Richard wrote:
Even the very "simple" argument that carbon dioxide levels in the atmosphere (and there is no doubt that CO2 levels have been rising because of humans but as to whether this is greater than even a single major volcanic event is questionable) cause warming relies on assumptions that may be quite false. More CO2 and it is possible you get more refraction at the equator (warming), but also more cloud (warming in the short term - seriously cooling in the longer term), a change in the albedo readings at all latitudes (warming or cooling depending on your theory). An this does not even take into account changes in so many other factors. The trouble is the study of climate with respect to these factors is all very new.
I think that this is the most important point where I would disagree with you. The effects of increasing CO_2 levels is huge and that makes global warming a predictable effect. Without any greenhouse gasses in the atmosphere, temperatures would be 33 ?C lower than they are today. It is likely that we are going to double the CO_2 concentration in the atmosphere, from 0.027% to more than 0.05% or more.
Strong feedback effects limit the temperature increase to just a few degrees ?C. But it is just not possible to have zero or negative temperature increase, because those feedback mechanisms only work because the average temperature has increased in the first place. You get more clouds because at higher temperatures you get more evaporation.
Global warming is ultimately just a consequence of conservation of energy. The exact temperature increase is model dependent, but the fact that it exists is not. By increasing Co_2 levels you effectively pump more energy in the atmosphere per unit time. Different climate models will make different predictions; the fact that these models can be criticised for not being 100% realistic does not invalidate the predicted global warming.
Similarly, if I turn on the heating now, then the temperature in my room will increase. I could write down a model for the thermal convection in my room, the thermal conduction through the walls and the convective heat transfer from the walls to the outside air, but the result of all those calculations will be that the temperature in my room will increase. Criticism about the simplified way of modeling the heat transfer would not invalidate the prediction of a temperature increase.
