Bryan T. Pagel, a dairy farmer, watched as a glistening slurry of cow manure disappeared down a culvert. If recycling the waste on his family’s farm would help to save the world, he was happy to go along. But back, machinery was breaking down the manure and capturing a byproduct called methane, a potent greenhouse gas. A huge Caterpillar engine roared as it burned the methane to generate electricity, keeping it out of the atmosphere.