Global Outlook for Ice & Snow

Temperature (˚C)

0.5

5 m depth

0

8 m depth

-0.5

-1

-1.5

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

1974 1975 1976 1977

-4

-4.25

-4.5

Seasonal thawing

-4.75

Seasonal freezing

-5

Thickness (m)

Figure 7.9: Permafrost temperatures and active-layer thickness during 1974–1977 and 1990–2004 measured in a borehole at the “Cosmostation” permafrost observatory, 3300 m above sea level, Northern Tien Shan Mountains in Central Asia . Source: Based on Marchenko and others 2007 82

China

35.6 per cent between 1974 and 1996 84 , while the perma- frost area of the northern Qinghai-Tibet highway decreased by 12 per cent between 1975 and 2003 85 . In the Xing’anling Mountains in northeast China, many patches of permafrost have disappeared 86 . The permafrost area in China is project- ed to decrease by 30-50 per cent during the 21st century 79,87 .

Permafrost in China has degraded significantly during the past 40 years 79,83 , with changes observed in both permafrost extent and temperature. The area of the southern Qinghai- Tibet highway with underlying permafrost decreased by

CHAPTER 7

FROZEN GROUND

195