Abstract

There are a slew of ways atmospheric circulation responds to increased CO2 . In the troposphere, the Hadley Circulation expands, the tropical upwelling narrows, and the subtropical jet strengthens. Meanwhile in the stratosphere, the Brewer-Dobson Circulation accelerates, seen by the narrowing and strengthening of the tropical upwelling. Although recent work revealed independent circulation changes between the two domains, no study has successfully isolated the response of the upper troposphere from that of the lower stratosphere. Here, we present a deeper examination of the patterns related to the circulation responses in the upper troposphere and lower stratosphere. First, we design idealized simulations with the NASA Goddard Institute for Space Studies (GISS) E2.2 model to decompose the full atmospheric response to CO2 into three components; the direct CO2 radiative response, the response to sea surface temperature changes, and the response to the interactive ozone. This decomposition shows how the ozone impact on the BDC strength is as large as the direct CO2 radiative response and isolates the lower stratospheric circulation response with negligible change in the troposphere. Second, we present a comprehensive view of the Hadley Circulation’s response to CO2 forcings ranging from 2- to 8xCO2. Analysis of output from the  NASA GISS E2 .2 model shows the upper tropospheric circulation response is also decoupled from that of the lower troposphere; lower tropospheric features show curious nonlinearity between 2- and 4xCO2, the response of the upper troposphere largely reflects a vertical shift in the circulation, and the regional patterns of circulation response deviate from conclusions derived by the zonal-mean framework. Altogether, these findings offer new insight into the physical processes involved in the distinct upper tropospheric and lower stratospheric responses to increased CO2 .