Climate Change, Global Warming, and Agricultural Droughts - Monitoring and Predicting Agricultural Drought: A Global Study - page 433

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orological Organization (WMO; chapter 31) and the United Nations En-
vironment Program (UNEP) set up the Intergovernmental Panel on Cli-
mate Change (IPCC) in 1988. The IPCC attempted to establish a consensus
among the results of calculations from 20-30 different climate models. The
IPCC has, over a decade, become more confident about the importance of
the role of human activity vis-à-vis the natural variations in the climate.
It also warns, however, that regional or local changes may not necessarily
all be in the same direction as the general trend. The IPCC's main conclu-
sions can be summarized (Houghton et al., 2001; McCarthy et al., 2001)
as follows:

1. Global mean near-surface air temperature increased by about
0.6°C over the 20th century.
2. Temperatures in the lowest 8 km of the atmosphere have risen
during 1960-2000 at about 0.1°C per decade.
3. Snow cover and ice extent have decreased.
4. Global mean sea level has risen and ocean heat content has
increased.
5. There have been changes in precipitation, with increases in
some areas but decreases in some other areas.
6. Most of the warming observed over the last 50 years is at-
tributable to human activities; any contribution from natural
factors is small.
7. Concentrations of atmospheric greenhouse gases, including tro-
pospheric ozone, have continued to increase as a result of hu-
man activities.
8. Stratospheric ozone depletion and anthropogenic aerosols have
a cooling effect, or negative greenhouse effect.
9. Human influences are expected to change the atmospheric com-
position throughout the 21st century.
10. Projected changes in atmospheric composition arising from hu-
man activities, based on various assumptions, will lead to fur-
ther anticipated temperature and sea level rises throughout the
21st century.
11. There is likely to be an increase in various extreme events.

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C limate Change and Agriculture
Temperature and rainfall are the key factors in making decisions about
what crops to grow. Thus, agriculture will need to adapt to changes in
climate. In nondesert areas droughts arise as fluctuations within the local
weather pattern. They cannot be prevented or eliminated, but making use
of climate models to obtain reliable predictions of their expected frequency
of occurrence can contribute toward wise planning of agriculture to mini-
mize drought losses.
It is useful to consider the global estimates of the area that potentially
can be endangered by drought. If from the total global land area we elimi-