Hemisphere midlatitudes has weakened significantly with important implications for weather and air quality. Previous literature and the news media often suggest a role for Arctic Sea ice loss but its impact has not been examined quantitatively. Here we quantify the impact of summertime Arctic Sea ice loss on the Northern Hemisphere circulation. We use climate model simulations with constrained Arctic Sea ice to show present-day Arctic Sea ice loss does not significantly affect the recent circulation weakening even though it is projected to have an impact in the late 21st century. The results suggest that anthropogenic forcing without Arctic Sea ice loss is responsible for the weakening summertime circulation. Accordingly, we quantify the impact of anthropogenic forcing on the summertime circulation weakening using Detection and Attribution Model Intercomparison Project simulations. The results show that anthropogenic aerosols and greenhouse gases contribute equally but their impact varies regionally. Anthropogenic aerosols dominate the weakening in the Pacific sector while greenhouse gases dominate in the Atlantic sector. We quantitatively connect the aerosol-induced changes in temperature and shortwave radiation to circulation changes. Our results show aerosol and greenhouse gases are the dominant contributors to recent Northern Hemisphere summertime regional climate change.
- Bundesstr. 53, room 022/023
- Seminar Room 022/023, Ground Floor, Bundesstrasse 53, 20146 Hamburg, Hamburg
- Zoé Rehder