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skill, within time spans ranging from seasons to over one year. The ob-
jectives of CLIVAR are first to describe and understand the physical pro-
cesses responsible for climate variability and predictability on seasonal,
interannual, decadal, and centennial time scales through the collection and
analysis of observations and the development and application of mod-
els of the coupled climate system. The second objective is to extend the
record of climate variability over the time scales of interest through the
assembly of quality-controlled paleoclimatic and instrumental data sets.
A third objective is to understand and predict the response of the cli-
mate system to increases of radiatively active gases and aerosols and to
compare these predictions to the observed climate record to detect the
anthropogenic modification of the natural climate signal. CLIVAR em-
phasizes the following research themes related to drought: (1) establish-
ing the limits of predictability, taking a regional approach and giving
special attention to global ENSO (El Ni no/Southern Oscillation; chapter
3) response areas and monsoon circulation systems; (2) assessing the re-
sults of GCM (Global Circulation Model) coupled model runs to assess
their ability to reproduce the patterns of spatial and temporal variabil-
ity of rainfall; (3) studying drought- and flood-inducing processes; (4) in-
vestigating the predictive capability of SST (sea-surface temperature) and
ocean-atmosphere coupling processes in the tropical Atlantic and Indian
Oceans using the proposed observational arrays; (5) improving the un-
derstanding of tropical mid-latitude interactions and their impacts on pre-
dictability for northern and southern Africa; (6) investigating land-sea-
air interaction processes using remote and in situ observations and con-
ducting numerical modeling experiments to establish feedback processes;
and (7) developing innovative, low-cost solutions to land-based observa-
tional and communication needs and to the construction of data bases,
identifying centers of existing expertise, and developing assistance pro-
grams and projects to ensure the potential for a local base of ongoing
research.
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lobal Climate Change and Dryland Climate
Many scientists and policy-makers believe that climate changes in drylands
over the next century will be driven in part by the continued build-up of
anthropogenic greenhouse gases. Increases in the global atmospheric con-
centration of carbon dioxide, methane, nitrous oxides, various halocarbons
and other greenhouse gases are well documented, and the upward trends
for many of these trace gas concentrations are expected to continue well
into the next century. Concern about climate has reached communities in
all parts of the globe. As communities have adapted to their local climate,
they are sensitive to its variations, and many are threatened by climate
change.
The WMO/UNEP Intergovernmental Panel on Climate Change (IPCC)
assessments have shown that the observed increases in atmospheric green-
house gases may lead to global warming, sea-level rise, and space-time
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