The middle-to-late Eocene greenhouse climate, modelled using the CESM 1.0.5
The middle-to-late Eocene greenhouse climate, modelled using the CESM 1.0.5
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DOI：
10.5194/cp-2020-29
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发表时间：
2020-03
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影响因子：
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通讯作者：
M. Baatsen;A. S. von der Heydt;M. Huber;M. Kliphuis;P. Bijl;A. Sluijs;H. Dijkstra
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文献类型：
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作者：
M. Baatsen;A. S. von der Heydt;M. Huber;M. Kliphuis;P. Bijl;A. Sluijs;H. Dijkstra
抽象的。虽然在许多模拟研究中已经考虑了始新世早期，但目前还缺乏对始新世中期和晚期气候的详细模拟。为了更好地了解始新世-渐新世过渡期（~34 Ma）的南极冰川作用和中始新世晚期的温暖，对始新世中晚期的气候进行适当的重建至关重要。高分辨率（CMIP 5类）耦合气候模拟的结果在这里表示使用社区地球系统模式（CESM）版本1。两个中晚始新世的情况下，被认为是相同的一般边界条件，但不同的辐射强迫，使用一个新的详细的38马地理重建。在4×工业化前CO2（1120 ppm）和CH 4（~2700 ppb）浓度（PIC）下，平衡海表温度与中始新世晚期（42-38 Ma; ~Bartonian）代用指标吻合较好。在2× PIC强迫下模拟的气候总体较冷，与始新世晚期（38-34 Ma; ~Priabonian）的气候有较好的相似性。地面温度代理，虽然他们的地理覆盖范围是稀疏的，也表明，这里提出的结果是现实的。重建的38马气候有一个减少赤道到极点的温度梯度和更对称的纬向热分布相比，工业化前的参考。地理、植被和冰的共同影响造成了工业化前和38 Ma始新世边界条件之间全球平均5-7 °C的差异，其中云和水蒸气反馈起了重要作用。这些模拟有效地表明，一个现实的中晚始新世气候可以重建，而不需要温室气体浓度远高于代理估计（即约500-1200 ppm CO2）。平衡气候敏感性（0.62 °C/W m2; 38 Ma 2× PIC和4× PIC之间升温3.2 °C）与当今气候（0.79 °C/W m2; CO2加倍3.1 °C）相比有所降低。尽管在这两个38 Ma的情况下，海冰和积雪覆盖非常有限，该模式仍然显示了一个2倍的极性放大响应大气温室气体浓度的进一步增加。在模拟的始新世气候中，高纬度地区主要是通过改变辐射平衡，结合全球地理变化和与工业化前参考相比没有极地冰盖来保持温暖。
Abstract. While the early Eocene has been considered in many modelling studies, detailed simulations of the middle and late Eocene climate are currently scarce. To get a better understanding of both Antarctic glaciation at the Eocene-Oligocene transition (~34 Ma) and late middle Eocene warmth, it is vital to have an adequate reconstruction of the middle-to-late Eocene climate. Results of higher (CMIP5-like) resolution coupled climate simulations are represented here using the Community Earth System Model (CESM) version 1. Two middle-to-late Eocene cases are considered with the same general boundary conditions but a different radiative forcing, using a new detailed 38 Ma geography reconstruction. Under 4× pre-industrial concentrations (PIC) of both CO2 (i.e. 1120 ppm) and CH4 (~2700 ppb), equilibrium sea surface temperatures correspond well to the available late middle Eocene (42–38 Ma; ~Bartonian) proxies. Being generally cooler, the simulated climate under 2× PIC forcing is a good analog for that of the late Eocene (38–34 Ma; ~Priabonian). Terrestrial temperature proxies, although their geographical coverage is sparse, also indicate that the results presented here are realistic. The reconstructed 38 Ma climate has a reduced equator-to-pole temperature gradient and a more symmetric meridional heat distribution compared to the pre-industrial reference. The collective effects of geography, vegetation and ice accounts for a global mean 5–7 °C difference between pre-industrial and 38 Ma Eocene boundary conditions, with important contributions from cloud and water vapour feedbacks. These simulations effectively show that a realistic middle-to-late Eocene climate can be reconstructed without the need for greenhouse gas concentrations much higher than proxy estimates (i.e. ~500–1200 ppm CO2). Equilibrium climate sensitivity is reduced (0.62 °C/W m2; 3.2 °C warming between 38 Ma 2× PIC and 4× PIC) compared to that of the present-day climate (0.79 °C/W m2; 3.1 °C per CO2 doubling). Despite very limited sea ice and snow cover in both 38Ma cases, the model still shows a factor ~2 polar amplification in response to a further increase of atmospheric greenhouse gas concentrations. High latitudes in the modelled Eocene climate are mainly kept warm by an altered radiative balance in combination with global changes in geography and the absence of polar ice sheets compared to the pre-industrial reference.