PAOC Colloquium (PAOCQ) – Rei Chemke (Weizmann Institute)

“Human influence on the large-scale atmospheric flow in recent decades”

Abstract:
The large-scale atmospheric flow plays a central role in shaping the regional weather and climate on Earth. On daily to multi-decadal timescales, the tropical and extra-tropical flows are responsible for the transport of heat, momentum and moisture across latitudes and longitudes, thereby affecting the distribution of precipitation, temperature and winds. It is thus critical to assess the impacts of anthropogenic emissions on the large-scale flow. Yet, while observed thermodynamic changes have been attributed to human emissions with high confidence, currently these is a large uncertainty in recent circulation changes. This uncertainty precludes both assessing the impacts of human emissions on the circulation, and, informing our confidence in climate projections. Here I will present two examples of how the large-scale flow have changed in recent decades, and assess the relative role of anthropogenic emissions in these changes. Specifically, first, I will show that climate models severely underestimate the recent intensification of winter storm tracks in the Southern Hemisphere, which questions their ability to accurately predict climate changes in austral extra-tropics. Second, I will elucidate the models-reanalyses discrepancy in recent changes in the Northern Hemisphere Hadley cell strength. Changes in the Hadley cell strength are constrained by observations of sea-level pressure, and show that the Hadley cell has weakened in recent decades, in agreement with climate models. The weakening of the circulation is further attributed to anthropogenic emissions, which increases our confidence in future human-induced tropical climate changes.

About this series: The PAOC Colloquium is a weekly interdisciplinary seminar series that brings together the whole PAOC community. Seminar topics include all research concerning the physics, chemistry, and biology of the atmospheres, oceans and climate, but also talks about e.g. societal impacts of climatic processes. The seminars take place on Monday from 12-1pm. Contact paoc-colloquium-comm@mit.edu for more information and Zoom password.