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2.2.4. Advances since the SAR and Future Needs
Since the SAR, methods have been developed and applied to the detection of
present impacts of 20th-century climate change on abiotic and biotic systems.
Assessment of impacts on human and natural systems that already have occurred
as a result of recent climate change is an important complement to model projections
of future impacts. How can such effects be detected? Such detection is impeded
by multiple, often intercorrelated, nonclimatic forces that concurrently affect
those systems. Attempts to overcome this problem have involved the use of indicator
species to detect responses to climate change and infer more general impacts
of climate change on natural systems. An important component of this detection
process is the search for systematic patterns of change across many studies
that are consistent with expectations on the basis of observed or predicted
changes in climate. Confidence in attribution of these observed changes to climate
change increases as studies are replicated across diverse systems and geographic
regions. Even though studies now number in the hundreds, some regions and systems
are underrepresented. However, there is a substantial amount of existing data
that could fill these gaps. Organized efforts are needed to identify, analyze,
and synthesize those data sets.
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