We present the Alfred Wegener Institute's contribution to the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2) wherein we employ the Community Earth System Models (COSMOS) that include a dynamic vegetation scheme. This work builds on our contribution to Phase 1 of the Pliocene Model Intercomparison Project (PlioMIP1) wherein we employed the same model without dynamic vegetation. Our input to the PlioMIP2 special issue of Climate of the Past is twofold. In an accompanying paper we compare results derived with COSMOS in the framework of PlioMIP2 and PlioMIP1. With this paper we present details of our contribution with COSMOS to PlioMIP2. We provide a description of the model and of methods employed to transfer reconstructed mid-Pliocene geography, as provided by the Pliocene Reconstruction and Synoptic Mapping Initiative Phase 4 (PRISM4), to model boundary conditions. We describe the spin-up procedure for creating the COSMOS PlioMIP2 simulation ensemble and present large-scale climate patterns of the COSMOS PlioMIP2 mid-Pliocene core simulation. Furthermore, we quantify the contribution of individual components of PRISM4 boundary conditions to characteristics of simulated mid-Pliocene climate and discuss implications for anthropogenic warming. When exposed to PRISM4 boundary conditions, COSMOS provides insight into a mid-Pliocene climate that is characterised by increased rainfall (+0.17 mm d⁻¹) and elevated surface temperature (+3.37 ^∘C) in comparison to the pre-industrial (PI). About two-thirds of the mid-Pliocene core temperature anomaly can be directly attributed to carbon dioxide that is elevated with respect to PI. The contribution of topography and ice sheets to mid-Pliocene warmth is much smaller in contrast – about one-quarter and one-eighth, respectively, and nonlinearities are negligible. The simulated mid-Pliocene climate comprises pronounced polar amplification, a reduced meridional temperature gradient, a northwards-shifted tropical rain belt, an Arctic Ocean that is nearly free of sea ice during boreal summer, and muted seasonality at Northern Hemisphere high latitudes. Simulated mid-Pliocene precipitation patterns are defined by both carbon dioxide and PRISM4 paleogeography. Our COSMOS simulations confirm long-standing characteristics of the mid-Pliocene Earth system, among these increased meridional volume transport in the Atlantic Ocean, an extended and intensified equatorial warm pool, and pronounced poleward expansion of vegetation cover. By means of a comparison of our results to a reconstruction of the sea surface temperature (SST) of the mid-Pliocene we find that COSMOS reproduces reconstructed SST best if exposed to a carbon dioxide concentration of 400 ppmv. In the Atlantic to Arctic Ocean the simulated mid-Pliocene core climate state is too cold in comparison to the SST reconstruction. The discord can be mitigated to some extent by increasing carbon dioxide that causes increased mismatch between the model and reconstruction in other regions.

中文翻译：

---

大气-海洋-海冰-植被耦合模型COSMOS对PlioMIP2的贡献

我们介绍了阿尔弗雷德·韦格纳研究所对上新世模型比较项目第二阶段（PlioMIP2）的贡献，其中我们采用了包括动态植被方案的社区地球系统模型（COSMOS）。这项工作建立在我们对上新世模型比较项目（PlioMIP1）的第一阶段的贡献的基础上，其中我们采用了没有动态植被的相同模型。我们对PlioMIP2过去气候专刊的投入是双重的。在随附的论文中，我们比较了在PlioMIP2和PlioMIP1框架下使用COSMOS得出的结果。在本文中，我们详细介绍了我们与COSMOS合作为PlioMIP2所做的贡献。我们提供了模型和方法的描述，该模型和方法用于将重建的中新世地理（由上新世重建和天气映射计划第四阶段（PRISM4）提供）建模边界条件。我们描述了创建COSMOS PlioMIP2仿真集合的旋转过程，并介绍了COSMOS PlioMIP2中上新世核心模拟的大规模气候模式。此外，我们量化了PRISM4边界条件的各个组成部分对上新世中期模拟气候特征的贡献，并讨论了对人为变暖的影响。0.17 毫米d ^-1）和升高的表面温度（3.37  ^∘C）与工业化前（PI）相比。上新世中期核心温度异常的大约三分之二可以直接归因于相对于PI升高的二氧化碳。相比之下，地形和冰盖对上新世中期温暖的贡献要小得多，分别约为四分之一和八分之一，而非线性可以忽略不计。模拟的上新世中期气候包括明显的极地放大，子午线温度梯度减小，向北移动的热带雨带，北冰洋夏季几乎没有海冰的北冰洋以及北半球高纬度的季节性减弱。模拟的上新世中期降水模式由二氧化碳和PRISM4古地理学共同定义。我们的COSMOS模拟证实了上新世中叶系统的长期特征，其中包括大西洋中子午线运输量的增加，赤道暖池的扩展和增强以及植被覆盖的明显向极扩展。通过将我们的结果与上新世中期海表温度（SST）进行比较的结果，我们发现，如果暴露于400的二氧化碳浓度下，COSMOS可以最好地重现重建的SST。 ppmv。与SST重建相比，在大西洋到北冰洋的模拟的上新世中期核心气候状态太冷。增加二氧化碳会在某种程度上缓解这种不协调，二氧化碳会导致模型与其他区域的重建之间的失配增加。