Global warming stopped a new ice age from starting, Science study

Global warming has halted the onset of a new ice age, according to a study published in the journal Science. The Barnes Ice Cap on Baffin Island in the Canadian Arctic had been growing for about two thousand years, but began to shrink around 1960.

The Barnes Ice Cap is the last surviving remnant of the Laurentide Ice Sheet, which covered vast areas of North America during the last glaciation. The researchers examined remains of ancient vegetation that was once buried by the advancing ice and is now being exposed as it retreats. By dating these remains and analyzing rock samples, they reconstructed how the glacier expanded and retreated over the millennia.

How the glacier grew for two thousand years

Throughout the Holocene, the ice cap gradually shrank. Between roughly 3,600 and 2,000 years ago, it was even smaller than it is today. But around two thousand years ago it began to grow again, which the study’s authors regard as the start of a new ice age.

The growth was driven by a long decline in summer sunlight in the northern latitudes, conditions in which snow survives better. The main role was played by slow changes in Earth’s orbit known as Milankovitch cycles.

A turning point around 1960

Around 1960, the glacier reached its largest size of this roughly two-thousand-year growth phase and then started to retreat. According to the study, the warming of recent decades has been so strong that it outweighed the natural, centuries-long weakening of summer solar radiation. As temperatures rise, the glacier loses more ice in summer than it can gain in winter.

“It was just getting started, everything was going as it should, the next glaciation was on its way, and yet it stopped. It’s a very telling example of how much we have interfered with the climate system,” said lead author Nicolas Young, a geochemist at the Columbia Climate School.

He cautioned that even without warming, the gradual cooling would have become noticeable only after thousands of years. By his estimate, it would have taken about 30,000 years for the Laurentide Ice Sheet to rebuild to its former continental scale.

What lies ahead for the glacier

In the past, the Barnes Ice Cap was one of the centers from which the Laurentide Ice Sheet gradually spread: the presence of ice helped create conditions for further growth. According to model projections, it could disappear entirely within the next few centuries. If this last remnant melts, a future glaciation may unfold differently from past glacial cycles. Scientists cannot yet say when the next ice age might begin.

Around Prague, based on reporting by novinky.cz