2. Heat Energy and Temperature

Our relatively high global atmospheric temperature near the surface of the Earth, with an average of 14 to 15 degrees C, is caused by heat-absorbing gases in the atmosphere, mainly H2O vapor. Without the Earth's atmosphere the surface temperature would be approximately -18 degrees C.

The Earth receives about 1368 W/m2 of radiative heat from the Sun. The total amount of this heat withheld, approximately 11%, in the Earth's lower atmosphere, has traditionally been named the Earth's "Greenhouse Effect". For a cloudless atmosphere this effect is on the average about 146 W/m2 for the Earth, with an uncertainty of ± 5 to 10 W/m2 due to analytic uncertainties and natural climatic variations. All human activities have been claimed to contribute about 1.3% of this (approx. 2 W/m2), while a hypothetic doubling of the atmospheric CO2 concentration would contribute about 2.6% (approx. 4 W/m2) to the present "Greenhouse Effect" (Raval & Ramanathan, 1989; Ramanathan et al., 1989).

150 year long time series of temperature measurements are covering too short time spans to be useful for climate prediction, in order to be used as "evidence" for anthropogenic heating (or cooling). The global mean temperature has risen and fallen several times over the last 400 years, with no evidence of anthropogenic causes, although strong explosive volcanic eruptions have caused periodically colder climates (Jaworowski et al., 1992 a).

It should also be noted that clouds can reflect up to approx. 50 W/m2 and can absorb up to approx. 30 W/m2 of the solar radiation (Ramanathan et al., 1989), making the Earth's average "Greenhouse Effect" vary naturally within approx. 96 and 176 W/m2. Hence the anticipated anthropogenic atmospheric CO2 heat absorption is much smaller than the natural variation of the Earth's "Greenhouse Effect" (Segalstad & Jaworowski, 1991).

The oceans act as a huge heat energy buffer; the global climate is primarily governed by the enormous amount of heat stored in the oceans (total mass approx. 1.4 x 1024 g), rather than the minute amount of heat withheld in the heat-absorbing part of the atmosphere (total mass approx. 1.4 x 1018 g), a mass difference of one million times (Peixoto & Oort, 1992). Most of the atmospheric heat absorption occurs in water vapor (total mass approx. 1.3 x 1019 g), which is equivalent to a uniform layer of only 2.5 cm of liquid water covering the globe, with a residence time of about 9 days (Peixoto & Oort, 1992).

The total internal energy of the whole ocean is more than 1.6 x 1027 Joule, about 2000 times larger than the total internal energy 9.4 x 1023 Joule of the whole atmosphere. Note that this energy is defined with respect to 0 degrees Kelvin (Peixoto & Oort, 1992).

Furthermore the cryosphere (ice sheets, sea ice, permafrost, and glaciers; total mass of the continental ice is approx. 3.3 x 1022 g) plays a central role in the Earth's climate as an effective heat sink for the atmosphere and oceans, with a large latent heat of melting on the order of 9.3 x 1024 Joule, a hypothetic energy equivalent to cooling the entire oceans by about 2 degrees C (5.8 x 1024Joule/degree C). For comparison, the energy needed to warm the entire atmosphere by 1 degree C is only 5.1 x 1021 Joule (Oerlemans & van der Veen, 1984).

Hence it will be impossible to melt the Earth's ice caps and thereby increase the sea level just by increasing the heat energy of the atmosphere through a few percent by added heat absorption of anthropogenic CO2 in the lower atmosphere.

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Last Updated June 20, 1997