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[1] The behavior of the Hadley cell and the thermodynamic structure of the tropical atmosphere is analyzed over the period 1979–2000 in climate models and reanalyses. Significant trends in the strength of the Hadley cell are present in reanalyses that are not reproduced by models. Analysis of the thermodynamic structure also shows significant discrepancies between models and reanalyses, the former show warming aloft and increased static stability while the latter show a cooling trend and decreased static stability in the tropical mid-troposphere. Additional energy balance analysis reveals that models and reanalyses have a fundamentally different balance between diabatic heating, circulation and thermodynamic structure over the period 1979–2000. Uncertainties in the observations of tropospheric temperatures as well as potential biases and errors in the climate models raise questions about the true long-term behavior of the thermodynamic structure of the tropical troposphere and the Hadley cell.