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