6 suggests that t < 100 years is incompatible with = 4°C.5 Indeed, reference to Figure 3 suggests that t < 16 years corresponds roughly to g 0.5 and < 0.6°C.

Certainly, these matters require more careful analysis. However, the present remarks suggest that consideration of a variety of known climate-forcing perturbations as probes of the climate system may allow the use of a simple methodology for constraining our expectations for greenhouse warming. For example, if responses to volcanos imply short characteristic ocean delays, then we would also expect small climate responses to increasing CO2. One will of course want to understand in detail the physics determining climate sensitivity. However, this hardly justifies ignoring the possibility that it may be possible to bypass these details in approaching the issue of sensitivity directly.


I should like to acknowledge the support of the National Science Foundation under Grant 8520354-ATM and of the National Aeronautics and Space Administration under Grant NAGW-525.


Conceivably, support for this conclusion might also emerge if the climate response to volcanos tends to peak at one year rather than two years after eruption (viz., Figure 7).

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