Non-fossil methane

Although fossil natural gas is an important source of greenhouse gases, emitting 40−50 million tonnes per year, virtually all anthropogenic, it is not the largest source of methane, either natural or man-made. The following table are estimates of annual emissions of methane from various sources, in millions of tonnes.

Source	Natural	Man-made
Natural Wetlands	100-200
Rice paddies		25-170
Ruminants	45-80	25-40
Fossil NG		40-50
Biomass burning	10-30	10-50
Termites	10-100
Landfills & compost		20-70

Obviously, the ranges for some of these sources are very high, but if we add up the means for each, we get the following situation:

	Natural	Man-made
Mean	288	250

It is therefore clear that man is contributing nearly as much as nature. In fact, he is emitting more than nature because he has reduced the emissions from natural wetlands by marsh drainage. This is evidenced by the fact that the methane content of the atmosphere has increased 225 per cent, from 800 ppbv (1850) to 1800 ppbv (2000). It is evident that this increase is due to human activities, such as increased areas of rice farming, increased cattle farming and, of course, using fossil-fuel NG. This makes a significant difference to climate-change.