While less than half of the warming in the next 20 years will be caused by CO2, other gases such as methane, and black carbon particles (soot) will have the greatest effect.
According to Professor Kirk Smith, writing in the New Scientist Magazine:
“Less than half of the total warming expected over the next 20 years will be caused by CO2. Methane, along with other gases such as carbon monoxide, volatile organic compounds (VOCs) and black carbon particles, will cause most of the changes.”
Date: 25 June 2009
Source: Global warming in the twenty-first century: An alternative scenario NASA site – abbreviated version – Proceedings of the National Academy of Sciences (PNAS) – full article