Geoscience Reference
In-Depth Information
Figure 13.25
Time series of annual
snow extent and land-surface temper-
ature anomalies. Annual anomalies
are the sum of monthly anomalies,
area-averaged over the region north
of 20°N, for the snow hydrological
year, October to September. The
snow anomaly (in million km
2
) is on
the left vertical axis, the temperature
anomaly (°C) on the right vertical axis.
Bar plot indicates snow anomalies,
the fine line indicates temperature
anomalies. The correlation coefficient,
r is -0.61. The thick curves are five-
year weighted mean values. Snow
cover calculations are based on the
NOAA/NESDIS snow cover maps for
1967 to 2000. Temperature calcula-
tions are based on the Jones datasets;
anomalies are with respect to the
period 1960 to 1990.
Source
: D. Robinson, Rutgers University,
and A. Bamzai, NOAA/OGP.
causes of such calving are more related to the long
history of the ice shelves and ice dynamics than to recent
climatic trends. However, the disintegration of ice
shelves in the northern Antarctic Peninsula - the Wordie
shelf on the west side in the 1980s and the northern
Larsen shelf on the east side between 1995 and March
2002 - is attributed to regional warming of 2.5°C over
the past fifty years.
Snow cover extent shows the clearest indication of
a response to recent temperature trends. Northern hemi-
sphere snow cover has been mapped by visible satellite
images since 1966. Compared with the 1970s to mid-
1980s, annual snow cover since 1988 has shrunk by
about 10 per cent (Figure 13.25). The decrease is pro-
nounced in spring and is well correlated with springtime
warming. Winter snow extent shows little or no change.
Nevertheless, annual snowfall in North America north
of 55°N increased between 1950 and 1990. Much
work remains to be done to analyse station snowfall and
snow depth records, particularly since these variables
are difficult to measure and the design of gauges and
shields has changed through time. Scenarios for
AD
2050 suggest a shorter snow cover period in North
America, with a decrease of 70 per cent over the Great
