Does Global Warming Actually Increase Antarctic Sea Ice?
People who insist that climate change isn’t happening often try to disprove it by pointing to what they see as contradictory phenomena. One example is the oft-repeated claim that there hasn’t been any global warming over the past 17 years, despite rising C02 levels. But one of their most visually compelling arguments has centered upon Antarctic sea ice, which expanded to reach record levels in 2014. If the planet really is warming, they ask, then shouldn’t the ice in the southern ocean be melting?
That interpretation tends to irk climate scientists, who point out that the Antarctic’s gain in sea ice is more than canceled out by the much larger melting of ice in the Arctic, so that the overall pattern is one of melting sea ice. (Here’s a 2014 study that lays that out.)
But now, in a new, not-yet-published paper, James Hansen, former director of the NASA Goddard Institute for Space Studies, and colleagues push back even harder. They argue that the increase in Antarctic sea ice not only doesn’t refute climate change, but actually is caused by warming.
“Our climate model exposes amplifying feedbacks in the Southern Ocean that slow Antarctic bottom water formation and increase ocean temperature near ice shelf grounding lines, while cooling the surface ocean and increasing sea ice cover and water column stability,” the scientists argue in the abstract for the paper, which is undergoing review for publication in the journal Atmospheric Chemistry and Physics.
Here’s that scenario in simpler terms. While sea ice has been increasing, we know from analyzing satellite data that the ice covering the land mass of Antarctica has been melting rapidly.
Hansen and colleagues think that as those ice shelves disintegrate, a lot of cold freshwater is draining into the Southern Ocean. That’s creating a cold surface layer that is causing sea ice to form. Underneath that, though, the salty, denser subsurface waters are still warming.
A January 2014 article on the website of the National Snow and Ice Data Center describes previous research that also points to this explanation.
"If the Southern Ocean ... subsurface warming of the Antarctic ice sheets continues to grow," Hansen and colleagues write in the study, "it likely will become impossible to avoid sea level rise of several meters, with the largest uncertainty being how rapidly it will occur."
Hansen told the Washington Post that the Antarctic ice expansion trend will continue, along with ice sheet melt. But that acceleration actually will be a sign that climate change is worsening.
“It will be clearer, give us a few more years,” Hansen told the Post.
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