Retrieving a “Weather Balloon” from the last Ice Age

Abstract

“How cold was the last ice age?” is a question that paleoclimate scientists have been trying to answer for decades. Constraining the magnitude of climate change since the Last Glacial Maximum (∼20,000 years ago) can help improve our understanding of Earth's climate sensitivity and, therefore enhance our ability to predict future change (Tierney et al., 2020). Of course, there is no single answer to this question: there is spatial structure to LGM temperature change that is linked to fundamental climate system properties and processes. Consequently, paleoclimate scientists have focused on variations of this question, like “What was the latitudinal gradient of LGM temperature change?” (Chiang et al., 2003), “What was the land-sea contrast?” (Rind & Peteet, 1985) or “What was the change in ocean heat content?” (Bereiter et al., 2018). These questions inform large-scale atmospheric and oceanic circulation, the intensity of the water cycle, and planetary energy balance; the answers to these questions come from proxies like planktic and benthic foraminifera, speleothems, ice cores, pollen records, ancient groundwater, lake sediments, and glacial moraines, to name a few. In short, the paleoclimate community has developed a proxy “tool kit” equipped to map changes across the Earth's surface and into the ocean interior; but, until now, no “tool” existed for the upper atmosphere.