It is true that the Bering Sea reached a record high extent during the month of April. Much has been made about this record by some bloggers but not much attention has been paid to the other side of the world, where ice extents have been well below normal.
Let’s break down the data a little bit and explore just how Arctic ice extent is faring compared to recent years and what it means.
The MASIE website is a terrific tool for breaking down Arctic sea ice. In addition to hosting the total Arctic ice extent in CSV (Microsoft Excel) format, it also divides the Arctic into 16 individual seas in numerical and time series format.
The time series format is extremely useful as it allows us to view the current trend and compare it to recent years. MASIE gets its data from the National Ice Center’s IMS product, which is a map of snow and ice cover across the Northern Hemisphere produced daily based on satellite data products. The high resolution of the MASIE ice extent (4km) and the ingestion of multiple data sources improves upon the ice monitoring of the traditional microwave products.
You may recall this winter/spring that while the East Coast, Midwest and Great Lakes basked in record warmth, Alaska endured a brutally cold and snowy winter, breaking many records. This record cold coupled with a northerly wind pattern helped to grow and expand the ice pack in the Bering Sea to those record levels.
So, does this mean that long-term decline in Bering Arctic sea ice is over? Not quite. In addition to the fact it’s now melting at a rapid clip, all the ice in the Bering Sea is made up of what’s known as first-year ice which melts out completely every year during the summer. This means that at some point this summer, it will once again reach its long-term average: zero.
In short, winter Bering Sea ice has no bearing on the sea ice minimum when it is reached later in September as it will be completely ice free long before. An above normal winter extent may delay or slow down slightly some of the melt in the neighboring Beaufort/Chukchi Seas but with Bering Sea ice now quickly on the decline, it’s likely to have minimal impact.
Furthermore, even with the Bering sea’s elevated ice extent, the European Arctic has experienced much below normal levels. In the Barents and Kara Seas, ice extents have been running below even the already depressed levels of recent years. (Winter conditions there were much warmer than normal.)
This region of the European Arctic has more of an impact on the Arctic as a whole since the ice doesn not melt out completely every year as in the Bering region. It als contains thicker, multi-year ice which is more of an indicator of Arctic sea-ice “health”.
Via Climate Central: A NASA video showing one important effect of the waxing and waning of the seasons. It shows satellite views of Earth over both the North and South Poles, side-by-side, demonstrating how sea ice expands in summer and melts back in winter, see-sawing from one pole to the other as summer and winter alternate.
Sea ice that survives the summer’s melt and has a chance to grow again the following winter is classified as “second-year ice” and any ice which has survived more than one summer’s melt is called “multi-year ice”. These ice types are much thicker and harder than first year ice and are typically found in the high Arctic regions. Much of these thicker ice types have been lost in recent years, making the icepack as a whole more vulnerable to melt.
Areas like the Barents and Kara Seas are areas where first year ice has a chance to survive the melt season and create new areas of this thicker ice. But, with ice running below normal, these areas themselves are more vulnerable to melting, making multi-year ice generation, and replenishment of the Arctic ice cap, even harder.
While high relative to recent years, NOAA notes April 2012 was “the 13th consecutive April and the 131st consecutive month with below-average Arctic ice extent”. The long-term trend in April sea extent is a decrease of 2.4 percent per decade.
Considering everything together, the Arctic ice extent has made a nice recovery this year, nearly reaching its long-term average for the first time in recent years. “Average”, however, can be a tricky term to use. Region by region, ice cover varies greatly at present with opposing sides of the Arctic seeing very different trends in sea ice extent.
It’s also important to note there is considerable year-to-year variability in Arctic sea ice, so levels in any given year don’t necessarily provide insight into the long-term trend (which is decidedly downward).
Finally, sea ice extent is merely a one-dimensional measure of Arctic ice. A more holistic indicator, sea ice volume - which is estimated each month at the University of Washington (UW)- shows levels well below normal. UW reports:
Ice volume for March 2012 was 20,800 km3 the same as last year but 35% lower than the maximum in 1979, 24% below the mean and 1.7 standard deviations from the trend.
The low volume speaks to the importance of the multi-year ice which has been chipped away at over the long-term.
What lies ahead for Arctic ice? The National Snow and Ice Data Center provides this insight:
While ice conditions approached the 1979 to 2000 average levels for this time of year, the high ice extent will have little influence on how much ice melts this summer. Much of the ice cover is recently formed thin ice that will melt out quickly. Research has shown that sea ice extent in spring does not tell us much about ice extent the following summer. More important to the summer melt is the thickness of the ice cover, and summer weather.