Climate Change 2001:
Working Group II: Impacts, Adaptation and Vulnerability
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19.8. Conclusions

This chapter focuses on certain reasons for concern with regard to what might be considered a "dangerous" climate change (reported as increases in global mean temperature; see Section 19.1.2). Each reason for concern can be used by itself or in combination with other reasons for concern to examine different aspects of vulnerability to climate change. We offer no judgment about how to use some or all of these reasons for concern to determine what is a dangerous level of climate change. The reasons for concern are as follows:

  1. The relationship between global mean temperature increase and damage to or irreparable loss of unique and threatened systems
  2. The relationship between global mean temperature increase and the distribution of impacts
  3. The relationship between global mean temperature increase and globally aggregated impacts
  4. The relationship between global mean temperature increase and the probability of extreme weather events
  5. The relationship between greenhouse concentrations and the probability of large-scale singular events.

In addition, we address what observed effects of climate change tell us with regard to Article 2 of the UNFCCC. We review the state of knowledge with regard to what observations and each reason for concern tell us about climate change impacts.

19.8.1. Observations

Based on a review of the literature of observations of climate change impacts, as reflected in other TAR chapters, we conclude:

There is preliminary evidence that unique and threatened systems are beginning to be affected by regional climate change and that some systems have been affected by recent increases in extreme climate events in some areas. Many high-latitude and high-altitude systems are displaying the effects of regional climate change. It is difficult to define observed impacts at aggregate levels, and evidence of large-scale singular events occurring as a result of recent climate change is lacking.



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