Greenhouse Gases

Here are some greenhouse gases we could use to terraform other planets/moons (via the greenhouse effect).

Carbon dioxide
Probably the most simple, common, and easy to produce of the known greenhouse gases, it has a very little global warming potential compared to other gases, but is extremely necessary to life on Earth.

Sulfur hexaflouride
According to the Intergovernmental Panel on Climate Change, SF6 is the most potent greenhouse gas that it has evaluated, with a global warming potential of 23,900 times that of CO2 when compared over a 100-year period. Measurements of SF6 show that its global average mixing ratio has increased by about 0.2 ppt per year to over 7 ppt. Sulfur hexafluoride is also extremely long-lived, is inert in the troposphere and stratosphere and has an estimated atmospheric lifetime of 800–3200 years. SF6 is very stable, but it could have some unforeseen risks.

Perfluorocarbons
Perfluorocarbons such as Tetrafluoromethane (CF4) and Hexafluoroethane (C2F6) are very powerful greenhouse gases, thousands of times more effective than CO2.

CF4 has the longest atmospheric lifetime of 50,000 years and does not deplete the ozone layer. Though relatively stable, it reacts explosively with alkali metals and produces toxic gases when combusted, and can cause heart problems with long term exposure.

Methane (CH4)
It has 72 times the global warming potential of CO2 (over 20 years), but this number degrades to 25 times after 100 years and 7.6 times in 500 years. This is because natural processes in the atmosphere breakdown methane into carbon dioxide and water vapor (though both of these are also greenhouse gases). Methane is also flammable.

Chlorofluorocarbons
Chlorofluorocarbons like CFC-12 and HCFC-22 are amoung the most powerful greehouse gases, but because most easily destroy ozone layers, using them would not be practical in most terraformed atmospheres.

Other gases
Nitrous oxide (N2O) is a lot stronger than carbon dioxide, but causes noticable neurological effects in high concentration (this gas is also known as "laughing gas").

Nitrogen triflouride (NF3) is very stable gas with a global warming potential 17,200 times greater than that of CO2.

Water vapor is very common in Earth's atmosphere (up to 3% by volume), and is the gaseous state of water. It maintains the all-important water cycle, and would need to be present in large quantaties on other worlds as well.