4 ms·

Here's an analogy that may be worthwhile. We do not understand the physics of fluids very well. We are not even sure if their standard mathematical representati

Here's an analogy that may be worthwhile. We do not understand the physics of fluids very well. We are not even sure if their standard mathematical representation has general exact solutions. We don't understand the microscopic interactions of turbulence, and in many cases the system has a chaotic dependence on tiny fluctuations in the initial conditions. However, we do know that in the case of most fluids, with flows of a low Mach number, gases are largely incompressible. There, Bernoulli's equation holds, 1/2 density v^2 + density * g * height + pressure = constant. It might not be perfectly accurate, but it will lift airplanes into the sky! Bernoulli's equation doesn't work so well at boundary layers, such as those that form on the edges of wings. It doesn't work so well in regimes with a high Mach number, and therefore the air is compressed, such as on the edge of a propeller, or during supersonic flight. It doesn't operate so well under viscous flow. And it can't predict the turbulence which will alter the pressure and density, jostling passengers up and down in the air under rough winds. Yet none of those things have affected the overall direction of the results. Planes have lift. We do not claim that airplane designers do not understand this. We just say that there are gaps in the understanding. It is not known in detail. Similarly, greenhouse gas theory was only approximate. Throughout the study of climate science, people continue to add more and more to the simple physical theory, modifying the predictions in small ways. But throughout, some things have been constant. Climate change is driven by energy transfer. Energy comes from the sun, and is radiated back out by the earth. Greenhouse gases make that radiation by the earth less effective. This much isn't contested: the only question the magnitudes. And yet, people say that 'I don't believe in the CO2 theory' or that 'humans are not contributing significantly to global warming.' This is like people saying that kinetic energy isn't proportional to the square of the velocity, and therefore ignore those insolent 'physicists'. Of course, it isn't proportional to the square of the velocity, exactly. But it isn't far off, and it's a good enough approximation unless we have reason to believe otherwise. How much reason do we have to say that the standard climate models are erroneously showing a significant temperature delta due to CO2? Does anyone anywhere have a reasonable physical or ecological model that could saturate its effect? That could reverse its direction? The most intriguing was variations in the sun's luminosity, but that doesn't account for nearly enough.

npk 18y ago
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 18y ago
  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 18y ago
    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]

npk 18y ago

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 18y ago
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 18y ago
  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]