The amount of sea ice covering the Arctic Ocean was at its second lowest recorded level last month, according to satellite data from NASA and the National Snow and Ice Data Center. The average ice extent this September was 4.61 million square kilometers, which was 2.43 million square kilometers below the 1979-2000 average.
Sea ice, which is frozen seawater between one and four meters thick, expands in the winter and melts in the summer, due to the position of the sun in the sky varying with the seasons. Due to this cycle, the minimum amount of sea ice is always in September. The lowest recorded amount of sea ice was in September 2007.
The extent of sea ice decline was, on Sept. 9 this year, at 4.33 million square kilometers. This, as well as the monthly average, was the second lowest recorded daily sea ice extent. This data is part of a long-term trend that has occurred over the past 30-40 years. Sea ice has been declining by about 12 percent since 1979.
"The decline over the last 30 or 40 years of Arctic sea ice is particularly apparent in minimum sea ice extent in September," Earth and Planetary Science professor Thomas W.N. Haine said. "People wait every year for that."
The loss of sea ice will greatly exacerbate the global warming that is already occurring. Ice is white, which means that it has a very high albedo, or reflectiveness. When the Arctic Ocean is covered in sea ice, it is able to reflect the incoming sunlight, which keeps the Arctic cold.
If this ice is decreased, it is replaced by the ocean, which will absorb the sunlight as it has a low albedo. This results in a positive feedback loop, where the sunlight is absorbed by the ocean, which warms the ocean and melts more sea ice. The diminished sea ice then results in a lower albedo, where more sunlight is absorbed, and the Arctic continues to warm.
"This makes the existence of Arctic sea ice somewhat unstable," Haine said.
According to the Intergovernmental Panel on Climate Change (IPCC), which has various models detailing global warming in the future, the Arctic warms faster than the global average. This effect is called Arctic amplification.
"Global warming is not the same everywhere, in the Arctic it's about twice the global average," Haine said. "The Arctic is a place which is very sensitive to climate change and relatively rapid changes in the environment can occur in the Arctic, more rapidly than, for example, in the middle latitudes."
Because of this rapid warming, the rate at which sea ice disappears will continue to increase, especially if people do not take steps to combat global warming.
"We're in an era of global warming, there's no question about that," Haine said. "It seems that the global warming is going to continue throughout the 21st century [and] it depends on what people do [about] emissions of carbon dioxide."
It is very hard to predict exactly what will happen to sea ice in the future, though, eventually, summertime sea ice will disappear entirely.
"The Arctic will essentially be open water in the summer...and there will probably be patches of floating [sea] ice, which is very thick, in the summer," Haine said. "Eventually, the [summer] Arctic sea ice will go. The IPCC models predict that this will happen over a range of time scales, somewhere [in] the middle of the century, between 2030 and 2060."
However, due to the uncertainty about how fast the sea ice will decline, there is a chance that there will be no more summer sea ice as soon as five years from now.
"There is quite a lot of good evidence to suggest that [the IPCC prediction] is an overestimate on how long it will take for Arctic sea ice to go, so people who study the Arctic specifically rather than the whole global climate system may forecast a [sooner] loss of sea ice," Haine said. "Maybe in the next five to six years...summer Arctic sea ice will go. Nobody knows for sure, but I've heard people say that by 2016, it will have essentially gone."
