By Mark Brownstein The U.S. and the European Union announced a commitment today to cut their methane emissions 30% by the end of the decade, and are rallying other governments to join them. It’s the best climate news we’ve had in a long time, particularly after this summer’s global wave of extreme weather disasters. The pledge is a milestone in the climate fight, establishing a central place for methane in the race to achieve the warming limits in the Paris Climate Agreement. This vital role was sharply underscored last month by the Intergovernmental Panel on Climate Change. Cutting these emissions is the single best chance we have to slow the rate of warming, even as we decarbonize the energy system. The new methane pledge is a litmus test for any country coming into November’s United Nations climate talks . But it is also important to understand that a 30% methane cut represents a floor, not the ceiling — evidence is clear that even greater results are possible.…