Abstract Extreme temperature events, which are strongly influenced by temperature variability, are becoming increasingly dramatic under global warming. The temperature variability during past warm periods, like the Eocene and Pliocene, can provide useful analog information for our future climate. We used data from the Deep‐time Model Intercomparison Project (DeepMIP) and Pliocene Model Intercomparison Project Phase 2 (PlioMIP2) to examine changes in interannual temperature variability (ITV) and their driving mechanisms. Results show annual ITV changes were winter‐dominated, with hemispheric asymmetry. Higher Eocene ITV was driven primarily by paleogeographic changes and that the lower Pliocene ITV was forced mainly by increased atmospheric CO2. These findings imply that increased atmospheric CO2 can stabilize temperature variability in polar regions through sea ice melting but amplify tropical land variability through radiative feedback. Because the Pliocene has a land–sea distribution similar to today, it might be more relevant for understanding future climate variability than the Eocene.

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