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

• Published in: Climate of the Past
• Main Authors: A. M. Haywood, J. C. Tindall, H. J. Dowsett, A. M. Dolan, K. M. Foley, S. J. Hunter, D. J. Hill, W.-L. Chan, A. Abe-Ouchi, C. Stepanek, G. Lohmann, D. Chandan, W. R. Peltier, N. Tan, C. Contoux, G. Ramstein, X. Li, Z. Zhang, C. Guo, K. H. Nisancioglu, Q. Zhang, Q. Li, Y. Kamae, M. A. Chandler, L. E. Sohl, B. L. Otto-Bliesner, R. Feng, E. C. Brady, A. S. von der Heydt, M. L. J. Baatsen, D. J. Lunt
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2020
• Subjects: Environmental pollution; TD172-193.5; Environmental protection; TD169-171.8; Environmental sciences; GE1-350; Pacific; Ice Sheet
• Online Access: https://doi.org/10.5194/cp-16-2095-2020; https://doaj.org/article/e324750e9a7743cc94547358d398759f

The Pliocene epoch has great potential to improve our understanding of the long-term climatic and environmental consequences of an atmospheric CO 2 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 CO 2 (equilibrium climate sensitivity; ECS) and its simulated Pliocene surface temperature response. The mean ensemble Earth system response to a doubling of CO 2 (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.