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Canadian Study Sees Global Warming for Centuries

by Jeffrey Jones

CALGARY, Alberta - Carbon dioxide already emitted into the atmosphere will keep contributing to global warming for centuries, eventually causing a huge Antarctic ice sheet to collapse and lift sea levels, Canadian scientists said on Sunday.

Even the complete abandonment of fossil fuels and halt to emissions cannot prevent devastating ocean warming in Antarctica as well as increasing desertification in North Africa, the research finds.

Even so, many of the negative consequences in the Northern Hemisphere, such as loss of Arctic sea ice, are reversible. That means global efforts to cut greenhouse gases are not a waste of effort and money, said Shawn Marshall, a University of Calgary geography professor and one of the study's authors.

"But there are some parts of the climate that have a lot of inertia and it will take many centuries before they start to reverse," said Marshall.

The study, led by Nathan Gillett of the Canadian Centre for Climate Modelling and Analysis, is published in the journal Nature Geoscience.

Using simulations with a climate model, the scientists estimated the effects on climate patterns for the next 1,000 years by stopping emissions completely in 2010 and in 2100.

Major differences of the impacts in various regions lie in the centuries it takes for heat to circulate from the North Atlantic through the world's ocean currents and into the deep sea, Marshall said.

"The atmosphere cools pretty quickly when atmospheric gases go down and surface water will cool, but that doesn't reach the deeper waters of the ocean for a long time," he said.

Wind currents in the southern hemisphere may also play a role.

As a result, in the next 1,000 years, the average ocean temperature around Antarctica could rise by as much as 5 degrees Celsius, triggering the collapse of the West Antarctic ice sheet, according to the study.

The elimination of the ice sheet, which covers an area about the size of Texas and is up to 4,000 meters (13,120 feet) thick, could raise sea levels by several meters.

The climate impacts would also dry out the land in parts of North Africa by up to 30 percent.

Simulations show big differences in some parts of the world, however, between cutting emissions in 2010 and in 2100, including long-term temperature variations between 1 and 4 degrees Celsius, an argument for action on carbon dioxide, Marshall said.

"You sometimes hear that defeatist argument that it's too late and there are a lot of changes that are going to happen, so just worry about adaptation," he said. "But I think you do see a big divergence in potential futures depending on if there are some reductions in emissions."

(Editing by Frank McGurty)

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