>"It's a more powerful greenhouse gas than carbon dioxide, and should be easier to control | Leaders"

That is important, and frightening, but hardly shocking. The aim of letting the world warm no more than 1.5°C, agreed on in Paris six years ago, is one to which many countries, notably the small-island states for which sea-level rise is an existential threat, are deeply committed. But many observers believe it stringent almost to the point of impossibility.