A story on 16 Dec 2016 from the NASA Earth Observatory site said the Antarctic and Arctic sea ice amounts for November 2016 were both at record lows for that month. The Arctic is in the process of refreezing the surface sea ice as it goes into the winter months. The Antarctic is in the process of melting the sea ice as it goes into the summer months. A chart from the story shows the total amount of sea ice north and south from 1 Jan 1979 to 14 Dec 2016. There has been gradual decline in the total. For 2016, the total is significantly less for the last months of the year. An animated version of this chart is in the linked article.
Sea ice forms from water already in the oceans. Changes to the total does not alter sea level. Melting of land based ice drains into the oceans and does raise sea level. The decrease in total sea ice is due to shifting winds and warmer temperatures of the water. The underlying reasons and prognosis for future effects is an area of intense scientific study.
South Polar Sea Ice
How much does the Antarctic sea ice extent vary between March and September when it is at minimum and then maximum? These charts from the National Snow and Ice Data Center show the extents for 1979 and then 2016. The pink line boundaries are 30 year medians between 1981-2010. Comparing across, there is a great seasonal variation. Comparing down, the change in the extents between 1979 and 2016 appears small. Actually, the extent has grown a small amount annually according to the NSIDC.
North Polar Sea Ice
How much does the Arctic sea ice extent vary between March and September when it is at maximum and then minimum? Again, let’s compare the NSIDC charts for 1979 and then 2016. Comparing across, there is great seasonal variation. But, there is a large change in extent between 1979 and 2016, especially evident in the two charts for September on the right. The extent for Sep 2012 set a record for the minimum. The famed Northwest Passage off the coast of Canada is becoming a reality.
Trends in Extent of Sea Ice
The total extent of sea ice is plotted monthly for both polar regions. First, we look at the Antarctic values and trend line. It shows the variations month to month with a slight increasing trend of about 1.2% per decade since 1979. The large drop at the end is of concern. Does it indicate a major trend change? We don’t know.
The Arctic region shows a pronounced and steady decline in extent of sea ice of 3.4% per decade. That is three times the increase in the Antarctic rate. The total extent of each is not much different at 11.3 and 13.1 million sq km.
As noted in the chart at the top of this post, long-term records show a global decline in total sea ice. The increases in Antarctic sea ice have not offset the losses in the Arctic. Climate change is leading to warming of the atmosphere and the oceans. These in turn alter circulation patterns of the atmosphere and the ocean currents. Previous posts about Polar Ice can be found here.
Global land and ocean temperatures have deviated from the 20th century average by increasing amounts since 1980. The year 2016 is the third consecutive year a record has been set.