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Let me push back on the notion that there are alternative explanations besides increased concentration of atmospheric CO2 and other greenhouse gases for the cur

Let me push back on the notion that there are alternative explanations besides increased concentration of atmospheric CO2 and other greenhouse gases for the current rapid changes in climate. It's one thing to say that we should distrust the complicated models that try to simulate the entire Earth in sufficient detail to predict exactly what the temperature change will be and what the impacts will be in each region. That stuff is genuinely hard to predict and I won't be surprised if the models get lots of things wrong. But the basic mechanism by which higher CO2 concentrations enable to atmosphere to retain heat better is dead simple. Heat is lost from the ground and atmosphere by low frequency photons that radiate away into space. Many of the photons, especially those emitted from the ground and lower parts of the atmosphere will be scattered by gas molecules in the atmosphere, and CO2 is one of the gases that is particularly good at this. Scattering means that the photon's direction changes randomly, which means that there's a good chance that it will be redirected to be heading back down towards the ground, rather than out into space. So an increased number of scattering events improve heat retention. Adding more CO2 to the atmosphere increases the number of of scattering events and thus results in less heat being lost to space, which results in a higher average* temperature for the Earth. We can debate what the exact consequences of all this will be, but saying it isn't a result of humanity burning large quantities of fossil fuels is to me tantamount to an admission that you don't understand physics. *(Technically, since thermal radiation goes as T^4 times emissivity and some other stuff, what I really mean is a higher value of T^4 averaged across the surface area of the Earth and weighted by emissivity. And even this is an oversimplification, since not only can heat be lost from the ground, but also the atmosphere iteself. But the basic picture of "planet gets warmer" is still correct.)

machina_ex_deus 4y ago
I really don't like the way the narrative is presented. First of all, the radiation is thermal radiation. Air with CO2 at close temperature to the surface emitting thermal radiation has no bad effect whatsoever on how fast the energy radiates out. Two things at the same temperature will always be at equilibrium, and the least thermal radiation you can emit is black body radiation like the surface. So the narrative of looking at it like it's radiation scattering might be true for high up in the atmosphere where the temperature difference from the surface is high - but very misleading and leads to bad intuition in low attitudes. CO2 also tends to stay in lower attitudes. There are other effects from CO2 that also go the other way. CO2 has increased heat capacity, it's heavier than air, and it might have a cooling effect because it increases the effectiveness of convection. What's the leading cause? By how much? I don't know. You need to do the calculation properly and find out. This is physics not humanistic subject. You don't judge with narratives. Narratives are misleading, calculations are what matters. If you bring your narrative to the calculation and the only effect of CO2 in your calculation is the radiation, that's even worse. Thermodynamic systems also tend to reach equilibrium, so if you have errors in any parameters in the description of the system, your errornous system with the current state of the real system will be out of equilibrium in the errornous simulation. You should always expect simulations with imprecise data to be less stable than the real system itself.
- mempko 4y ago
  It's settled, greenhouse gases, primarily CO2 but also water vapor, methane, and others, is causing warming. There isn't any uncertainty about this. Also, no, simulations are not always less stable than the real system.

machina_ex_deus 4y ago

I really don't like the way the narrative is presented. First of all, the radiation is thermal radiation. Air with CO2 at close temperature to the surface emitting thermal radiation has no bad effect whatsoever on how fast the energy radiates out. Two things at the same temperature will always be at equilibrium, and the least thermal radiation you can emit is black body radiation like the surface. So the narrative of looking at it like it's radiation scattering might be true for high up in the atmosphere where the temperature difference from the surface is high - but very misleading and leads to bad intuition in low attitudes. CO2 also tends to stay in lower attitudes. There are other effects from CO2 that also go the other way. CO2 has increased heat capacity, it's heavier than air, and it might have a cooling effect because it increases the effectiveness of convection. What's the leading cause? By how much? I don't know. You need to do the calculation properly and find out. This is physics not humanistic subject. You don't judge with narratives. Narratives are misleading, calculations are what matters. If you bring your narrative to the calculation and the only effect of CO2 in your calculation is the radiation, that's even worse. Thermodynamic systems also tend to reach equilibrium, so if you have errors in any parameters in the description of the system, your errornous system with the current state of the real system will be out of equilibrium in the errornous simulation. You should always expect simulations with imprecise data to be less stable than the real system itself.

mempko 4y ago
It's settled, greenhouse gases, primarily CO2 but also water vapor, methane, and others, is causing warming. There isn't any uncertainty about this. Also, no, simulations are not always less stable than the real system.