Are scientists conservative about sea ice?
Guest post by Walt Meier, NSIDC Scientist
Arctic sea ice set a record minimum extent in September 2012, far below the previous record low in 2007. Summer extents have been far lower than average for the last decade, with several record or near-record years. Looking at the numbers, one is tempted to think that the Arctic Ocean may reach nearly sea ice-free conditions within just a few years. But most expert analyses indicate that we’re likely at least a couple decades away from seeing a blue Arctic Ocean during the summer.So what is going on here? Readers have asked if scientists are being too conservative in their assessment of the recent ice loss. We asked Walt Meier, NSIDC scientist, to address this question. Following is his response.
Conservative science, or complex systems?
Scientists by their nature tend to be conservative when viewing new evidence. While the recent years have been surprising, most scientists are not willing to accept that ice-free conditions are imminent. But that is not because they’re being too conservative. The Arctic sea ice system is complex and there are many aspects that are not yet well understood.
A variety of feedbacks promote ice growth or ice loss. For example, sea ice has a high albedo, meaning it reflects the sun’s energy back into space. Darker ocean water has a low albedo, meaning it absorbs more of the sun’s energy, and thus more heat. As sea ice extent decreases, the change in albedo spurs a well-known feedback that enhances summer melt because the ocean absorbs more of the sun’s energy than the ice.
Likewise, there are also negative feedbacks that will slow the loss of ice. One of these results from the fact that ice grows more rapidly when there is no ice or thin ice than when thick ice is present under the same air temperatures. Thus in fall when the sun goes down and the atmosphere gets cold, open water areas grow ice quickly allowing such regions to “catch up” to thicker ice regions. These feedbacks and many other factors, such as ocean and air temperatures, wind, and weather patterns, prevent an easy assessment of a complex system.
Read the rest here.
Image caption: The U.S. Coast Guard Cutter Healy encountered only small patches of sea ice in the Chukchi Sea when this photograph was taken on July 20, 2011. (Courtesy NASA Goddard Space Flight Center)