ABRUPT CLIMATE CHANGE: 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. Ice core records recovered over the last 30 years from high-elevation, low-latitude ice fields, along with other proxy data, provide three primary lines of evidence for past and present abrupt climate change. First, high-resolution time series of δ¹⁸O (temperature proxy) and net balance (precipitation proxy) 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 Earth’s climate system. Finally, there is strong evidence within and around these glaciers for a widespread and spatially coherent abrupt event ~5.2 ka marking the transition from early Holocene warmth to cooler conditions that was also coincident with structural changes in several civilizations. The remarkable similarity of changes in the highland and coastal cultures of Peru and climate variability, especially precipitation, implies a strong connection between prehistoric human activities and climate in this region. Ice core data are combined with other paleoclimatic and geoarchaeological evidence to better constrain the magnitude, extent, timing and impacts of this mid-Holocene event. The nature of tropical climate variability is examined in greater detail, and new insights on ENSO and monsoon-linked climate phenomena are emerging from the new Quelccaya and Coropuna ice cores. The Quelccaya records are the “holy grail” of high resolution ice core records for tropical glaciers and clearly show that the recent acceleration of ice retreat is not driven by changes in the net mass accumulation. Well-documented ice loss on Quelccaya in the Andes, Naimona’nyi in the Himalayas and Kilimanjaro in eastern Africa paint a grim future for tropical glacier histories. The current melting of high-altitude, low-latitude ice fields is consistent with model predictions for a vertical amplification of temperature in the tropics. The ongoing glacier retreat in the Andes, Himalayas and Africa has implications for the people who live in these areas and hence are on the front lines of the climate change crisis.