Journal ArticleThe Pliocene Model Intercomparison Project Phase 2: large-scale climate features and climate sensitivityHaywood, Alan M.; Tindall, Julia C.; Dowsett, Harry J.; Dolan, Aisling M.; Foley, Kevin M.; Hunter, Stephen J.; Hill, Daniel J.; Chan, Wing-Le; Abe-Ouchi, Ayako; Stepanek, Christian; Lohmann, Gerrit; Chandan, Deepak; Peltier, W. Richard; Tan, Ning; Contoux, Camille; Ramstein, Gilles; Li, Xiangyu; Zhang, Zhongshi; Guo, Chuncheng; Nisancioglu, Kerim H.; Zhang, Qiong; Li, Qiang; Kamae, Youichi; Chandler, Mark A.; Sohl, Linda E.; Otto-Bliesner, Bette L.; Feng, Ran; Brady, Esther C.; von der Heydt, Anna S.; Baatsen, Michiel L.; Lunt, Daniel J.nullAbstract. The Pliocene epoch has great potential to improve ourunderstanding of the long-term climatic and environmental consequences of an atmospheric CO2 concentration near ∼400 parts permillion by volume. Here we present the large-scale features of Plioceneclimate as simulated by a new ensemble of climate models of varyingcomplexity and spatial resolution based on new reconstructions ofboundary conditions (the Pliocene Model Intercomparison Project Phase 2;PlioMIP2). As a global annual average, modelled surface air temperaturesincrease by between 1.7 and 5.2 ∘C relative to the pre-industrial erawith a multi-model mean value of 3.2 ∘C. Annual mean totalprecipitation rates increase by 7 % (range: 2 %–13 %). On average, surface air temperature (SAT) increases by 4.3 ∘C over land and 2.8 ∘C over the oceans. There is a clear pattern of polar amplification with warming polewards of 60∘ N and 60∘ S exceeding the global mean warming by a factor of 2.3. In the Atlantic and Pacific oceans, meridional temperature gradients are reduced, while tropical zonal gradients remain largely unchanged. There is a statistically significant relationship between a model's climate response associated with a doubling in CO2 (equilibrium climate sensitivity; ECS) and its simulated Pliocene surface temperature response. The mean ensemble Earth system response to a doubling of CO2 (including ice sheet feedbacks) is 67 % greater than ECS; this is larger than the increase of 47 % obtained from the PlioMIP1 ensemble. Proxy-derived estimates of Pliocene sea surface temperatures are used to assess model estimates of ECS and give an ECS range of 2.6–4.8 ∘C. This result is in general accord with the ECS range presented by previous Intergovernmental Panel on Climate Change (IPCC) Assessment Reports.2020-01-0110280510Climate of the Past1662095 to 21231814-9332https://doi.org/10.5194/cp-16-2095-20201903650National Science Foundation