ClimateWire: When it comes to fighting climate change, pick a number — any number. Nearly 200 countries have signed a U.N. treaty pledging to avoid “dangerous” climate change. But lately, it seems, “dangerous” is lost in translation. Fifteen years since that agreement took effect, scientists and governments are still grappling with what carrying out its promise means. For the European Union, it means limiting Earth’s warming to just 2 degrees Celsius hotter by the end of this century than …