Day two of the COP26 conference saw an ambitious promise to tackle one of the biggest contributors to global warming. Six of the world’s 10 biggest methane emitters pledged to cut methane emissions by 30% by the end of this decade. But as Jaime Ocon reports, they failed to get commitments from Australia, China, Russia and India, leading to questions about whether the deal will have a real impact, or whether it's all just hot air.