Why global warming hasn’t touched Antarctic Ocean

New York: While the world continues to grapple under the effects of global warming, researchers have found why the waters surrounding Antarctica are among the last places on Earth to be seemingly unaffected by the human-driven climate change.

The findings showed that the unique ocean currents that surround Antarctica continually pull deep and centuries-old seawater up to the surface, which last touched Earth’s atmosphere before the machine age and so has not been warmed by the atmosphere since fossil fuels began contributing to greenhouse gases.

“It’s really deep, old water that’s coming up to the surface, all around the continent. You have a lot of water coming to the surface, and that water hasn’t seen the atmosphere for hundreds of years,” said lead author Kyle Armour, assistant professor at University of Washington, in the US.

The Southern Ocean’s water comes from such great depths, and from sources that are so distant, that it will take centuries before the water reaching the surface has experienced modern global warming, the researchers said.

Other places in the oceans, like the west coast of the Americas and the equator, draw seawater up from a few hundred meters depth, but that doesn’t have the same effect.

“The Southern Ocean is unique because it’s bringing water up from several thousand meters (as much as 2 miles),” Armour added in the paper published in the journal Nature Geoscience.

The researchers used data from Argo observational floats and other instruments to trace the path of the missing heat.
Previously it was thought that heat taken up at the surface would just mix downward, and that’s the reason for the slow warming in Antartica.

“But the observations show that heat is actually being carried away from Antarctica, northward along the surface,” Armour noted.

Gale-force westerly winds that constantly whip around Antarctica act to push surface water north, continually drawing up water from below.

In the study, the team used dyes in model simulations to show that seawater that has experienced the most climate change tends to clump up around the North Pole, another reason why the Arctic’s ocean and sea ice are bearing the brunt of global warming, while Antarctica remains largely oblivious.

“The oceans are acting to enhance warming in the Arctic while damping warming around Antarctica,” Armour said.

Knowing where the extra heat trapped by greenhouse gases goes, and identifying why the poles are warming at different rates, will help to better predict temperatures in the future, the researchers said.