Why Is Winter Snow Extent Interesting?

Why Is Winter Snow Extent Interesting?

Several people keep asking why am I focused on winter snow extent.  This seems fairly obvious, but I will review here:

1. Snow falls in the winter, in places where it is cold.  Snow does not generally fall in the summer, because it is too warm.

2. Winter snow extent is a good proxy for winter snowfall.  Snow has to fall before it can cover the ground.

So what about summer snow cover?  Summer snow cover declined significantly (from the 1970s ice age scare) during the 1980s, but minimums have not changed much since then.  As you can see in the graph below, the overall annual trend since 1989 has been slightly upwards.

Data from Rutgers University Global Snow Lab

Note in the image above that there has been almost no change in the summer minimum snow extent since 1989, and that the winter maximums have increased significantly as seen below.

Summer snow cover is affected by many factors, but probably the most important one is soot, as Dr. Hansen has stated.

The effects of soot in changing the climate are more than most scientists acknowledge, two US researchers say. In the Proceedings of the National Academy of Sciences, they say reducing atmospheric soot levels could help to slow global warming relatively simply. They believe soot is twice as potent as carbon dioxide, a main greenhouse gas, in raising surface air temperatures. … The researchers are Dr James Hansen and Larissa Nazarenko, both of the Goddard Institute for Space Studies, part of the US space agency Nasa, and Columbia University Earth Institute.

http://news.bbc.co.uk/2/hi/science/nature/3333493.stm

The global warming debate has until now focused almost entirely on carbon dioxide and other greenhouse gas emissions, but scientists at the University of California – Irvine, suggest that a lesser-known problem – dirty snow – could explain the Arctic warming attributed to greenhouse gases….The effect is more conspicuous in Arctic areas, where Zender believes that more than 90 percent of the warming could be attributed to dirty snow.

http://www.scienceagogo.com/news/20070506202633data_trunc_sys.shtml

In summary, winter snowfall is increasing and currently at record levels, and summer snow extent is not changing much.  Earlier changes in summer snow extent were likely due primarily to soot – not CO2.