Did You Know? Tropical Glacier Melt Started at the End of the Last Ice Age

Tropical glaciers in South America and Africa started retreating simultaneously at the end of the last Ice Age - about 20,000 years ago, according to a Dartmouth study.

The research, published in Science Advances, backs the exceptional scientific consensus on the role of carbon dioxide in making climate change but adds further levels of complexity to understanding Earth's climate and how ice age suddenly end.

"Carbon dioxide [caused] the Earth to [get] out of the last ice age," according to Meredith Kelly, an associate professor in the Department of Earth Sciences at Dartmouth, and lead author on the study. 

"[There] are also [previous] processes before carbon dioxide increased that are important to the story how the period ended, and that's what we wanted to [know]," Kelly added.

Glaciers in tropical Africa and South America reached their maximum extents about 29,000-21,000 years ago and then began to melt, according to the Dartmouth study. The retreat is earlier than the notable rise in carbon dioxide recorded roughly 18,200 years ago.

The findings show a trend of increasing tropical temperatures over the planet and recommend that global warming may have caused by the decline in the temperature variations between the Earth's polar regions and the tropics.

"Just a [few thousands of years] could make all the difference in our [perception] of [previous and present] climate change events," says Margaret Jackson, one of the study's authors. "This [research] shows that [icebers] were [reacting] to [global warming] even before the deglacial [increase] in carbon dioxide [which fueled] the planet over the edge to end the last ice age," she added.

The study's further findings - in addition to simultaneous, pan-tropical warming - that tropical glaciers stretched their maximum limits at the same time as glaciers at higher latitudes.

The study was conducted on glacial moraines in the Rwenzori Mountains - located on the border between Uganda and the Democratic Republic of Congo. Mountain glaciers, particularly those found at high elevations in tropical regions, are sensitive to changes in temperature. The study used the past extents of tropical glaciers to infer recent changes in tropical temperatures.

Previous research indicated that a few tropical icecaps achieved their greatest extents during the peak of the last ice age. However, the findings were just limited to South America. The Dartmouth study recalculated the pre-determined data obtained from sites over tropical South America. The study extended the results to tropical East Africa to prove that glacier loss during this period was a pan-tropical phenomenon.

"We [understood] from past work that tropical icebergs in South America may have [left] early, but we didn't know how [extensive] the phenomenon was. The Rwenzori Mountains [confirmed] to be the perfect outdoor laboratory to [verify] the pan-tropical timing of past climate change," said Jackson.

The study also supports researchers comprehend how atmospheric circulation, ocean circulation, temperature gradients, and greenhouse gasses work closely to make the planet "flip" between cold and warm periods.

"[Earth is currently] entering a new climate model that is [uncommon] in the last millions of years," said Kelly. "Models of [past events] could help us predict the future, and our more [comprehensive] understanding of the tropics serves as an important piece of [the] puzzle," Kelly added.