Simulating Miocene Warmth: Insights From an Opportunistic Multi‐Model Ensemble (MioMIP1). Issue 5 (24th May 2021)

• Record Type: Journal Article
• Authors: Burls, N. J.; Bradshaw, C. D.; De Boer, A. M.; Herold, N.; Huber, M.; Pound, M.; Donnadieu, Y.; Farnsworth, A.; Frigola, A.; Gasson, E.; von der Heydt, A. S.; Hutchinson, D. K.; Knorr, G.; Lawrence, K. T.; Lear, C. H.; Li, X.; Lohmann, G.; Lunt, D. J.; Marzocchi, A.; Prange, M.; Riihimaki, C. A.; Sarr, A.‐C.; Siler, N.; Zhang, Z.
• Is Part Of: Paleoceanography and paleoclimatology. Volume 36:Issue 5(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-05-24
• Subjects: Miocene -- Miocene surface temperature synthesis -- model intercomparison -- paleoclimate -- polar amplification; Paleoceanography -- Periodicals; Paleoclimatology -- Periodicals; 551.46
• DOI: 10.1029/2020PA004054
• Languages: English
• ISSNs: 2572-4517

Abstract

Abstract: The Miocene epoch, spanning 23.03–5.33 Ma, was a dynamic climate of sustained, polar amplified warmth. Miocene atmospheric CO2 concentrations are typically reconstructed between 300 and 600 ppm and were potentially higher during the Miocene Climatic Optimum (16.75–14.5 Ma). With surface temperature reconstructions pointing to substantial midlatitude and polar warmth, it is unclear what processes maintained the much weaker‐than‐modern equator‐to‐pole temperature difference. Here, we synthesize several Miocene climate modeling efforts together with available terrestrial and ocean surface temperature reconstructions. We evaluate the range of model‐data agreement, highlight robust mechanisms operating across Miocene modeling efforts and regions where differences across experiments result in a large spread in warming responses. Prescribed CO2 is the primary factor controlling global warming across the ensemble. On average, elements other than CO2, such as Miocene paleogeography and ice sheets, raise global mean temperature by ∼2°C, with the spread in warming under a given CO2 concentration (due to a combination of the spread in imposed boundary conditions and climate feedback strengths) equivalent to ∼1.2 times a CO2 doubling. This study uses an ensemble of opportunity: models, boundary conditions, and reference data sets represent the state‐of‐art for the Miocene, but are inhomogeneous and not ideal for a formal intermodel comparison effort. Acknowledging this caveat, this study is nevertheless the first Miocene multi‐model, multi‐proxy comparison attempted so far. This study serves to take stock of the current progress toward simulating Miocene warmth while isolating remaining challenges that may be well served by community‐led efforts to coordinate modeling and data activities within a common analytical framework. Plain Language Summary: As human activity continues to increase atmospheric carbon dioxide concentrations, scientists turn to warm intervals in Earth's history to develop insight into the behavior of the climate system under elevated carbon dioxide and temperature. One such interval is the Miocene epoch which has become increasingly relevant as reconstructions of Miocene atmospheric CO2 concentrations point to values ranging between current concentrations of ∼400 ppm and those projected for the end of this century under Shared Socioeconomic Pathways 3 and 4. In this study, we evaluate the surface warming patterns simulated by a range of different climate models configured with Miocene paleogeography and CO2 concentrations spanning 200–850 ppm. We also synthesize available Miocene surface temperature reconstructions. The primary factor controlling the amount of global warming seen across the Miocene simulations analyzed is the CO2 concentration that was prescribed within a given simulation. On average, Miocene elements other than CO2, such as Miocene paleogeography and ice sheets, raise global mean temperature by ∼2°C. While some Miocene simulations with high CO2 forcing overlap with the reconstructed global mean surface temperature estimates for their target Miocene interval, they still generally fail to capture the reconstructed pattern of warming. Key Points: A synthesis of Miocene modeling efforts, and surface temperature reconstructions, is presented within a single analysis framework Miocene global mean surface temperature estimates span ∼5.3°C–11.5°C higher than preindustrial, only ∼2°C is explained by non–CO2 boundary conditions in climate models Some simulations overlap with reconstructed global mean surface temperature estimates but fail to capture the weak temperature gradient