Geoscience Reference
In-Depth Information
3
1.0
Correlation coefficient, r = -0.61
2
0.5
1
Figure 13.24
Time series of annual snow
extent and land surface temperature
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) is 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-
2000. Temperature calculations are based
on the Jones datasets; anomalies are with
respect to the period 1960-1990.
Source: D. Robinson, Rutgers University, and A.
Bamzai (NOAA/.OGP).
0
0.0
-1
-0.5
-2
Snow anomalies
Temperature anomalies
Snow anomalies 5-year weighted mean
Temperature anomalies 5-year weighted mean
-1.0
-3
1970
1975
1980
1985
1990
1995
2000
Dry lands are expected to be profoundly
affected by climatic change. Dry rangelands
(including grasslands, shrublands, savannas, hot
and cold deserts) occupy 45 percent of the
terrestrial land surface, contain one-third of the
world's total carbon in their biomass, and support
half of the world's livestock and one-sixth of the
world's population. Low-latitude rangelands
are most at risk both because an increase in
CO
2
(increasing the carbon/nitrogen ratio) will
decrease the nutrient value of forage and because
the increasing frequency of extreme events will
cause environmental degradation. Most deserts
are likely to become hotter but not significantly
wetter. Any increases in rainfall will tend to
be associated with increased storm intensity.
Greater wind speeds and evaporation may be
expected to increase wind erosion, capillary rise
and salinization of soils. Central Australia is one
of the few places where desert conditions may
improve.
A major consequence of global warming will be
that desiccation and soil erosion will increase in
semi-arid regions, rangelands and savannas
adjacent to the world's deserts. This will accelerate
the current rate of desertification, which is
proceeding at six million hectares per year partly
due to high rainfall variability and partly to
unsuitable human agricultural activities such as
overgrazing and over-intensive cultivation.
Desertification was estimated to affect nearly 70
percent of the total dry land area in the 1990s.
