In four decades of climate negotiations, the world has focused intensely and exclusively on the most abundant climate-warming gas: carbon dioxide.

This year, scientists are urging a focus on another potent greenhouse gas — methane — as the planet's best hope for staving off catastrophic global warming.

Countries must make "strong, rapid and sustained reductions" in methane emissions in addition to slashing carbon dioxide emissions, scientists warn in a landmark report by the U.N. Intergovernmental Panel on Climate Change released Monday.