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State of the Poles – 4/7/10

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The state of polar sea ice in March 2010 is fairly good compared to climatological conditions (1979-2000), which strongly contrasts with the past few months when global conditions were below climatology.  As it has done this time of year for a few years in a row, the global sea ice extent increased to the point where it is near climatological values, as this graph demonstrates.  The anomalies observed in 2006 and 2007 become more obvious each time the globe’s sea ice increases in March.  The most recent data show that global sea ice covers ~15.25 million sq. km., compared to 15.75 million sq. km. normally.

Arctic Ice

The state of Arctic sea ice in March 2010 improved significantly from February’s below average conditions.  Favorable weather conditions set up over the Barents and Bering Seas that helped new ice form along the edges of the ice pack present one month ago.  Until the first few days of March, the areal extent of Arctic sea ice was below -2 standard deviations since late June 2009.  Recent conditions have continued a late cool season surge in sea ice areal extent – culminating in the latest date of the year for the maximum extent to be observed: Mar 31st.  It is worth noting that this new ice is very young – ice less than one year old will be the most vulnerable to melting in the next six months.  Older ice is more able to withstand the warmer temperatures.  This rather obvious characterization will be important when discussing the likely outcome of the upcoming melt season.

During March, the Arctic Oscillation was became less intense.  The near-surface temperatures in the Arctic region remained slightly above normal throughout the month, however.  A side note here – above normal temperatures doesn’t mean above freezing.  A couple of prominent climate change deniers idiotically tried to argue in the past month that the warmer than normal temperatures must mean the Arctic was in full melt mode.   So outside of the Bering and Barents Sea regions, less ice volume formed than would have been the case if temperatures were cooler.

The average ice extent for March 2010 was 15.1 million sq. km., the sixth lowest since 1978, when satellite records began. That extent was 670,000 sq. km. more than the record low extent set in 2006.  It was also a substantial improvement over the February difference of 220,000 sq. km.  Since 1978, the Arctic sea ice extent in March has decreased at 2.6% per decade.

Antarctic Ice

The state of Antarctic sea ice in March 2010 is slightly below average relative to climatological norms.  After a pretty normal February, weather conditions conspired to slow down ice growth in the middle of March.  As a result, the areal extent shifted from above normal to almost -2 standard deviations below normal before recovering at the end of the month to be just below normal.  The yearly minimum was reached in early February, growing more or less continually ever since.

Ice Thickness

The last item discussed in the NSIDC report is ice thickness.  As I stated above, the relative thickness of sea ice is one determining factor into predicting the areal extent of ice in a melt season.  The NSIDC report includes plots of different kinds of ice (1st-year, 2nd-year, multi-year), their location at different points in the past year and a time series of the three types.  What is important to take away from the last plot is the increasing prevalence of ice that is less than one year old.  Back in the 1980s, this ice constituted ~55% of the Arctic ice.  In the past decade, that number has increased to 70% of the ice.  2 year and older ice used to make up 30-40% of Arctic ice.  In the past 10 years, that has decreased to 20% and a significant drop-off from that value can be see after 2007 – down to 10% or so in the past couple of years.

Ice that is older is also typically thicker.  The reasons are obvious: it has more time to add ice vertically instead of horizontally.  Snow can fall on it year after year, maintaining the ice’s overall integrity.  In recent years, that kind of ice has nearly disappeared from the Arctic Ocean.  That is important because ice and snow reflect more sunlight back into space than does dark ocean water.  As more areas lose their reflective ice covering, they absorb more sunlight and thus warm up more than normal.  A warmer Arctic Ocean means ice has a harder time forming even when the sun slips below the horizon for the winter.  All that heat has to be moved out of the Arctic into the Atlantic or released back into the atmosphere.  Those processes take time,  which means the next year’s ice has a harder time forming and staying around long enough to thicken so that it survives the following melt season.

Climate scientists fear that the Arctic Ocean could eventually warm up enough so that all the ice melts every summer.  New ice will still form in the winter, but it won’t last longer than a year or two.  Opening up that much area to the sun means a lot more energy that used to be reflected back into space will instead be kept inside our climate system.  Warming the Arctic would have severe consequences on nearby land-based ice – it would melt even faster than it is today.  If land-based ice (on Greenland, for example) melts, it raises sea-levels, among other effects.

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Here are my State of Polar Ice posts from March and January.

Pictures and Graphs

Here is a satellite representation of Arctic sea ice conditions from April 4th (they haven’t been updated since then):

For comparison purposes, here is the similar picture from August:

Here is the time series graph of Arctic sea ice extent with the +/- 2 standard deviations as a light-gray envelope around the climatological average through yesterday:

You can find the NSIDC’s March report here. The page is dynamic, so if you’re reading this after April 2010, that month’s report will show up first. If that’s the case, you can look for the March report on the top pull-down tab on the right-hand side of the page.

Here is a satellite representation of Antarctic sea ice conditions from yesterday:

Here is the time series graph of Antarctic sea ice extent with the +/- 2 standard deviations through yesterday:

Cross-posted at SquareState.

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2 thoughts on “State of the Poles – 4/7/10

  1. Pingback: State of the Poles – 5/5/10 « Weatherdem’s Weblog

  2. Pingback: State of the Poles – 6/21/10 « Weatherdem’s Weblog

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