Sunday, June 17, 2012

A more reasonable statement of climate change uncertainty

From the same magazine that drew my contempt:

The main uncertainties involve what might happen as carbon-dioxide levels reach 450 ppm and above. In particular, the question is how and when “positive feedback” loops would kick in, so that the hotter things get, the faster they will get even hotter. …
“The reality of it is that in many cases, there may not be any fixed threshold for ‘irreversible’ change,” Michael Mann told me. “What we have with rising CO2 levels in general is a dramatically increasing probability of serious and deleterious change in our climate.” He went down the list: more frequent, severe, and sustained heat waves, like those that affected Russia and the United States this summer; more frequent and destructive hurricanes and floods; more frequent droughts, like the “thousand-year drought” that has devastated Australian agriculture; and altered patterns of the El NiƱo phenomenon, which will change rainfall patterns in the Americas. In other cases, he said, there could be important thresholds. For example, the possibility of dramatic rises in ocean levels, which could affect the habitability of New York, London, Shanghai, Miami, the entire Netherlands, and many other modern conurbations, along with coastal areas in India, Bangladesh, and elsewhere. “It would be nice to know where such thresholds are so we can avoid crossing them,” Mann said. “We can’t know that. What we do know for certain is that with each fraction of a degree of warming, the probability of such potentially catastrophic outcomes goes up.”

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