A new study has determined that global warming could actually chill down North America within a few decades.
According to a report in National Geographic News, the study, led by Tim Daley of Swansea University in the UK, looked into a sudden cooling event that gripped the North American region about 8,300 years ago.
AdvertisementAnalysis of ancient moss from Newfoundland, Canada, links an injection of freshwater from a burst glacial lake to a rapid drop in air temperatures by a few degrees Celsius along North America's East Coast.
This event created a colder year-round climate with a much shorter growing season for about 150 years, from northern Canada to what is now Cape Hatteras, North Carolina.
The results suggest that North America's climate is highly sensitive to meltwater flowing into the ocean, according to Daley.
The work also means that history could repeat itself. Currently, Greenland's ice sheet is melting at a rapid clip, releasing freshwater into the North Atlantic.
Daley and colleagues studied mosses dating back more than 8,700 years that were preserved in a Newfoundland peat bog.
The ratios of two different types of oxygen in the mosses allowed the team to trace changes in atmospheric temperature over time.
When air temperatures are lower, the mosses contain less oxygen-18, a heavier version of the more common type, oxygen-16.
About 8,350 years ago, the amount of oxygen-18 relative to oxygen-16 suddenly dropped.
Previous research had found that, around the same time, a northern ice dam burst, releasing the contents of a vast glacial lake into the Labrador Sea, between Canada and Denmark.
Normally, a warm ocean current called the Gulf Stream runs up the east coast of North America, helping to keep the region balmier than it should be, considering how far north it is.
But, the entire glacial lake drained within less than a year, injecting a huge pulse of freshwater into the North Atlantic Ocean.
According to Daley and colleagues, the lake water diluted the salty ocean current and slowed the Gulf Stream, which in turn led to rapid cooling in North America.
"As a result, Canadian summer temperatures would have been similar to those currently experienced in autumn or spring," said team member Neil Loader, also of Swansea University.
As for whether today's melt in Greenland could trigger another round of cooling, Hans Renssen, a climate researcher at Vrije University in Amsterdam, said that he doesn't believe the change would be as dramatic as last time.