This is a complex issue. I believe heartily in global warming and have concerns over the environment. The primary cause is the greenhouse effect. The most important greenhouse gases are carbon dioxide, methane, nitrous oxide and water vapor. While all these gases occur naturally in the atmosphere, emissions from human sources has caused their levels to rise to a point that is no longer sustainable.
While carbon dioxide accounts for 72% of greenhouse gases, methane has a shorter lifespan, and consequently, is not as abundant in the atmosphere as in terms of its effect-- BUT, it is much more potent.
Agricultural products appears to account for 12.5% of the emissions. Methane gas alone is 18% of the total because not only livestock produce methane gas as waste. Before the industrial revolution, there were as many as 60 million bison roaming the Great Plains compared to 98.4 million cows in the US today. Bison farted happily to their heart's content before the 1800s and some people argue that it did not contribute to significant emissions. But there are more people, animals, decomposing organic matter and natural gas extraction than in previous eras. Animal rights groups argue the reverse, but the big picture arises when all the various sources are considered.
Animal rights activists have compassion for animals, are not scientists nor environmentalists. To me, this is what makes it a political issue rather than a scientific one. And science should have the loudest voice, despite some legitimate beefs (pardon the pun) from each particular group.
It is just not that cut and dried, not that simple, no matter whose point-of-view is considered.
http://globalwarming-facts.info/causes- ... ing-human/
https://www.quora.com/How-many-cows-are-there-in-the-US
https://en.wikipedia.org/wiki/American_bison
