AGU: Last Remnant Of North American Ice Sheet Likely To Disappear In 300 Years

AGU News:
WASHINGTON, D.C. — The last remaining piece of the vast ice sheet that once covered North America is doomed to vanish in the next few centuries, a new study finds.
Rising temperatures in the Arctic have caused the Barnes Ice Cap to melt at an extraordinary pace, and nothing short of removing carbon dioxide from the atmosphere can prevent it from completely disappearing, according to a new study modeling the ice cap’s behavior.
Under a business-as-usual greenhouse gas emissions scenario, the study’s authors project the ice cap will disappear within the next 300 years. For even the most conservative greenhouse gas trajectories where emissions decline substantially after 2020, the ice cap will still disappear in less than 500 years, according to the study. To see video footage of the Barnes Ice Cap, go here.
The results provide compelling evidence that the current level of warming is almost unheard of in the past 2.5 million years, according to the study’s authors.
“This is the disappearance of a feature from the last glacial age, which would have probably survived without anthropogenic greenhouse gas emissions,” said Adrien Gilbert, a glaciologist at Simon Fraser University in British Columbia, Canada, and lead author of the new study published in Geophysical Research Letters, a journal of the American Geophysical Union.
Melting of the Barnes Ice Cap would likely have negligible impacts on sea level rise or the environment, but its end could herald the dissolution of larger ice sheets, according to the study’s authors.
“The fact that it’s disappearing is a minor scientific curiosity,” said Gifford Miller, a glacial geologist at the University of Colorado Boulder and co-author of the new study. “But its disappearance carries information about the really big ice caps. Given enough time on the path we’re currently following, then large portions of the Greenland Ice Sheet may also be at risk of disappearing, and that’s a big deal.”
Melting at a not-so-glacial pace
The Laurentide Ice Sheet covered millions of square miles of North America episodically since the start of the Quaternary Period roughly 2.5 million years ago. The ice sheet grew and shrank over time as Earth went through various climate cycles, but started retreating around 14,000 years ago when Earth’s climate warmed considerably. The receding ice stabilized about 2,000 years ago as the Barnes Ice Cap, a Delaware-sized chunk of ice on Baffin Island in the Canadian Arctic.
The Barnes Ice Cap remained the same size for the past 2,000 years until the effects of recent warming caught up with it.
Miller was doing research on Baffin Island in 2009 when he realized the ice cap had noticeably shrunk compared to images of it from a few decades ago. He then recruited Adrien Gilbert and Gwenn Flowers from Simon Fraser University to develop a model for determining how the ice cap might behave in the future.
In the new study, the researchers used the model to estimate when the ice cap would disappear under different greenhouse gas emissions scenarios. They found the ice cap is melting at all elevations and they project it to be gone within 200-500 years under all future emissions scenarios.
The researchers also collected rock samples around the ice cap to determine whether it had shrunk to a similar size at other times during its history.
They found it to be extremely rare for the Barnes Ice Cap to completely disappear, even during warm interglacial periods. The rock samples showed the ice cap shrunk to its current size only three times and disappeared no more than twice in the past 2.5 million years.
What’s most unusual about the ice cap’s situation is that it is now melting when the summer sun is weakest: Earth is currently as far from the sun as it can get during the Northern Hemisphere’s summer, Miller said.
“The geological data is pretty clear that [the Barnes Ice Cap] almost never disappears in the interglacial times,” he said. “The fact that it’s disappearing now says we’re really outside of what we’ve experienced in a two-and-a-half million-year interval and we’re entering a new climate state.”
The new study is yet another demonstration that humans are pushing the Earth system outside of conditions that have existed over the last million years, said Richard Alley, a glaciologist and climate scientist at Pennsylvania State University in State College, Pennsylvania, who was not connected to the study.
“We have very high scientific confidence that almost all the glaciers on Earth are shrinking, because of warming that is primarily being caused by our greenhouse gases,” he said.