Nearly a dozen deep-pocketed philanthropies announced on Saturday they will invest $450 million over the next three years to help countries launch national actions to tackle methane, the second-most prominent greenhouse gas, which has become a new focus of global climate negotiations. The philanthropies, which include the Bezos Earth Fund, Bloomberg Philanthropies and the Sequoia Climate Foundation, will help accelerate the phase-down of methane emissions and other non-carbon dioxide greenhouse gases.