Greenhouse gas

A greenhouse gas (GHG) is a gas or vapor such as carbon dioxide, methane, or water vapor which contributes to global warming by absorbing infrared radiation coming from earth then re-radiating part of it back to earth. Water vapor and carbon dioxide account for most of this green house effect. The gas of greatest concern is carbon dioxide because humans have raised its concentration in the atmosphere greatly by the burning of fuels and the cutting down of forests. (Forests take carbon dioxide out of the atmosphere by photosynthesis when they are alive and release it into the atmosphere when they are killed and decompose or are burnt.) The concentration of carbon dioxide in the atmosphere prior to the industrial era was about 280 parts per million (ppm) by volume. Over the past 200 years humans have introduced about 400 petagrams (petagram = 1015g) of carbon into the atmosphere. Part of this has been taken out again by oceans and terrestrial vegetation, and part remains. The concentration of carbon dioxide in the atmosphere is now about 387 ppm (2010 figure). Most experts place the safe limit of carbon dioxide in the atmosphere somewhere between 350 and 550 ppm (although some outlying figures, maybe no longer current, are as high as 750 ppm). As of 2011, we were pumping nine petagrams of carbon into the atmoshere per year.

Life of pollutants in the atmosphere
and, soot, are relatively short lived in the atmosphere. Both offer opportunities for control which exceed those for carbon dioxide which is long-lived in the atmosphere. (According to the IPCC, `It is very likely that more than 20% of emitted CO2 will remain in the atmosphere longer than 1000 years after anthropogenic emissions have stopped.' ) Black carbon, soot from fires, power plants and engines, lasts only a few weeks. It plays a major role in the melting of Arctic and s which may result in. Methane often enters the atmosphere through pipeline leaks, which, if the effort is taken, can be sealed, saving both money and the atmosphere. Methane may also be flared, burned off.

Source
Intergovernmental Panel on Climate Change (IPCC), Climate Change 2013, Chapter 6, `Carbon and Other Biogeochemical Cycles' (a.k.a. `Working Group  I  contribution  to  the  IPCC  5th  Assessment Report "Climate Change 2013: The Physical Science Basis" ').