The extent of Arctic sea ice is an important marker for global climate change. In the last forty years it also has been unequivocally shrinking. NASA has been tracking Arctic sea ice extent at different times of the year, with the September minimum being an important point of comparison. Like any chaotic system there are going to be short term fluctuations, but the long term trend is crystal clear. Look at the graph and look at the video on the NASA site linked above – the shrinking is clear.

The first estimates for September 2017 are in and they are consistent with the overall trend. Arctic sea ice’s most recent maximum for the September minimum was in 1996 at 7.87 million square km. The minimum minimum was in 2012 at 3.62 million sq km – less than half. This year the minimum is estimated to be 4.7 million sq km, slightly more than 2016. All of the last 10 years are below the average for the previous 30 years.

This past year we had a warm winter, which led to the lowest amount of March Arctic sea ice on record, but a cool summer allowed the Arctic ice to rebound a bit.

All of this adds to the strong scientific consensus that the globe is warming and this trend is largely due to human factors (not natural cycles). But as you probably know, there is a well-financed campaign of denial, ideologically and financially motivated, to muddy the waters and create doubt and confusion about this scientific consensus. This is easy to do with complex scientific questions.

Continue Reading »

Patrick Burkhart and his colleagues recently published a review of their research on the cryosphere, which is a collective term for all the ice on the surface of the Earth. In addition to their review of the science, the new information they add is a photographic project documenting the retreat of glaciers around the globe.

The retreat of the cryosphere is one of the many lines of evidence supporting the idea that the earth has been warming over the last half-century. There are several different ways to look at this. You can look at each pole to see the extent of ice coverage at their peak in winter and minimum in summer. You can look at specific ice sheets, like Greenland. You can look at glaciers. And you can look at total global ice, the cryosphere, which of course is the best single measure.

With regard to glaciers, the authors point out that there are many variables affecting the current size of any individual glacier. It is possible but difficult to account for all these variables and isolate one as a primary cause of melting. However, you can survey glaciers from around the world, which is a good way to control for local variables. When we do this we find there is a significant trend toward glacial retreat.

Continue Reading »