Reduced Cold

March and April Northern Hemisphere Snow
Covered Area

Northern Hemisphere March-April snow covered area from station-derived snow cover index before 1972 and from satellites during and after 1972 . Black dots represent data from individual years. Black line shows smoothed trend accounting for variation within a decade.

Trenberth et al. 2007

Increasing hot weather has been accompanied by a decrease in cold weather. Across the globe in recent decades, there has been a reduction in the number of cold extremes, such as very cold nights, and a widespread reduction in the number of frost days in mid-latitude regions.1 In the United States, there have been fewer unusually cold days. The 10-year period ending in 2007 witnessed fewer severe cold snaps than any other 10-year period since record keeping began in 1895.2 These changes cannot be explained by natural variation, and correspond very well with computer simulations that include human influences on climate.3 Snow cover has decreased in most regions, especially in the spring, and mountain snowpack has also decreased in several regions.4

Snow Cover Decreasing Across the Northern Hemisphere

Snow cover has decreased in most regions, especially in the spring, and mountain snowpack has also decreased in several regions.5

Freezes Coming Later and Thawing Earlier

U.S. Frost-Free Season Length

Change in the length of the frost-free season averaged over the United States.

Kunkel 2008

The freeze date for lakes and rivers in the Northern Hemisphere has moved later in the year, at an average rate of six days per 100 years, while the ice break-up date has moved up earlier in the year, at an average rate of a little more than six days over the last 100 years.6 Smaller lakes in North American show a uniform trend toward earlier ice break-up, up to 13 days early.7

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(Full List of References)

References

  1. Gutowski et al. 2008
  2. Gutowski et al. 2008
  3. Stott et al. 2010
  4. Trenberth et al. 2007
  5. Solomon et al. 2007a
  6. Trenberth et al. 2007
  7. Gutowski et al. 2008