Strangely, methane emissions and atmospheric levels are dropping even while other greenhouse gases escalate. We're not sure why. But most of us in agriculture have long since tired of newsreaders' staged amusement when reporting that ruminant animals are a major source of methane. (snicker)
The decline may be due to changes in rice farming:
There are likely other reasons as well. Regardless, lower methane levels would contribute to mitigating global warming as well as air pollution.
M. Aslam Khalil, a physicist at Portland State University in Oregon, helped establish a sampling network for methane as long ago as 1979. He, like Dlugokencky, believes that the recent stasis in methane levels fundamentally represents the system coming to equilibrium. Khalil suspects that there have been no significant changes in the overall magnitude of emissions, but he does recognize that some of the individual sources must have become larger over the past few decades. The explanation for the enigmatic stabilization of methane levels, in his view, is that at least one of the other sources—rice agriculture in particular—has simultaneously become much smaller.
In a paper soon to be published in Greenhouse Gases and Animal Agriculture: An Update (Proceedings of the 2nd International Conference on Greenhouse Gases and Animal Agriculture), Khalil and his Portland State colleague Martha J. Shearer point out that China has produced much of the world's rice for many decades, yet for the past 30 years, the area devoted to rice agriculture in that country has fallen from about 37 million hectares to a little more than 27 million. Khalil and Shearer further note that in these rice paddies nitrogen-based fertilizer has to a large extent replaced animal manure or "night soil" (human wastes). This change in how rice is grown in China reduces the amount of methane given off. What is more, these rice farmers are using less water than they did before—another change in agricultural practice that has the unintended side benefit of reducing methane emissions. [More]
Oddly too, natural gas production is a larger source of methane emissions than cows. But I have not heard much about restricting NG production like we have with livestock.
Maybe the jokes were just not as funny...