While carbon dioxide and methane are the best known greenhouse gases, they are not alone in contributing to global warming. Nitrous oxide and the halocarbon gases are also powerful traps of long-wave heat energy emitted by Earth.
Nitrous oxide (N20), better known as laughing gas, plays an important role in the chemistry of life. Although scarce in the atmosphere, with a mean concentration of just 311 parts per billion (a thousand times less abundant that carbon dioxide), a molecule of nitrous oxide is some 200 to 300 times more effective as a greenhouse gas than a molecule of carbon dioxide. Furthermore, it is longer lived, typically lasting some 150 years in the air. These two facts make nitrous oxide a dangerous greenhouse gas, one that has increased by approximately 9% in the atmosphere since the Industrial Revolution.
The halocarbons are man-made compounds of carbon which combine with one or more of the five elements called halogens: fluorine, chlorine, bromine iodine and astatine. The most common are the CFCs (chlorofluorocarbons) and the HCFCs (hydrochloroflurocarbons). CFCs are particularly effective greenhouse gases, being between 3000 and 13,000 times more powerful at global warming than carbon dioxide. The abundance of CFCs in the atmosphere before the 1950s was practically zero. However, during the 1960s and 1970s, they escaped into the atmosphere from millions of scrapped refrigerators, where the gas was used as a coolant. CFC production was controlled in the 1980s and 1990s, owing to their destructive effect on the ozone layer, which protects us from harmful ultraviolet radiation. And so their contribution to global warming is expected to decline rapidly over the coming decades.