Methane is a long-lived gas in the atmosphere, very difficult to destroy. It was thought to be mainly due to natural sources, swamps and things like that. To my surprise I found that methane's contribution to water vapor is about as large as that feared to come from a hypothetical SST fleet. Public interest in methane theory was mild, to say the least. It was finally published in 1971 in the British journal Nature .
Cows are so natural and low-tech.
Not a great cause. And besides, controlling their emissions could be messy. And now CFCs Chloroflourocarbons, or CFCs, are different. Brilliant work by a British scientist, James Lovelock, and the calculations of two Californians, Mario Molina and Sherwood Rowland, demonstrated in 1974 the possibility that long-lived and normally quite inactive CFCs would percolate up into the stratosphere, and there be decomposed and attack ozone. Environmental activists were ecstatic.