That this specific question warrants attention is illustrated by the recent prominent claims of one former U.S. vice president, claims that melting of 20% of the Earth's ice caps pose an imminent threat (e.g. that the Beijing area may have to be "evacuated"). Such claims are repudiated by the scientific literature, including such reviews as the IPCC TAR.
The issue is not whether humans contribute to global change, but what is the magnitude and nature of this contribution and how does it compare to other contributions. The observed correlation between greenhouse gases and temperature over the last four glacial cycles, for example, is not informative unless we understand the casual relationship, the nature of both positive and negative feedbacks over shorter timescales than the resolution of the Vostok ice core, etc. In the particular context of global climate change, substantial issues remain with regard to conclusions of the IPCC. While I cannot make specific comments regarding the cited IPCC 4th Assessment Report until it is made available, I do not predict that these issues will be adequately addressed.
Regarding sea-level change, there is need to distinguish between observed changes and predicted future changes which are based indirectly on global circulation models. For instance, hypothesized changes based on IPCC TAR estimates of future sea level rise are necessarily dependent on the accuracy of the models used to produce those sea level rise estimates.
(posted at Climate Change Blog, September 2006)
© 2006 by Wm. Robert Johnston.
Last modified 24 October 2006.
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