I've been hearing for years about methane gases building in our atmosphere and becoming a serious problem. Methane is emitted every day, naturally. Always has been and always will be. Unless we eliminate natural gas (the stuff you use to heat water and cook); cows, goats and sheep (they belch it, fart it and those patties they drop emit it); landfills (where's all the kitchen refuse going then?), wetlands (aren't we fighting to protect those?) and rice paddies (got any idea how many folks depend on rice as a main part of their diet?).
If you like "studies," here's one for you. Ancient Roman and Chinese folks were producing "man made" methane long before the Industrial Revolution (that's when humans started building machines that produced air pollutants).
There weren't as many of them (folks) and they weren't as efficient or ingenious as we are today and their inventions weren't as sophisticated as ours, but they were beginning to produce some of the cause of "Global Warming."
Here's something else I found interesting -- ice core samples taken in Greenland are showing evidence of high methane emissions. If these samples are trapped in ice, doesn't that mean they were frozen over? If they were frozen over, does that mean Greenland wasn't always covered in ice? If Greenland wasn't always covered in ice and is now melting, doesn't that indicate a normal cycle of Nature?
Ice cores from just about every place I've ever thought of as frozen, have contained evidence of all kinds of flora and fauna. I always thought that meant some millennium things were froze up and some millennium they weren't.
I know "man" is putting a lot of stuff into the air that we'd all be better off without. I question whether it's the Gloom and Doom Scenario some would have us believe.