The Brewer–Dobson circulation in CMIP6

Abstract. The Brewer–Dobson circulation (BDC) is a key feature of the stratosphere that models need to accurately represent in order simulate surface climate variability and change adequately. For first time, Climate Model Intercomparison Project includes its phase 6 (CMIP6) set diagnostics allow for careful evaluation BDC. Here, BDC evaluated against observations reanalyses using historical simulations. CMIP6 results confirm well-known inconsistency sign trends between middle upper stratosphere. Nevertheless, large uncertainty observational trend estimates opens door compatibility. In particular, when accounting limited sampling observations, model error bars overlap 40 % simulations with available output. increasing CO2 an acceleration but reveal spread middle-to-upper stratospheric trends, possibly related parameterized gravity wave forcing. very close connection shallow branch residual temperature highlighted, which absent deep branch. mean age air are shown be more robust throughout than those circulation.