This link is to an interesting comment at Watts Up With That analyzing the difficulty of deciding whether the interaction of CO2 (a weak greenhouse gas) with water vapor (a much stronger greenhouse gas) produces a negative feedback loop, which would tend toward equilibrium, or a positive feedback loop, which would spiral into permanent warming. The question is fraught, because water vapor can serve either to warm the atmosphere, via the greenhouse effect, or to cool it, via other well-observed mechanisms. When all the dust settles, how do these effects net out?
All alarmist climastrology in recent decades has depended on climate models that assume a net positive sign on the "feedback" or "sensitivity" factor; most of the quarreling has been over the size of the factor, especially since the past 17 years of little or no warning have demonstrated that the factor has been grossly overestimated. In fact, however, there's scant evidence one way or the other on the more fundamental question of whether the feedback is negative or positive. No amount of tinkering with the exact size of the positive feedback factor will help the models' ability to predict real experience if the problem really is that the feedback is negative.
2 comments:
On that atmospheric CO2/water vapor feedback loop: it's true enough that atmospheric CO2 has risen (slightly) over the last several decades. But the atmospheric water vapor actually has fallen since the late '40s.
Frankly, I think the long-term sign on the feedback loop flips based on a number of other, external signals, including, but not limited to the sun's spot cycle (both its short-term subcycle and its long-term cycle); where we are in the cosmic ray incidence cycle; short term shocks like aerosol dust from drought, volcanism, and how much these coincide or contradict each other as they overlap; etc.
Eric Hines
Good points, both.
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