Wolfram/Alpha provides information on the relative global warming effects of about 30 common pollutants in the atmosphere using the global warming potential (GWP) index.
The GWP index estimates how much a certain chemical will add to global warming compared to the same mass of carbon dioxide over a certain time span. Here’s an example with methane: Choose timeframes of 20 years, 100 years, and 500 years to see the short-term and long-term contributions of methane in the atmosphere. You’ll see that the longer the timeframe, the GWP decreases. This may seem counterintuitive, but makes sense when you discover that methane has an atmospheric lifetime of about 12 years. As a next step, compare methane to other greenhouse gases in the short and long term.