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Abstract
The atmospheric circulation exhibits robust responses to increased CO2 that emerge across the climate model hierarchy. Existing theoretical explanations of the circulation response can be grouped according to latitude. Here we test latitudinally dependent explanations of the circulation response to increased CO2 using slab ocean aquaplanet models with latitudinally dependent CO2 concentration. Quadrupling CO2 in the tropics (0–20°) accounts for the strengthening and upward shift of the subtropical jet but does not account for the poleward shift of the Hadley cell edge or extratropical circulation. The tropical response is dominated by regions of descent. When CO2 is quadrupled in high latitudes (60–90°), there is a negligible circulation response. The response to latitudinally dependent increased CO2 is mostly linear and increased CO2 in the midlatitudes (20–60°) dominates. Within the midlatitudes, the subtropics (20–40°) dominate. Thus, story lines explaining the circulation shift in response to increased CO2 should focus on the thermodynamic response in the subtropics.