The Earth's average surface temperature is about 33°C warmer than it would be without the greenhouse effect. The Earth reflects about 30% of the incoming solar radiation. The remaining 70% is absorbed, warming the land, atmosphere and oceans.
For the Earth's temperature to be in steady state so that the Earth does not rapidly heat or cool, this absorbed solar radiation must be very nearly balanced by energy radiated back to space in the infrared wavelengths.
The infrared photons emitted by the surface are mostly absorbed in the atmosphere by greenhouse gases and clouds and do not escape directly to space so the surface temperature will rise until it generates thermal radiation equivalent to the sum of the incoming solar and infrared radiation.
Anthropogenic Global Warming, a recent warming of the Earth's lower atmosphere, is believed to be the result of an 'enhanced greenhouse effect' mainly due to human-produced increased concentrations of greenhouse gases in the atmosphere and changes in the use of land.
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