We analyze the carbon–climate feedback in eight Earth System Models (ESMs) from phase 5 of the Coupled Model Intercomparison Project (CMIP5).We focus on tropical land carbon change and find decreases (-31.02 to -169.32 GtC K-1),indicating tropical ecosystems will release carbon as temperature warms,thus contributing to a positive feedback identified in earlier studies.We further investigate the relationship between tropical land carbon change and sensitivity of historical atmospheric CO2 growth rate to tropical temperature variability,and find a weak linear relationship.This sensitivity for most models is stronger than observed.We further use this "emergent constraint" [Cox et al.,2013] to constrain uncertainties in model-projected future carbon–climate changes,and find little effect in narrowing the model-spread,but the mean sensitivity is slightly smaller.This contrasts with earlier C4MIP results,highlighting the challenge in constraining future projections by modern observations and necessity for evaluating such relationships continuously.