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Despite Warm Weather, Arctic Sea Ice Extent Near Normal for April

May 10, 2010; 9:47 AM ET

Despite a continuation of unseasonably warm temperatures across a large portion of the far northern latitudes, Arctic sea ice extent was near normal for most of April. According to the National Snow and Ice Data Center. (NSIDC).

April temperatures were about 3 to 4 degrees Celsius (5 to 7 degrees Fahrenheit) above average across much of the Arctic Ocean, and up to 10 degrees Celsius (18 degrees Fahrenheit) above normal in northern Canada!

The main reason for the near-normal ice extent was the unusually late start to the melt season on March 31st, which is almost a month later than normal. The late start was due to the expansion in the southernmost Bering Sea, Barents Sea, and Sea of Okhotsk. These areas remained cool, with northeasterly and northwesterly winds, keeping the overall ice extent close to the average for the month of April.

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Update

Here is the latest chart of the Arctic sea ice extent through early May, and as you can see, there has been a recent downward acceleration. It will be interesting to track this through the summer. Image courtesy of the NSIDC.

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The Polar Research Group from the University of Illinois at Urbana-Champaign also keeps track of the sea ice area in both the northern and southern hemisphere.

As you can see below, the annual sea ice area anomaly in the northern hemisphere since 1979 shows a clear, long-term, downward trend. If you just look at the last 3 years, it has leveled off. We will have to wait and see if this leveling off will continue or is it just some noise in the overall trend.

If we look at the southern hemisphere, there has been a slight upward trend since 1979. Image courtesy of the Cryosphere Today.

The increase in Antarctic sea ice extent is not surprising to climate scientists. When scientists refer to global warming, they don't mean warming will occur everywhere on the planet at the same rate. In some places, temporary cooling may even occur. Antarctica is an example of regional cooling. Even our earliest climate models projected that Antarctica would be much slower in responding to rising greenhouse gas concentrations than the Arctic. In large part, this reflects the nature of the ocean structure in Antarctica, in which water warmed at the surface quickly mixes downward, making it harder to melt ice. (excerpt from the NSIDC).

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What is the difference between sea ice area and extent? (from the NSIDC site)

Area and extent are different measures and give scientists slightly different information. Some organizations, including Cryosphere Today, report ice area; NSIDC primarily reports ice extent. Extent is always a larger number than area, and there are pros and cons associated with each method.

A simplified way to think of extent versus area is to imagine a slice of swiss cheese. Extent would be a measure of the edges of the slice of cheese and all of the space inside it. Area would be the measure of where there is cheese only, not including the holes. That is why if you compare extent and area in the same time period, extent is always bigger. A more precise explanation of extent versus area gets more complicated.

The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or AccuWeather.com

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