How the World Really Works: The Science Behind How We Got Here and Where We're Going

by Vaclav Smil

The Earth’s atmosphere absorbs the incoming (short-wave) solar radiation and radiates (longer waves) to space. Without it, the temperature of the Earth would be -18°C, and hence our planet’s surface would be perpetually frozen. Trace gases change the planet’s radiation balance by absorbing some of the outgoing (infrared) radiation and raising the surface temperature. This allows for the existence of liquid water, whose evaporation puts water vapor (another gas that absorbs outgoing infrared, invisible waves) into the atmosphere. The overall result is that the Earth’s surface temperature is 33°C higher than it would be in the absence of trace gases and water vapor, and the global mean temperature of 15°C supports life in its many forms.