Question No. 24

One can often hear that carbon dioxide is responsible for the greenhouse effect, so that the more CO2 we have, the greater the greenhouse effect becomes. Then I have the following question. On Mars the proportion of CO2 in the atmosphere is 95% but there is no greenhouse effect there. Why do then people panic about the greenhouse effect on Earth, where the atmospheric CO2 content is the tiny 0.036%?
Answered 28 July 2009.
Question author: Andrei N.
Asked 22 May 2009.

These figures should be complemented by the statement that the density of atmospheric column on Mars is more than a hundred times less than on Earth. Despite that, as follows from the above figures, the absolute concentration of carbon dioxide in the atmosphere of Mars is over twenty times greater than on Earth. The greenhouse effect, defined as the share of thermal radiation of the planet surface reflected by the atmosphere back to the surface, is six times less on Mars than on Earth. Already from this observation one can unambiguously conclude that the greenhouse effect on Earth is largely determined by substances other that carbon dioxide. And, indeed, as is well-known, the major greenhouse substance in the atmosphere of Earth is water present in the form of water vapor and clouds.

The absorption band of CO2 intercepts only 19% of the Earth’s thermal spectrum. If, at the same overall density, the terrestrial atmosphere mostly consisted of CO2 as on Mars, the greenhouse effect would not exceed 19%. Note that in this case (at an absolute CO2 concentration exceeding the modern one by three thousand times) all thermal radiation of the planetary surface corresponding to the absorption band of carbon dioxide would be re-directed by the atmosphere back to the surface. Martian temperature is lower than that of the Earth. The absorption band of CO2 appears to be closer to the left border of the thermal spectrum such as the share of the planetary thermal spectrum covered by this band is lower compared to Earth’s 19%. In the result, Martian greenhouse effect is only 7%. The greenhouse effect on Earth is equal to 40%. This magnitude is by more than 90% determined by water vapor and clouds. The increase of atmospheric CO2 concentration by 30% compared to the preindustrial value cannot cause Earth's temperature to rise due to an increase in the greenhouse effect.

Modern panic around the growing CO2 is in reality caused by the fact that the developed countries have ultimately recognized their catastrophic economic dependence on the countries oil importers. On the wave of peoples’ sincere concern about the planetary futures the ruling circles of the developed countries are hoping to somehow reduce that dependence by exploring, at the expense of the tax payers, the economically uncompetitive domestic alternative energy sources, see here for more details.