Global Warming 101


Global Warming Theory in a Nutshell

Every scientific theory involves assumptions. Global warming theory starts with the assumption that the Earth naturally maintains a constant average temperature, which is the result of a balance between (1) the amount of sunlight the Earth absorbs, and (2) the amount of emitted infrared (”IR”) radiation that the Earth continuously emits to outer space. In other words, energy in equals energy out. Averaged over the whole planet for 1 year, those energy flows in and out of the climate system are estimated to be around 235 or 240 watts per square meter.

Greenhouse components in the atmosphere (mostly water vapor, clouds, carbon dioxide, and methane) exert strong controls over how fast the Earth loses IR energy to outer space. Mankind’s burning of fossil fuels creates more atmospheric carbon dioxide. As we add more CO2, more infrared energy is trapped, strengthing the Earth’s greenhouse effect. This causes a warming tendency in the lower atmosphere and at the surface. As of 2008, it is believed that we have enhanced the Earth’s natural greenhouse effect by about 1%.

Global warming theory says that the lower atmosphere must then respond to this energy imbalance (less IR radiation being lost than solar energy being absorbed) by causing an increase in temperature (which causes an increase in the IR escaping to space) until the emitted IR radiation once again equals the amount of absorbed sunlight. That is, the Earth must increase its temperature until global energy balance is once again restored. This is the basic explanation of global warming theory. (The same energy balance concept applies to a pot of water on a stove set on “low”. The water warms until the rate of energy loss through evaporation, convective air currents, and infrared radiation equals the rate of energy gain from the stove, at which point the water remains at a constant temperature. If you turn the heat up a tiny bit more, the temperature of the water will rise again until the extra amount of energy lost by the pot once again equals the energy gained from the stove, at which point a new, warmer equilibrium temperature is reached.)

Now, you might be surprised to learn that the amount of warming directly caused by the extra CO2 is, by itself, relatively weak. It has been calculated theoretically that, if there are no other changes in the climate system, a doubling of the atmospheric CO2 concentration would cause less than 1 deg C of surface warming (about 1 deg. F). This is NOT a controversial statement…it is well understood by climate scientists. (As of 2008, we were about 40% to 45% of the way toward a doubling of atmospheric CO2.)

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