Data from: A glimpse of an extremely warm world - lessons from the Early Paleogene

As the world warms, the Earth system moves towards a climate state without
societal precedent. This challenges future predictions, as climate models
need to be tested and calibrated with real-world data.  One
strategy for assessing the effects of greenhouse forcing on climate is to
turn to Earth’s past, where changes in climate are stored in the form of
sedimentological, paleontological, isotopic, and geochemical proxies. We
compile global proxy data across multiple global warming events of the
early Paleogene (66-47.8 Ma) – a period of extreme warmth suggested as a
possible analogue for worst-case scenarios of future global warming. We
take a novel, multi-proxy approach where we include information on
precipitation intermittency and intensity, and integrate the proxies into
climate types. The data show surprising hydrological shifts that started
well before and persisted well beyond the Paleocene-Eocene Thermal Maximum
– the warmest period of the Cenozoic Era and the focus of much of the
prior research. We provide a glimpse of an extremely warm world with
ever-wet or monsoonal conditions in the polar regions and aridity
interrupted by extreme rainfall at mid-latitude continental interiors. We
show that extremely warm climates may induce (1) non-linearities in the
hydrological cycle’s sensitivity to temperature increase, (2) departures
from the wet-gets-wetter and dry-gets-drier response, and (3) a decoupling
of mean annual precipitation from precipitation intensity and
intermittency. Our results are inconsistent with vegetation boundary
conditions and precipitation outcomes from state-of-the-art paleoclimate
modeling. Our focus on precipitation intermittency and intensity provides
a new perspective on future trends in climate under extremely warm
conditions.

随着全球变暖，地球系统正迈向一种无前例可循的气候状态。这给未来气候预测带来挑战，因为气候模型需要依托真实观测数据进行检验与校准。评估温室强迫对气候影响的一种策略，便是回溯地球过往——气候变迁以沉积学、古生物学、同位素及地球化学代用指标（proxy）的形式留存于地质记录之中。我们汇编了古近纪早期（66-47.8百万年前）多次全球变暖事件的全球代用指标数据集，该时期曾经历极端暖期，被认为是未来全球变暖最坏情景的潜在类比参照。本研究采用创新的多代用指标研究路径，纳入降水间歇性与降水强度相关数据，并将代用指标整合至气候类型分类体系中。数据集揭示了令人意外的水文循环变化：这类变化早在古新世-始新世极热事件（Paleocene-Eocene Thermal Maximum，新生代最暖时期，亦是既往多数研究的核心关注点）之前便已启动，并在该事件结束后仍持续了相当长的时间。我们得以窥见极端暖期地球的样貌：极地地区呈现持续湿润或季风性气候特征，而中纬度大陆内陆则在干旱背景下穿插极端降雨事件。本研究表明，极端暖气候可能引发三类变化：(1) 水文循环对温度升高的敏感性呈现非线性特征；(2) 气候响应偏离“湿区更湿、干区更干”的经典规律；(3) 年平均降水量与降水强度、降水间歇性出现解耦现象。本研究结果与当前最先进古气候模拟得到的植被边界条件及降水模拟结果存在不一致之处。我们针对降水间歇性与降水强度的研究视角，为极端暖气候背景下的未来气候趋势提供了全新的解读维度。