Methane is the second-largest contributor to global warming after carbon dioxide. But new and better techniques to spot major emitters of the odorless, colorless gas have pushed curbing it up climate to-do lists. Scientists view reducing methane emissions from the fossil fuel industry as the cheapest and easiest way to hold down global temperatures in the near term. That could counterbalance the initial warming effect from declining use of dirty fuels -- which also pump out fine particles that r