THE CLIMATIC CHANGES RESPONSIBLE FOR THE DISAPPEARANCE OF TROPICAL MOUNTAIN GLACIERS AND THE SOCIETAL CONSEQUENCES

Records of stable isotopes, dust, chemistry and net balance from temperate and tropical ice cores offer long-term perspectives on precipitation, temperature, aridity and atmospheric circulation that are unavailable from other proxy sources. These data allow detailed reconstruction of both climate variability and forcing as well as timing of the most recent glaciations at different latitudes and altitudes. The resulting analyses, as well as glacier area and volume measurements, provide critical perceptions of modern climate change and the potential economic and social impacts of dwindling water resources on glacier-dependent nations. Much of the climatic activity of significance to humanity occurs between 30^oN and 30^oS, where nearly 50% of Earth’s surface lies and 70% of its inhabitants live. Therefore, it is imperative that we attain a better grasp of the climatic factors that control recent low-latitude glacier responses, especially the extensive ice fields on and surrounding the Third Pole and in the Andes of Peru. Centered on the Tibetan Plateau and Himalayas, the Third Pole covers 5 million km² and contains one of the largest glacier stores of fresh water that feeds Asia’s largest rivers. The Peruvian Andes contains over 70% of the tropical glaciers on Earth, which are critical for municipal water supplies, hydroelectricity and irrigation.

Recent data on the concomitant loss of ice on the Third Pole, the Andes, Kilimanjaro in eastern Africa and the ice fields in Papua, Indonesia reinforce the hypothesis that large-scale tropical processes dominate recent glacier retreat. This can be placed within a longer-term perspective by observing the changes in the glacier margins of the Quelccaya ice cap in Peru. ¹⁴C dates on recently collected wetland plants exposed by the recession of Quelccaya indicate that its surface area is the smallest in over 6,000 years. These observations are augmented by ¹⁴C dates from plants collected in 2015. The observed widespread melting of low to mid-latitude glaciers is consistent with model predictions of a vertical amplification of temperature, which is documented by increasing isotopic enrichment in ice cores and accelerating rates of ice loss from the highest mountains. In addition to societal impacts, such a loss will eventually obliterate most non-polar glacier climate histories.