Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

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.