The impact of different atmospheric CO2 concentrations on large scale Miocene temperature signatures
Based on inferences from proxy records the Miocene (23.03–5.33 Ma) was a time of amplified polar warmth compared to today. However, it remains a challenge to simulate a warm Miocene climate and pronounced polar warmth at reconstructed Miocene CO2 concentrations. Using a state-of-the-art Earth-System-Model, we implement a high-resolution paleobathymetry and simulate Miocene climate at different atmospheric CO2 concentrations. We estimate global mean surface warming of +3.1 °C relative to the preindustrial at a CO2 level of 450 ppm. An increase of atmospheric CO2 from 280–450 ppm provides an individual warming of ∼1.4 °C, which is as strong as all other Miocene forcing contributions combined. Substantial changes in surface albedo are vital to explain Miocene surface warming. Simulated surface temperatures fit well with proxy reconstructions at low- to mid-latitudes. The high latitude cooling bias becomes less pronounced for higher CO2. At higher CO2 levels simulated Miocene climate shows a reduced polar amplification, linked to a breakdown of seasonality in the Arctic Ocean. A pronounced warming in boreal fall is detected for a CO2 increase from 280–450 ppm, in comparison to weaker warming for CO2 changes from 450–720 ppm. Moreover, a pronounced warming in winter is detected for a CO2 increase from 450–720 ppm, in contrast to a moderate summer temperature increase, which is accompanied by a strong sea-ice concentration decline and enhanced moisture availability promotes cloud formation in summer. As a consequence planetary albedo increases and dampens the temperature response to CO2 forcing at a warmer Miocene background climate.
Publication titlePaleoceanography and Paleoclimatology
Department/SchoolInstitute for Marine and Antarctic Studies
PublisherWiley-Blackwell Publishing Inc.
Place of publicationUnited States
Rights statement© 2023 The Authors. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) License, https://creativecommons.org/licenses/by-nc/4.0/ which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.