The Pliocene Model Intercomparison Project Phase 2: large-scale climate features and climate sensitivity

• Published in: Climate of the Past
• Main Authors: Haywood, 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, Richard W., Tan, Ning, Contoux, Camille, Ramstein, Gilles, Li, Xiangyu, Zhang, Zhongshi, Guo, Chuncheng, Nisancioglu, Kerim Hestnes, 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. J., Lunt, Daniel J
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2020
• Subjects: Pacific; Ice Sheet
• Online Access: https://hdl.handle.net/11250/2723625; https://doi.org/10.5194/cp-16-2095-2020

The Pliocene epoch has great potential to improve our understanding of the long-term climatic and environmental consequences of an atmospheric CO2 concentration near ~ 400 parts per million by volume. Here we present the large-scale features of Pliocene climate as simulated by a new ensemble of climate models of varying complexity and spatial resolution and based on new reconstructions of boundary conditions (the Pliocene Model Intercomparison Project Phase 2; PlioMIP2). As a global annual average, modelled surface air temperatures increase by between 1.4 and 4.7 °C relative to pre-industrial with a multi-model mean value of 2.8 °C. Annual mean total precipitation rates increase by 6 % (range: 2 %–13 %). On average, surface air temperature (SAT) increases are 1.3 °C greater over the land than over the oceans, and 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 2.4. In the Atlantic and Pacific Oceans, meridional temperature gradients are reduced, while tropical zonal gradients remain largely unchanged. Although there are some modelling constraints, 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 doubling of CO2 (including ice sheet feedbacks) is approximately 50 % greater than ECS, consistent with results from the PlioMIP1 ensemble. Proxy-derived estimates of Pliocene sea-surface temperatures are used to assess model estimates of ECS and indicate a range in ECS from 2.5 to 4.3 °C. This result is in general accord with the range in ECS presented by previous IPCC Assessment Reports. publishedVersion