September 18, 2013
Global Warming Could Explain Exponential Sea Ice Growth
Michael Harper for redOrbit.com - Your Universe Online
In a bit of strange and unprecedented good news, it was recently discovered Antarctic sea ice is growing at record rates. This is definitely odd, of course, because the air and the oceans have been getting warmer in the area.
There is now more sea ice in Antarctica than there had been in the 1970s, a data point which University of Washington (UW) researcher Jinlun Zhang wanted to unpack and investigate. According to his National Science Foundation-funded research, global warming might be responsible for this record increase of sea ice. This is particularly ironic considering those who disagree with global warming often use this exponential increase as an argument against climate change.
Zhang, an oceanographer at the UW Applied Physics Laboratory, now has his research published in the Journal of Climate.
“The overwhelming evidence is that the Southern Ocean is warming,” said Zhang in a statement about his research. “Why would sea ice be increasing? Although the rate of increase is small, it is a puzzle to scientists.”
According to Zhang’s research, westerly winds blowing around the South Pole have been getting stronger, thereby accounting for an 80 percent increase of sea ice over the past 30 years. It isn’t just strong winds creating this ice, says Zhang. These gusts are also merging the existing sheets of ice together to cause ridging. This, in turn, leaves wider areas of surface water exposed to the cold wind. This water then freezes, breaks apart, and is merged into existing ice. The end result, says Zhang, is much thicker formations of ridged ice and exponential ice formation.
The UW researcher built a computer model with all this information and found these interactions and chain reactions have been creating thick sea ice at about 1 percent growth per year. These sheets, measuring about 6 feet deep, have been growing at a steady rate since at least 1979 when satellite records began. As this ice continues to grow, the amount of thin ice has remained stable over the past three decades. This thick ice production is especially important, says Zhang, because it’s able to last longer through the warm summers.
“You’ve got more thick ice, more ridged ice, and at the same time you will get more ice extent because the ice just survives longer,” said the researcher.
Using the same computer model, Zhang adjusted the wind data and kept them at a constant level throughout the years. This resulted in an increase in sea ice, but only by 20 percent.
In previous studies Zhang has also hypothesized that denser water in the Southern Ocean could also be influencing greater ice growth.
The question remains, however, why these southern winds are getting stronger and, in turn, growing ice at a faster rate. Scientists believe global warming could be at play here, changing the conditions enough to result in an increase in these strong, westerly winds. Others suggest that the ozone depletion in the Southern Hemisphere could be responsible for the stronger blasts, while others simply suggest it’s a matter of natural variability in weather conditions.
Zhang posits that the geographical differences between the north and south poles could also play a significant role in this ice growth. For instance, the sea water in Antarctica is more exposed to wind while the waters of the north are largely protected in a basin from harsh winds.
Despite this recorded growth of sea ice, other researchers still warn the glaciers and ice sheets of Antarctica could be more vulnerable than previously believed.