A New Low for Arctic Sea Ice
There has been a lot of important climate news in recent weeks and months. In addition to record warmth, an unusually active Atlantic hurricane season, and a devastating string of extreme weather events in the U.S. and around the world, Arctic sea ice has reached a new low in its total volume.
The ice covering the Arctic Ocean goes through a seasonal cycle in which it expands during the winter, reaching its maximum extent in March, and shrinks during the summer, reaching its minimum extent in September. Satellites have been observing the daily coverage of sea ice since 1979, during which time the summer minimum has declined rapidly over the decades. In 2007, the summer minimum dropped by a startling amount compared to previous summers, generating an iconic graph that was splashed across blogs and newspapers around the world (Figure 1). This record still holds, although every year since 2007 has seen below-average summer minima.
According to the National Snow and Ice Data Center (NSIDC), Arctic sea ice reached its minimum extent for 2010 on September 19 at 1.78 million square miles. Although this was the third-lowest extent behind 2007 and 2008, the sea ice set a new and probably more important record by reaching the lowest estimated volume – or total amount of sea ice – since satellite observations began in 1979.
Picturing an ice cube floating in a glass of water is a good comparison. The ice cube has three dimensions. But looking directly down at the glass, you see only the two dimensions that cover part of the surface of the water. When you look at the glass from the side, you can also see that the ice cube has depth, and that most of the ice is below the surface. The same phenomenon holds for sea ice, so if the ice melts from below, it becomes thinner and its total volume decreases.
This year, even though the area of the ocean’s surface covered by ice was a little larger than in 2007, the ice was much thinner, making its total volume much less than in 2007 or any previous year since estimates began in 1979 (Figure 2).
The rapid decline in total ice volume is significant since it takes less heat to melt a small volume of ice than to melt a larger volume. The area of ice cover can recover in one season, as it did in 2009, but the thickness builds up over several years. Consequently, the low volume of ice currently in the Arctic is more susceptible to melting next summer and the summer after that than was the 2007 ice. Consequently, scientists are wondering whether the Arctic could become ice free during the summer much sooner than previously projected.
The opening of the Arctic has enormous implications, ranging from global climate disruption to national security issues to dramatic ecological changes. The Arctic may seem far removed from our daily lives, but changes there are likely to have serious global implications.
- An ice-free Arctic Ocean will absorb more sunlight and convert it to heat, thus amplifying warming.
- The Arctic currently removes CO2 from the atmosphere, but physical and biological changes in the Arctic could cause it to switch to releasing CO2 and CH4 (a very potent greenhouse gas) to the atmosphere, thus amplifying global warming.
- Atmospheric circulation and therefore precipitation and storm patterns may be altered by a warming Arctic and changes in how the ocean interacts with the atmosphere in the region.
- A warmer, ice-free Arctic Ocean with more freshwater from snow and ice melt could change global ocean circulation patterns, thus altering marine ecosystems (i.e. fisheries) around the world and changing patterns of precipitation and storms on a very broad scale.
- More rapid melting of ice on land will accelerate sea level rise and could destabilizing the Greenland Ice Sheet, leading to abrupt and massive sea level rise.
- Countries have begun to compete for access to untapped natural resources in the Arctic. Unlike other international arenas, such as Antarctica, coastal waterways, and space, there are no agreed international rules to govern how different countries will access and utilize the Arctic.
Jay Gulledge is Senior Scientist and Director of the Science and Impacts Program