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Re: [Phys-L] just for fun?



Looking at historical data going back hundreds of thousands of years seems to imply a different feedback than many have stated. The more obvious cycles start with a rise in temperature followed a few hundreds or possibly a thousand years later by a sharp rise in CO2. But when the CO2 rises, the temperature plummets. That implies a negative feedback - not a positive loop of temperature --> CO2 --> temperature, etc. On the other hand, I doubt if this has any meaning when discussing AGW. Natural temperature<--> CO2 forcing probably has little to do with the results human production of CO2.

Bob at PC

-----Original Message-----
From: Phys-l [mailto:phys-l-bounces@phys-l.org] On Behalf Of Folkerts,
Timothy J
Sent: Monday, January 06, 2014 12:59 PM
To: Phys-L@Phys-L.org
Subject: Re: [Phys-L] just for fun?

John M says
I've never understood this talking point. To first order rising
temperatures lead to rising levels of CO2 and rising levels of CO2 lead
to rising temperatures. As John Denker has already pointed out, it's a
positive feedback loop.

There are a few negative feedbacks as well. A couple of the more obvious
ones to me are:

Rising temperatures --> more evaporation --> higher albedo --> cooling More
CO2 --> plants grow better --> CO2 pulled from atmosphere --> cooling

The warming from CO2 itself is not strongly contested (except by some on
the fringe of climate denialism). Generally people calculate that doubling
CO2 will lead to ~ 1 C warming by itself, due directly to the radiative effects of
the CO2. That is the 'simple' physics of "radiative forcing".

The more complicated climate science tries to estimate the impact of
feedbacks. Those estimates typically vary from ~ 0.5 C to ~ 5 C for the overall
impact with feedback -- ie the "climate sensitivity" is between 0.5 and 5,
which is a huge range. The IPCC puts the estimates in the range 2-4.5, which
is still a pretty big range. Even relatively uncertain things in physics like the
mass of the top quark or Higgs boson are given to within ~ 1%, not ~ 100%, so
I tend to remain open-minded about the actual sensitivity.
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