Why might Methane be considered a more important greenhouse gas then Carbon Dioxide?
Higher green-house potential
Methane, if compered with carbon dioxide has about 30 fold more heat-trapping potential. On the other hand its lifetime in the atmosphere is of about ten years compared with about 100 years of carbon dioxide.
This means that methane has a greater green-house effect than carbon dioxide but only in short terms.
The issue is that the global warming is affecting the geo-biological cycle of methane. The main source of methane is from microbial activity in freshwater marshlands and this is boosted by a warmer climate.
Recent studies (published on the scientific journal Nature) show a clear increase in methane emissions from wetlands and a strong correlation of the magnitude of such emissions with temperature.
Another source of methane is from the melting of the permafrost (a layer of ice below the soil surface in sub-polar regions) that is increasing due to higher temperatures.
Overall methane impact on global warming is increasing and it is possible that this gas will become a more important greenhouse gas than carbon dioxide in the near future.