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Physics
Conservation of Energy
- Precludes runaway greenhouse effects
- Atmospheric absorption has no effect on the energy budget, i.e. Energy in == Energy out
Clouds and greenhouse gases, warm surface
- Clouds trap far more energy than greenhouse gases
- Greenhouse gases redistribute atmospheric energy
- Greenhouse gas effects are primarily diurnal
Notes:
Greenhouse gases act primarily to retain heat from day to night. Hot muggy nights and radiational cooling on clear winter nights illustrate the limits of the greenhouse effect.
A secondary effect of greenhouse gases is to redistribute energy within the atmosphere.
Water vapor absorption is strong enough that it's retained heat can last throughout the night, while heat captured by CO2 doesn't persist very long. Radiational cooling, which illustrates the decay rate of the CO2 related greenhouse effect, generally only occurs when the greenhouse contribution of water vapor is minimized and there's no cloud cover.
Clouds keep the surface warm by absorbing surface heat and reradiating some of it back. The warming influence at night is larger than the daytime cooling influence resulting from blocked sunlight. This is because clouds absorb a significant amount of solar energy, much of which is eventually reradiated back to the surface.