Setting a new record is usually an exciting event—but in this case, a record-setting year in the Arctic spells worrisome news.
By June 2012, Arctic sea ice had already melted to its lowest extent for the month since satellite record keeping began in 1979, according to the National Snow and Ice Data Center.
Jupiterimages / Getty Images
How does this affect our weather in the short term and climate in the long term?
It affects weather and climate in several ways, says Andrew Carleton, a Penn State professor of physical geography who specializes in studying sea ice and climate change.
Sea ice has a bright surface, explains Carleton. When it is also covered in snow, up to 90 percent of the sunlight that strikes it is reflected back into space. “This means that only around ten percent of the incident sunlight can be absorbed by the snow and ice, which helps keep it cold,” he notes. “When such a large amount of sea ice melts, it exposes more of the ocean’s surface, which now absorbs up to 90 percent of the sunlight.” This increase in absorption of solar radiation causes the ocean to warm, and further limits how much ice will form the following year and how thick it will become.
The evaporation of moisture from the now-warmer ocean increases cloud formation, Carleton says, and also results in a release of energy as latent heat into the atmosphere, which further warms it. “One result,” he adds, “could be a change in dominant cloud type to more cumulus clouds, and possibly also, more intermittent yet more intense precipitation in the form of rain and snow showers in the Arctic.”
In the middle latitudes—where most people live—the changes in sea ice cover and its reduced thickness can result in greater fluctuations in the weather during the winter, and also larger year-to-year variations, explains Carleton. “For example, the warming of the Arctic atmosphere can enhance blocking high pressure systems in the Greenland-Iceland area during winter and spring,” he notes. “On either side of a blocking high, a cold trough of low pressure usually amplifies in eastern North America and also over Europe, leading to more unusually cold and snowy conditions in those places, such as we had during the winter of 2010-11.”
These seasonal and year-to-year anomalies are expressed in the North Atlantic Oscillation (NAO) and Arctic Oscillation (AO) pressure patterns. At other times, the reduced sea ice in the Arctic may be partly responsible for warmer and drier conditions in middle latitudes (e.g., the winter and spring of 2012) as the atmospheric wave pattern adjusts in the opposite configuration. Says Carleton, “We may see these swings between phases of the NAO and AO become more pronounced, causing greater fluctuations and more unusual weather events in the middle latitudes.”
A warmer ocean also means a warmer atmosphere, even during the colder time of the year, he adds. “The reason for this is the so-called snow/ice-albedo feedback.”
“The ocean—like all water—has a high specific heat, which means that it loses heat only slowly. Arctic-region temperatures can stay warmer through the winter as the ocean gradually gives up that extra heat. Also, because the ocean is warmer than it was when there was a more complete ice cover in summer, it is now more difficult to form new sea ice in the fall and winter seasons; the ice that does form is thinner, so some ocean heat can still pass through it into the atmosphere.”
When the next summer season comes around, the thinner ice and its reduced coverage mean that the ice is easier still to break up by the wind and waves and to melt, again increasing the ocean’s absorption of sunlight.
If the situation does not reverse itself, Carleton notes, the Arctic Ocean could be ice-free in summer by 2030, if not before. And that’s a record-breaker we should be trying to avoid.
Andrew M. Carleton, Ph.D., is a professor of physical geography in the College of Earth and Mineral Sciences. He can be reached at email@example.com.