I am teaching a class at NYU this Spring that I am loving: It is called (with grandiosity) The Art and Science of Approximate Reasoning: Physics, Sustainable Energy, and the Future of Humanity. We are computing what we can about sustainability, from a physics perspective and with order-of-magnitude reasoning. The strangest thing about the class (for me) is that it is a writing class. So I am grading writing assignments, something I am certainly not qualified to do.
I have learned a huge amount in this class. Here's one tiny, tiny example:
How does a greenhouse work, and is it anything like how the greenhouse effect on Earth works? The answer is extremely cool. In both cases (greenhouse and greenhouse effect) the system permits visible radiation to enter, but deters infrared radiation from escaping. In this sense, the two effects are very similar.
However, there are critical differences: In the case of the greenhouse, much of the effect is that the glass walls cut off convective cooling to the upper atmosphere. That is, they trap the heat near the heated ground, not letting it mix with the rest of the atmosphere. This effect probably dominates over the infrared-reflectance effect of normal glasses and plastics. The fundamental point is that (to first order) the Sun heats the Earth, which then heats the atmosphere. If part of the Earth is put inside a glass box, that part gets to hold its heat without sharing it entirely with the surrounding atmosphere. And indeed, greenhouses control their temperatures through ventilation management (management of convection to the outside).
In the case of the greenhouse effect, increasing the CO2 (and water and methane and so on) in the atmosphere increases the opacity at infrared wavelengths, so the Earth can't cool radiatively as efficiently as when the atmosphere is more infrared-transparent. That certainly is an effect in greenhouses, but not the only effect, and probably not the dominant effect.
The Earth's atmosphere can only cool (to space) radiatively, so the greenhouse effect is purely an adjustment of that radiative cooling. The human-built greenhouse can cool radiatively or convectively, and it uses both of those mechanisms for heat management.
