> Over the globe there is a range of ~100C in the instantaneous (even
> seasonal average) temperature and ~500W/m^2 in the incident radiation,
> so the odd watt or 3 isn't really that big a deal. Even if sensitivity
> was strongly nonlinear such that hot areas warmed up 10x as much as
> cold ones, shifting the whole global surface by 3W or 6W would be much
> closer to a linear response.
I see this for a simple continuous function, but why is the response
curve simple and continuous?
Say, mightn't forcing that's concentrated over land areas (from local
aerosol pollution or land use change) induce somewhat different
feedbacks (less water vapour feedback comes to mind)?
Or if a wind regime (say the jet stream) is affected, mighn't that
lead to a particular feedback (say more Saharan dust, or local drought
killing of low albedo forest and replacing it with high albedo salt
desert) that only occurs at a threshold value, or in any case makes
the response curve strongly non linear (say the Saharan dust would
mitigate temperature increase strongly between 1 and 1.5 C temperature
rise, and be negligible above and below)?
I see how the carbon cycle and icesheet feedbacks are dealt with. They
are simply turned into forcings, which are fixed, and thereby these
elements of non-linearity are removed. And maybe we can just do the
same for Saharan dust or drought induced albedo changes (or maybe
these are inconsequential?), but for clouds and wind?
It isn't obvious to me why a world that is say 3C warmer couldn't have
a dramatically different cloud distribution/appearance, sufficiently
so that this feedback might add/subtract 5 W/m2 in addition to the
water vapour feedback.
Is this feedback somehow excluded as well (by holding cloud albedo
constant???), or is there a good reason to presume that cloud response
and water vapour response to increased temperature will be smooth? (I
know water vapour will be perfectly smooth at 100% saturation in a
small vessel that contains both water and air and the temperature of
which is varied, but the atmosphere isn't like that? "Smooth" in this
context means simple continous function, in the case of vapour
pressure it'll approximate some sort of exponential function over a
100C span and will be reasonably linear over a 5C span)
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