KATE ABNETT EUROPEAN Union policymakers have unveiled their most ambitious plan yet to tackle climate change, aiming to turn green goals into concrete action this decade and set an example for the world's other big economies to follow. The European Commission, the EU executive body, set out in painstaking detail how the bloc's 27 countries can meet their collective goal to reduce net greenhouse gas emissions by 55% from 1990 levels by 2030 - a step towards "net zero" emissions by 2050. This will mean raising the cost of emitting carbon for heating, transport and manufacturing, taxing high-carbon aviation fuel and…