Nelson Institute for Environmental Studies, University of Wisconsin-Madison, Madison, WI 53706;
Department of Geography and Center for Climatic Research, University of Wisconsin-Madison, Madison, WI 53706.
Proc Natl Acad Sci U S A. 2018 Dec 26;115(52):13288-13293. doi: 10.1073/pnas.1809600115. Epub 2018 Dec 10.
As the world warms due to rising greenhouse gas concentrations, the Earth system moves toward climate states without societal precedent, challenging adaptation. Past Earth system states offer possible model systems for the warming world of the coming decades. These include the climate states of the Early Eocene (ca. 50 Ma), the Mid-Pliocene (3.3-3.0 Ma), the Last Interglacial (129-116 ka), the Mid-Holocene (6 ka), preindustrial (ca. 1850 CE), and the 20th century. Here, we quantitatively assess the similarity of future projected climate states to these six geohistorical benchmarks using simulations from the Hadley Centre Coupled Model Version 3 (HadCM3), the Goddard Institute for Space Studies Model E2-R (GISS), and the Community Climate System Model, Versions 3 and 4 (CCSM) Earth system models. Under the Representative Concentration Pathway 8.5 (RCP8.5) emission scenario, by 2030 CE, future climates most closely resemble Mid-Pliocene climates, and by 2150 CE, they most closely resemble Eocene climates. Under RCP4.5, climate stabilizes at Pliocene-like conditions by 2040 CE. Pliocene-like and Eocene-like climates emerge first in continental interiors and then expand outward. Geologically novel climates are uncommon in RCP4.5 (<1%) but reach 8.7% of the globe under RCP8.5, characterized by high temperatures and precipitation. Hence, RCP4.5 is roughly equivalent to stabilizing at Pliocene-like climates, while unmitigated emission trajectories, such as RCP8.5, are similar to reversing millions of years of long-term cooling on the scale of a few human generations. Both the emergence of geologically novel climates and the rapid reversion to Eocene-like climates may be outside the range of evolutionary adaptive capacity.
由于温室气体浓度升高导致全球变暖，地球系统正朝着没有社会先例的气候状态发展，这对适应能力构成了挑战。过去的地球系统状态为未来几十年变暖的世界提供了可能的模型系统。这些系统包括早始新世（约 5000 万年前）、中新世中期（330-300 万年前）、末次间冰期（12.9-11.6 万年前）、全新世中期（6000 年前）、工业化前（约 1850 年）和 20 世纪。在这里，我们使用 Hadley 中心耦合模型版本 3（HadCM3）、戈达德太空研究所模型 E2-R（GISS）和社区气候系统模型版本 3 和 4（CCSM）地球系统模型，定量评估未来预测的气候状态与这六个地质历史基准的相似性。在代表浓度路径 8.5（RCP8.5）排放情景下，到 2030 年，未来气候最接近中新世气候，到 2150 年，最接近始新世气候。在 RCP4.5 下，到 2040 年，气候稳定在类似于上新世的条件下。上新世和始新世气候首先出现在大陆内部，然后向外扩展。在 RCP4.5 下，地质上新颖的气候很少见（<1%），但在 RCP8.5 下，有 8.7%的地球出现这种气候，其特点是高温和高降水。因此，RCP4.5 大致相当于稳定在上新世气候，而不受控制的排放轨迹，如 RCP8.5，类似于在几个人类世代的时间尺度上逆转数百万年的长期冷却。地质上新颖的气候的出现和迅速逆转到始新世气候都可能超出进化适应能力的范围。
