Monday, January 22, 2018

History of Sea Ice

The National Snow and Ice Data Center (NSIDC) had a very interesting posting concerning the history of sea ice extent since 1850. This is a rather nice piece of work involving historical records going back 130 years before the start of satellite monitoring. Researchers used "a compilation of maps, ship reports, and other records" to build the record. Then they plotted it and the story it tells is pretty graphic. Take a look:

Source: NSIDC

The extent is color-coded where extent greater than the 1850-2013 baseline is colored in shades of red and extent less than that baseline is colored in shades of blue. The calibration of the colors is displayed on the right-hand axis. The bottom axis is in years beginning in 1850 and going to 2013. The vertical axis is months of the year with January at the top and December at the bottom.

Before the 1970s, we can see the ice extent is displayed almost continuously in shades of red with an occasional block of blue here and there until an extensive blotch of blue extending from 1937 to 1943. The notable thing about that blue blotch is that it does not go into the winter months.

However, beginning in the 1970s we can see the extent becomes increasingly blue. At first, the deficit is limited to the summer months, but by the 1990s it's consistently blue even in the winter. By the 2000s, the graph shows a deficit in extent for all months. There has not been a red-shaded block since the mid-1980s. Recent years show a trend of increasingly darker shades of blue.

This is another graphic in the same article:

Source: NSIDC
In this graphic, they took 50-year periods and plotted the extent of the smallest minimum extent for each period. The periods are marked above each graphic while the specific year is displayed on the upper-left portion of each plot. You can see, even by the 1940s we were already beginning to see evidence of smaller extent. This is certainly clear by the third plot and the devastating 2012 extent is displayed in the last one.

There are a few more graphics, but I wanted to share one last one with you.

Source: NSIDC
These two graphs show the date the Beaufort Sea (top) and Chukchi Sea (bottom) ice-over for the period of 1979 - 2017.  In both cases, we can see these two seas are becoming ice-covered at a later and later date. Notice the data for the Chukchi Sea stops in 2016. That's because this sea did not ice-over before the end of 2017.

By the way, the Arctic sea ice extent is currently trending very close to the record low extent for this time of year.  The conclusion is very clear - Arctic sea ice is going away and will not be coming back.

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