Sunday, September 20, 2015

Sea Ice Has Declined by 900,000 Square Miles This Year

The sea ice extent at the north and south poles has undergone a massive decline this year. Antarctic and Arctic sea ice extent have declined by 1.83 million and 550,000 square kilometers, respectively, in the past 365 days. Thus, total sea ice extent has declined by 2.4 million square kilometers (over 900,000 square miles). For perspective, this reduction in area covered by sea ice at the poles is 5 and a half times the size of California.

Antarctic sea ice declined from 20.1 million square kilometers to 18.3 million kilometers on September 20 from 2014 to 2015 according to the National Snow & Ice Data Center. Arctic sea ice declined by from 5.1 million kilometers to 4.5 million square kilometers during this period. (For reference, 1 square kilometer equals 0.386 square miles)

Antarctic Sea Ice Extent
(area of ocean with at least 15% sea ice extent

Click on image to view interactive larger version of this chart (next click on Antarctic button)

Arctic sea ice is in a long term downtrend. This year featured the lowest maximum extent and fourth lowest minimum in recorded history. On the other hand, Antarctic sea ice extent had been increasing from 2011 through 2014. The trend in Antarctic sea ice extent abruptly reversed in July, 2015. In the past year Antarctic sea ice has gone from record extent to a below average extent (average based on 1981-2010).

Arctic Sea Ice Extent
(area of ocean with at least 15% sea ice extent

Click on image to view interactive larger version of this chart

It's probably questionable whether combining Antarctic and Arctic sea ice extent generates a particularly meaningful metric. The warming planet is the primary reason for shrinking Arctic ice, whereas there are complicated counter balancing factors at play in the Antarctic,  The changes in extent between the two poles are not equivalent. The numerous factors influencing Antarctic sea ice extent create interactions that are the subject of ongoing research. Some scientists have speculated the melting land based Antarctic glaciers may produce incremental sea ice, while others are focusing on wind patterns.

It is also suspect to focus on data from a single year, as opposed to multi year trends. Despite these qualifiers, the decline this year should put to bed the idiocy spouted by climate science deniers that global warming is a hoax because sea ice is increasing. The deniers' claim that the decline in Arctic sea ice was compensated for by an increase in Antarctic sea ice was always absurd, and at this point can only be made by cherry picking results from periods that exclude July through September 2015.

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