I think the title says it all...
closed as too broad by Jan Doggen, arkaia, Fred, Semidiurnal Simon, John Oct 7 at 19:55
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Yes, you are right, the title says it all. The presence of greenhouse gases, of which there are several, allows radiant energy from the sun to pass through the atmosphere but hinders the longer wavelength, infra red, thermal radiation from getting back out again, thus acting like the glass in a greenhouse. CO2 is a less effective greenhouse gas than methane, but there is much more of it in the atmosphere and it stays there longer, so this is the one which causes most concern. There are natural processes which reduce the amount of CO2 and methane in the atmosphere as long as the input, mainly from human activity, is not more than they can deal with.