Top and Bottom of the Atmosphere

By Willis Eschenbach – R$e-Blogged From WUWT

Some days I learn a lot. Today was one of them. Let me start at the start. Back in 1987 in a paper entitled ‘The Role of Earth Radiation Budget Studies in Climate and General Circulation Research“, a prescient climate scientist yclept Veerabhadran Ramanathan pointed out that the poorly-named “greenhouse effect” can be measured as the amount of longwave energy radiated upwards at the surface minus the upwelling longwave radiation at the top of the atmosphere, viz:

The greenhouse effect. The estimates of the outgoing longwave radiation also lead to quantitative inferences about the atmospheric greenhouse effect. At a globally averaged temperature of 15°C the surface emits about 390 W m -2, while according to satellites, the long-wave radiation escaping to space is only 237 W m -2. Thus the absorption and emission of long-wave radiation by the intervening atmospheric gases and clouds cause a net reduction of about 150 W m -2 in the radiation emitted to space. This trapping effect of radiation, referred to as the greenhouse effect, plays a dominant role in governing the temperature of the planet. 

And here is what Ramanathan was talking about:

Figure 1. All-sky (both cloudy and clear) greenhouse effect. In climate science, “upwelling” means headed for space, “downwelling” means headed for the surface, “forcing” means a change in downwelling radiation, “LW” is thermal longwave radiation, and “SW” is solar shortwave radiation. 

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