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Along with this past winter being the warmest on record for the globe, it now appears as though it has set another new record

It's Official! 2015 Arctic sea ice maximum reaches lowest extent on record

Scott Sutherland
Meteorologist/Science Writer

Tuesday, March 24, 2015, 08:40 GMT - Along with this past winter being the warmest on record for the globe, it now appears as though it has set another new record.

According to the U.S. National Snow and Ice Data Center, as of 25 February, Arctic sea ice reached its maximum extent for the year, growing from a seasonal low in 2014 of 5.03 million square kilometres (around 1.95 million square miles), up to a seasonal max of 14.536 million sq kms (5.6 million square miles). Based on over three decades of observations, that is the smallest maximum sea ice extent ever recorded.

This extent also nearly broke a record for earliest maximum ever. The average date of maximum sea ice extent in the Arctic - from the years 1981-2010 - is March 12, over two weeks after this was reached. The current record for earliest maximum is held by 1996, when Arctic sea ice reached its seasonal maximum extent on Feb 24. At the same time, though, there was nearly 900,000 square kilometres more ice in the north in 1996 than in 2015 (15.426 million sq kms in 1996 vs 14.536 million sq kms 2015).

Although sea ice extent leveled off after the downturn on Feb 25, and it's possible that there may be some growth going forward, the NSIDC said that "it now appears unlikely that there could be sufficient growth to surpass the extent reached on February 25."

Maximum Arctic sea ice extents since 2010, which include some of the lowest on record, and now 2015, which is now the lowest on record. Credit: NSIDC

Will this record low maximum extent, combined with one of the earliest maximums we've seen, mean a new record low for minimum extent towards the end of summer as well?

It's certainly not a great start for the year, but a record low maximum does not necessarily mean a new record low minimum.

"Scientifically, the yearly maximum extent is not as interesting as the minimum. It is highly influenced by weather and we’re looking at the loss of thin, seasonal ice that is going to melt anyway in the summer and won’t become part of the permanent ice cover," Walt Meier, a sea ice scientist at NASA’s Goddard Space Flight Center, said in a statement. "With the summertime minimum, when the extent decreases, it's because we're losing the thick ice component, and that is a better indicator of rising temperatures."

"The winter maximum gives you a head start, but the minimum is so much more dependent on what happens in the summer that it seems to wash out anything that happens in the winter," Meier added. "If the summer is cool, the melt rate will slow down. And the opposite is true, too: even if you start from a fairly high point, warm summer conditions make ice melt fast. This was highlighted by 2012, when we had one of the later maximums on record and extent was near-normal early in the melt season, but still, the 2012 minimum was by far the lowest minimum we've seen."

So, exactly what the yearly minimum ice extent will look like - which we typically see in mid-to-late September - will depend on exactly what the the weather will be like, and how the current weak El Nino in the Pacific influences that weather.

What's happening in the south?

Although Arctic and Antarctic sea ice are influenced by different geographical factors (Arctic ice being constrained by land and Antarctic ice being free to expand through mostly open water), it's still worth mentioning that while Arctic sea ice was reaching this record low maximum, Antarctic sea ice reached its fourth highest summer minimum on record (2003, 2008 and 2013 had higher minimum extents).

However, rather than indicating some kind of balance, higher than average Antarctic sea ice extents are generally thought to be due to two factors:

  1. Near-freezing fresh water flowing off melting coastal glaciers (mainly due to warmer sub-surface ocean layers), collecting in a poorly-mixed surface layer and refreezing due to frigid winds, and

  2. Stronger westerly winds blowing more strongly on sea ice, causing it to circulate faster and thus - by the action of the Coriolis effect - move farther away from the Antarctic coastline.

According to the NSIDC, the small increases seen in the Antarctic are not outside of the natural variability expected for the region, based on climate models, and extents there should decrease as global warming continues. Meanwhile, "for the past few years, Arctic sea ice extent for most months has been more than two standard deviations below the 1981 to 2010 mean, particularly in summer."

Source: National Snow and Ice Data Center | NASA | NSIDC

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