[npk]

The point is that climate models are not testable. Bernoulli's equation is a "good" approximation because we know when it fails.

If we're going to rely on climate models to define policy, we should understand what they're good for. You say that 0.5 m v^2 is a good enough approximation until we say otherwise, but the same statement doesn't apply to climate models. The models are complicated, nonlinear, and the scientists running them have pressure to produce certain results.

[DaniFong]

Climate models are testable. It just takes a long time to test them, since they describe long term behavior. Fluid dynamics is nonlinear, and complicated, but certain effects, such as lift, or drag, are both simple and broadly applicable. So it is with radiative models of global heat balance. Heat powers the climate! Altering CO2 will alter the flux of infrared radiation which will alter the flux of heat. This basic mechanism is uncontested. I could be that the total heat flux doesn't change much because it's balanced by other effects. But we know of no other effects sufficiently strong to render the temperature change small. If we have a physically plausible model that fits measured datapoints, and we keep check its predictions against measurements, and we keep asking 'in which ways might this be different?' and looking for possible problems, or effects that we've missed, then this is science at work. If instead we say "it's complicated, and there are some areas in which there are gaps in understanding, therefore we should draw no conclusions and make no decisions," we achieve little.

[yters]

This is tangential, but you seem like you are informed on the climate debate, unlike myself. Feel free to ignore this if you consider it a troll, or that I'm bringing up tired and often refuted points.

Anyways, I've been reading a climate change skeptic, James Hogan, and he makes a pretty interesting claim. James says that 90% of the earth's warming is caused by water vapor. Of the carbon dioxide that does contribute to warming, only about 2% (as I recall) of it is human contributed. I haven't checked his sources, but these numbers seem pretty hard to fudge. That means we contribute at most 0.2% to the earth's warming with our carbon dioxide.

James also made a number of other points, like the measurements used to prove global warming are taken around developing areas, and more objectively obtained warming and carbon cycles show very strong correlations with solar activity. But, the water vapor point stood out the most in my mind and seems to clearly demonstrate we're overreacting.

Is there some kind of fallacy that I'm missing? Am I significantly underestimating the potential for that 0.2% to push us over some kind of tipping point? Thanks for any input you can give.

[edited a couple times b/c I'm too tired to do basic math]

[DaniFong]

The IPCC models do account for both water vapor and solar irradiation. Water vapor is the dominant greenhouse gas. It is roughly correct to say that it accounts for 90% of the greenhouse effect (the lowering of infrared flux from the earth to space). However, it's not correct to say that 90% of the earth's warming is due to water vapor, if what one means by warming is change in average temperature over time. The amount of water vapor has apparently not changed very much.

Here's some figures tabulated from the standard models, from the fourth IPCC working group is found here:

http://ipcc-wg1.ucar.edu/wg1/docs/WG1AR4_SPM_PlenaryApproved...

And a nice graph can be found here:

http://en.wikipedia.org/wiki/Image:Radiative-forcings.svg

These figures are estimates of anthropogenic forcing, in other words, how the components of the heat flux of the world changed due to the ecological changes. There are quite a few things here which can be measured quite accurately: cloud albedo being one, stratospheric water vapor content being another.

These were estimates made in 2005. According to them, additional stratospheric water vapor accounts for less than a twentieth of a watt per square meter, and variation in solar activity less than a tenth. Anthroprogenic carbon dioxide accounts for around 1.7 watts per square meter, averaged over the year, over the earth.

Solar activity is a large component, but recent estimates point at it accounting for only '18 and 36% of warming from 1950 to 1999' http://climate.envsci.rutgers.edu/pdf/StottEtAl.pdf

As for the claims that measurements of global warming are taken around developing areas, I think that claim is most fraudulent. First of all, one can measure the surface heat quite accurately by satellite by looking at the ratio of radiation in different 'infrared windows'. This allows you to calculate, via the Stefan-Boltzmann radiation law, the temperature at a surface.

Second of all, and perhaps more obviously, nearly all glaciers and icecaps are melting or receding, and these are not exactly developing areas! Melting ice-caps are measurements too!

[yters]

Much appreciated.