365 Days of Climate Awareness 187 – Snow Cover

Variations in snow cover largely occur in the northern hemisphere, since Antarctica is always covered with snow and the surrounding southern hemisphere territories which receive seasonal snow are comparatively small, and generally at high elevation. Continental snowfall, and its annual variations, are tracked in North America, Greenland and Eurasia.

February (annual maximum) sea ice extent, northern hemisphere.

Overall the trend of recent decades has been toward less snow cover, especially when factoring in sea ice (which is generally covered with snow). NOAA and National Snow & Ice Data Center (NSIDC) snow cover charts track land snow cover. Adding in sea ice extent is worthwhile in gaining a broader, more holistic understanding of regional dynamics, but the conditions for the formation of sea ice are not at all identical to those for snowfall. Analytically the two are, and should be, considered separately, but combined they make the climatic trend even clearer.

February (annual maximum) snow cover, northern hemisphere. 

There is some variation occurring within the course of the year, as well. Typically maximum sea ice and snow cover extent occur in February, as illustrated. In recent years it has been observed that late fall snow cover has increased, even as the February maximum has shrunk. This points not to overall cooling, but changing seasonal dynamics.

October snow cover, 1967 — 2021. The trend is upward but October is not the maximum snow extent (February is).  This trend has been used by bad-faith commentators in recent years.

In the northwest and southeastern US, snowfall has decreased markedly, while it has increased in the Midwest. It is very possible this is related to the increasing prevalence of polar vortex events, where typically, Alaska and the western portions of Canada and the United States are anomalously warm, while the polar jet stream bends around that region and dips far to the south toward Texas. 

Percentage annual change in snowfall, 1930 - 2007.

As the planet warms, and the polar vortex loses stability, these very cold events in the Midwest are likely to become more common.  In one limited respect recent precipitation trends bear this out. Though overall snowfall is reduced throughout most of the US, in the Midwest, snow is an increasingly large share of total precipitation.

Percentage annual change of snowfall as a total percentage of precipitation, 1930 — 2007.

Tomorrow: glacial ice loss.

Be brave, and be well.