In carbon trading mechanisms, the global warming impact of other gases (e.g. methane and nitrous oxide) are expressed in terms of CO2 equivalents.

The conversion factors are: 25 for CH4 and 298 for N2O (over 100-year time span).

This means that the impact of 1 kg of CH4 is similar to 25 kg CO2 equivalents and the impact of 1 kg of N2O is similar to 298 kg of CO2 equivalents over 100-year time span.

Dear Nitin,

until very recently, methane was seen as something of which you can reduce the emission by human measures (in rice for example by intermittent irrigation or composting of material ploughed under) but you can' t have it absorbed somewhere, while carbon dioxide has many sources as well as many sinks.

This picture is so complex that we cannot calculate easily the life time (or half life) of a carbon dioxide molecule in the atmosphere as we can do it for a methane molecule, that is chemically destroyed. So trading methane makes no sense, only rewarding the reduction of its emission, while trading CO2 makes sense  due to the ways we can influence its presence in the atmosphere

Very recent research would have shown that for example Christmas trees do absorb methane. In that case the picture for methane could change.

Best wishes, Kees   

They did a lot. Methane emission from enteric fermentation and manure management is one of the environmental problems and also considered in several environmental initiatives including climate change mitigation. Nitrous oxide is also a case in point and has higher global warming potential than CO2. However, their concentration in PPB as compared to PPM for CO2 and that is why more attention is given to CO2 than CH4 and N2O form both national and global perspectives. For that matter water vapor is the most potent GHG but no one is taking about it because it natural.