Climate Change 2001:
Working Group II: Impacts, Adaptation and Vulnerability
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Ecosystems are subject to many pressures (e.g., land-use change, resource demands, population changes); their extent and pattern of distribution is changing, and landscapes are becoming more fragmented. Climate change constitutes an additional pressure that could change or endanger ecosystems and the many goods and services they provide.

There now is a substantial core of observational and experimental studies demonstrating the link between climate and biological or physical processes in ecosystems (e.g., shifting range boundaries, flowering time or migration times, ice break-up on streams and rivers), most evident in high latitudes. Recent modeling studies continue to show the potential for significant disruption of ecosystems under climate change. Further development of simple correlative models that were available at the time of the Second Assessment Report (SAR) point to areas where ecosystem disruption and the potential for ecosystem migration are high. Observational data and newer dynamic vegetation models linked to transient climate models are refining the projections. However, the precise outcomes depend on processes that are too subtle to be fully captured by current models.

At the time of the SAR, the interaction between elevated carbon dioxide (CO2), increasing temperatures, and soil moisture changes suggested a possible increase in plant productivity through increased water-use efficiency (WUE). Recent results suggest that the gains might be small under field conditions and could be further reduced by human management activities. Many ecosystems are sensitive to the frequency of El Niño-Southern Oscillation (ENSO) and other extreme events that result in changes in productivity and disturbance regimes (e.g., fires, pest and disease outbreak).


Most global and regional economic studies—with and without climate change—indicate that the downward trend in real commodity prices in the 20th century is likely to continue into the 21st century, although confidence in these predictions decreases farther into the future (see Section 5.3.1).

Impacts Adaptation and Vulnerability

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