Lindzen continues :
"Thus, the claim that models cannot account for recent warming without external forcing is held to imply the role of human forcing. To be sure, current models can simulate the recent trend in surface temperature, but only by invoking largely unknown properties of aerosols and ocean delay in order to cancel most of the greenhouse warming (Schwartz et al., 2007). Finally, we note substantial corroborating work showing low climate sensitivity.
Ultimately, however, one must recognize how small the difference is between the estimation that the anthropogenic contribution to recent surface warming is on the order of 1/3, and the iconic claim that it is likely that the human contribution is more that 1/2. Alarm, we see, actually demands much more that the iconic statement itself. It requires that greenhouse warming actually be larger than what has been observed, that about half of it be cancelled by essentially unknown aerosols, and that the aerosols soon disappear. Alarm does not stem directly from the iconic claim, but rather from the uncertainty in the claim, which lumps together greenhouse gas additions and the cancelling aerosol contributions (assuming that they indeed cancel warming), and suggests that the sum is responsible for more than half of the observed surface warming. What this paper attempts to do is point the way to a simple, physically sound approach to reducing uncertainty and establishing estimates of climate sensitivity that are focused and testable. Such an approach would seem to be more comfortable for science than the current emphasis on models testing models, large ranges of persistent uncertainty, and reliance on alleged consensus. Hopefully, this paper has also clarified why significant doubt persists concerning the remarkably politicized issue of global warming alarm."
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