Observations: Cryosphere Changes

• Northern Hemisphere Snow Cover
• Substantial recent declines in spring cover
• Concentrated in areas near freezing average temperature
• Sea Ice Extent
• Annual average decreases by about 2.5%/decade in Northern Hemisphere, no real change in Southern Hemisphere
• NH decreases most pronounced in summer with trend of 7.5%
• Glaciers and Ice Caps
• Long term records of mountain glaciers show widespread retreat, starting around 1850
• Tropical glaciers disappearing fast
• Greenland ice cap thickening in interior, thinning along the coast
• Trend in mass balance appears to be negative
• Increased accumulation in center more than offset by more rapid movement and melting at the coast
• Antarctic ice sheet shows similar trend, but with more regional variation
• Permafrost
• Permafrost temperatures increasing throughout Northern Hemisphere as much as 2^oC
• Area of seasonally frozen ground shows substantial decrease