New measurements in the Antarctic show the sea ice is much thicker in places than previously thought. Does this tell us anything about global warming?
Measurements conducted by an underwater robot have found that Antarctic sea ice is much thicker in some places than previously thought. Much of this floating sea ice is under water, hidden from the satellites which have been tracking seasonal sea ice for decades. The satellite data is usually confirmed by drilling into ice floes which can be reached by ship or by visual estimates from the ships. But even then it's difficult to reach the thickest ice that way.
Underwater robot below the ice
Over the last four years, an international group of researchers has been mapping the bottom of sea ice in several areas of the Antarctic, using an underwater robot (AUV). The device can swim to a depth of some 30 meters (100 feet) and uses sonar directed upwards to survey the bottom of the sea ice. This provides access to areas where, until now, measurements could not been carried out.
The study, published in the journal Nature Geoscience, suggests that the average ice thickness could be considerably higher than previous estimates. In three regions surveyed, the robot sub found that deformed, thickened ice accounted for at least half of and as much as 76 percent of the total ice volume, the researchers say.
Climate skepticism vindicated?
While Antarctica's ice sheet, that is the land ice, is melting and retreating, the extent of the sea ice has been expanding over the last three winters. This has led some climate change skeptics to suggest that it could be evidence that human-made global warming isn't happening. But sea-ice physicist Stefan Hendricks, from the Alfred-Wegener Institute for Polar and Marine Research, based in Bremerhaven, Germany, told DW the new measurements were no reason to doubt climate change.
"What our colleagues have shown is that ship-based measurements do not record this really thick ice. That's no surprise to us. It's good that they have found this out, but basically it just tells us that we have to be cautious when it comes to using ship-based data," Hendricks said.
While sea ice in the Antarctic has been growing, the sea ice in the Arctic has been decreasing dramatically in recent years. Hendricks stresses that the two regions are completely different:"The Arctic Ocean is surrounded by land, whereas in the Antarctic, the land is in the middle. If the Arctic were not surrounded by land, the ice cover would also be much bigger in winter," says Hendricks.
The increase in Antarctic sea ice in winter can be partly explained by the wind direction, he adds. The thinner ice is, the faster it created. If it's blown out from shore, for instance into the Indian Ocean, new ice is created very quickly, according to the ice expert. He also warns against comparing the Arctic during summer to the Antarctic in winter: "If you look at the cycle over the whole year, your will see that the sea ice in the Antarctic also melts almost completely in summer."
Valuable data, limited application
Still, the German expert says the new ice measurements from the Antarctic are of major importance to our understanding sea ice. But he stresses that the ice floes are on the move all the time. Although the measurements are very precise, the situation is constantly changing, and the measurements could only be taken at a limited number of spots in what is a vast area of ice.
"The question is how representative is this for the total ice extent?" Hendricks says. "This depends to a very large extent on which ice floe you take. There are large differences between them. The differences are particularly marked if you go further away from land. Close to land, the ice piles up and is deformed and so you get this very thick ice. Further out, you don't get that."
The new measurements certainly do not give any reason to be more relaxed about climate warming, says Hendricks. Increased sea ice could have a cooling effect, as ice reflects heat back into space, whereas the sea water absorbs the heat, exacerbating warming. But given that the ice melts again in summer, that effect would be very slight, says the physicist.