Retreating Glaciers: A Paleoclimate Perspective from the World's Highest Mountains

Glaciers are among the first responders to global warming, serving both as indicators and drivers of climate change. Over the last 30 years the Ice Core Paleoclimate Research Group at The Ohio State University has been engaged in a program of systematic recovery of ice cores from high-elevation, low-latitude ice fields. The resulting climate records, along with other proxy data, have produced three primary lines of evidence for past and present abrupt climate change. First, high-resolution time series of d¹⁸O (temperature proxies) and net balance (precipitation proxies) demonstrate that the current warming at high elevations in the mid- to lower latitudes is unprecedented for at least the last two millennia. Second, the continuing retreat of most mid to low-latitude glaciers, many having persisted for thousands of years, signals a recent and abrupt change in the Earth's climate system. Finally, there is strong evidence within and around glaciers for a widespread and spatially coherent abrupt event ~5.2 ka that marked the transition from early Holocene warmth to cooler conditions that occurred through much of the world and was coincident with structural changes in several civilizations. Together, these three lines of evidence argue that the present warming and associated glacier retreat are unprecedented in many areas for at least 5000 years. The ice core evidence of the mid-Holocene event will be compared to available lake histories to get a larger scale understanding of both the magnitude and timing of this event.