6. Carbon dioxide has little influence on Earth’s surface temperature. Earth’s surface temperature is elevated because the radiation emissions from the greenhouse gases, clouds, and aerosols reaching the surface reduce the net longwave radiation loss from the surface. Additional carbon dioxide concentration in the atmosphere has little impact on surface temperature because there is little change in longwave radiation reaching the tropical surface as carbon dioxide concentration increases. The calculations below are made using the MODTRAN radiation transfer model and are for the tropical atmosphere with no clouds and constant temperature. Since industrialisation, for each 100ppm increase in carbon dioxide concentration the increase in radiation emitted by the greenhouse gases and reaching the surface was about 0.6W/m2. That is an increase of 0.3 percent of the radiation emitted by water vapour. Note that from the last glacial maximum 20,000 years ago to preindustrial times the carbon dioxide concentration increased from near 200ppm to near 300ppm (an increase of only 100ppm). During this period the polar ice sheets covering much of North America and northern Europe melted and sea level rose about 130 metres. Since industrialisation the carbon dioxide has increased by more than 100ppm, but sea level rise has been insignificant. The evidence does not suggest carbon dioxide concentration is influential in changing Earth’s climate.

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