Researchers have shown through a new study that a warming climate is capable of melting away ice sheets as large as Greenland’s.
According to a study published in Journal Science, warming of the climate led to massive reduction in mass of the Cordilleran Ice Sheet – almost by half in as little as 500 years – and based on these findings, researchers believe that global warming could bring about a similar fate for Greenland Ice Sheet.
During the Last Ice Age or Pleistocene, the Cordilleran Ice Sheet covered large parts of North America and had mass similar to that of the Greenland Ice Sheet. Estimates indicate that the sheet covered most parts of western Canada some 12,500 years ago, but new data shows that large areas in the region were ice-free as early as 1,500 years earlier. This confirms that once ice sheets start to melt, they can do so very quickly.
Scientists believe that the massive melting of the Cordilleran Ice Sheet would have caused increase in sea levels by up to 20 feet and could have also induced changes in ocean temperature and circulation. Because cold water is denser than warm water, the water contained by ice sheets sinks when it melts, disrupting the “global conveyor belt” of ocean circulation and changing climate.
Researchers used geologic evidence and ice sheet models to construct a timeline of the Cordilleran’s advance and retreat. They mapped and dated moraines throughout western Canada using beryllium-10, a rare isotope of beryllium that is often used as a proxy for solar intensity. Measurements were made in Purdue University’s PRIME Lab, a research facility dedicated to accelerator mass spectrometry.
Around 14,000 years ago the Earth started warming, and the effects were significant – ice completely left the tops of the mountains in western Canada, and where there were ice sheets, they probably thinned a lot. About a thousand years later, the climate cooled again, and glaciers started to advance, then retreated as conditions warmed at the onset of the Holocene. If the Cordilleran Ice Sheet had still been there when the climate started cooling during a period known as the Younger Dryas, cirque and valley glaciers wouldn’t have advanced during that time. This indicates a rapid disappearance rather than a gradual melting of the ice sheet.
Reconstructing precise chronologies of past climate helps researchers establish cause and effect. Some have wondered whether the melting of the Cordilleran Ice Sheet caused the Younger Dryras cooling, but it’s unlikely; the cooling started too early for that to be true, according to the study. What caused the cooling is still up for debate.
Creating a timeline of glacial retreat also provides insight into how the first people got to North America. Current estimates place human migration to the south of the Cordilleran and Laurentide Ice Sheets between 14,600 and 18,000 years ago, but how they got there isn’t clear. Some say humans could have crossed through an opening between the ice sheets, but these new findings show that passage was likely closed until 13,400 years ago.