<p>Natural gas, composed mostly of methane, is considered the most climate-friendly of the three main fossil fuels, with only about half the carbon dioxide emissions of coal. But methane is itself a powerful greenhouse gas, particularly on shorter timescales. Leaks of methane during natural gas production, transportation and use threaten to weaken or even eliminate its climate advantage, and some environmental groups have seized on the issue to oppose natural gas developments. How serious is the leakage problem? And how can companies address it?</p>

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