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, 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. J., Lunt, Daniel J.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Copernicus 2020
• Subjects: Pacific; Ice Sheet
• Online Access: https://epic.awi.de/id/eprint/53211/; https://doi.org/10.5194/cp-16-2095-2020; https://hdl.handle.net/10013/epic.7682ac44-6a28-4805-9b15-71f3e075b445

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 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 1.7 and 5.2 °C relative to the pre-industrial era with a multi-model mean value of 3.2 °C. Annual mean total precipitation 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.