Climate forcings are those parts of the climate system which push it along. CO2 does it. It is, because of how much of it there is and how long it stays in the atmosphere, the most important climate forcing, and the most significant cause of today’s present warming trend. But it’s not the only greenhouse gas or the only force affecting the climate. Other greenhouse gases contribute. Deforestation and agricultural practices contribute. Warming causes more water to evaporate, and since water vapour is itself an important greenhouse gas, that contributes as well. Aerosols and major volcanic eruptions can mitigate the effect. Positive feedback mechanisms like that associated with Arctic sea ice melting can make the effect worse.
The following video from the National Academy of Sciences, the fifth in the series about climate change, discusses the issue of climate forcings.
The first four videos can be found here:
1. What is climate? https://fathertheo.wordpress.com/2012/10/12/what-is-climate-video/
2. Is Earth warming? https://fathertheo.wordpress.com/2012/10/13/is-earth-warming-video/
All of the videos can be found at the National Academy of Sciences special website here: http://nas-sites.org/americasclimatechoices/videos-multimedia/climate-change-lines-of-evidence-videos/