The Pliocene Model Intercomparison Project Phase 2: Large-scale Climate Features and Climate Sensitivity

• Published in: Climate of the past Vol. 16; no. 6; pp. 2095 - 2123
• 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, Heydt, Anna S von der, Baatsen, Michiel L J, Lunt, Daniel H
• Format: Journal Article
• Language: English
• Published: Goddard Space Flight Center European Geosciences Union/Copernicus Publications 04.11.2020; Copernicus GmbH; European Geosciences Union (EGU); Copernicus Publications
• Subjects: Air temperature; Analysis; Annual; Annual precipitation; Atmospheric models; Boundary conditions; Carbon dioxide; Carbon dioxide atmospheric concentrations; Carbon dioxide concentration; Climate change; Climate models; Climate sensitivity; Climatology; Datasets; Earth Sciences; Environmental assessment; Experiments; Geology; Glaciation; Global temperature changes; Ice sheets; Intercomparison; Intergovernmental Panel on Climate Change; Meteorology And Climatology; Ocean circulation; Oceans; Pliocene; Precipitation; Sciences of the Universe; Sea surface; Sea surface temperature; Sensitivity; Spatial discrimination; Spatial resolution; Statistical analysis; Surface temperature; Surface-air temperature relationships; Temperature; Temperature gradients; Topography; Tropical climate; Wind; United States > US; Pliocene Model Intercomparison Project; Climate Models; Surface Air Temperature; Climate Sensitivity; Pliocene Climate; Large-Scale Climate Features
• ISSN: 1814-9324; 1814-9332; 1814-9332
• DOI: 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 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.