The Greenhouse Effect is the resistance the atmosphere imposes on the cooling of the earth’s surface. Increasing the Greenhouse Effect results in increased earth surface temperature.
The Greenhouse Effect can be expressed in any of the three terms, relative to what the Earth’s heat loss rate to space would be if there were no Greenhouse elements:
- Upward Heat Flux, presently 139 watts/m^2
- Tempeerature Increase, presently 31C
- A coefficient, between 0 (no Greenhouse effect) and 1 (total insulation of earth’s surface), or fraction of earth’s upward infrared radiation impeded by the effect, presently = 0.365
Earth’s surface heat must find its way to outer space in order to reject the solar heat it absorbs. The earth, at its surface, is cooled by radiation (infrared), convection (primarily winds), conduction, and evaporation of surface water. But all the absorbed solar heat is eventually ejected to space by infrared radiation.
Some of the earth’s surface is warmed by the downward re-irradiation of heat absorbed by the water in clouds, which intercept surface cooling radiation. Condensation of evaporated (mainly sea-) water also adds heat to the atmosphere. Radiative heat loss is also impeded by the absorption of outgoing infrared radiation by greenhouse gases.
The atmosphere is often divided into four layers:
- The troposphere is that lower part of the atmosphere where water can exist in the liquid phase, as clouds or rain
- is bounded by the earth’s surface and the tropopause.
- contains 80% of atmosphere’s mass and 99% of its water.
- The stratosphere, mesosphere and thermosphere which are the remaindner of the atmosphere lying between the tropopause and outer space.
In order to maintain its surface temperature, the earth must reject as much heat (as infrared radiation) as it absorbs as light from the sun. That heat balance is depicted below. See that as the greenhouse resistance increases, the earth’s surface temperature must increase to maintain the balance.
The chart above is dimensionally misleading. The earth’s atmosphere is only 50 miles high, most of its air residing within 5 miles. Whereas the radius of the earth is about 4,000 miles. See figure below. The yellow spot is the sun, 93 million miles away!