The "greenhouse gases" intercept a fraction of outgoing terrestrial infrared radiation, creating the natural greenhouse effect which warmed the atmosphere by approximately 32ƒ Celsius at the beginning of the 20th Century. The activities of mankind have caused several of these gases to increase in atmospheric concentration during the past century, raising the atmospheric temperature by another 0.7 ƒCelsius. Carbon dioxide, the most prominent GHG, is formed primarily by the burning of the "fossil" fuels coal, oil and natural gas, and has increased from 315 ppmv (parts per million by volume) in 1958 to 392 ppmv in 2010. Methane global concentrations increased about 1% per year from 1.52 ppmv in 1980 but slowed down in the 1990s to a nearly constant 1.78 ppmv from 2000 to 2008, and is growing slowly now. Nitrous oxide is also steadily increasing in atmospheric concentration.
The chlorofluorocarbons (CCl2F2, CCl3F, etc.) are not only GHG contributors but also are suppliers of atomic chlorine in the strato- sphere, leading to substantial loss of ozone. Every September since the mid-1980s a rapid loss of ozone occurs in a few weeks over the south polar area, resulting in the formation of the well-known Antarctic Ozone Hole, which fades away in mid-spring. These losses in stratospheric ozone led in 1987 to the international adoption of the Montreal Protocol which banned the further manufacture and release of the chorofluorocarbon gases. This Protocol has now been in effect for 23 years, and has been very successful. Nevertheless, the Antarctic ozone loss will occur throughout the 21st century because of the long survival lifetimes of the CFCs. The increase in GHGs will warm the Earth much more in the 21st, Century unless controls for these GHG gases are rapidly put in place.