BBC: Official advisers to the UK government have demanded Britain slash greenhouse gases by a fifth of current levels by 2020 – the toughest target so far. The Committee on Climate Change said a cut of 21% on 2005 levels was needed for the UK to play its fair share in combating dangerous change. It proposes firm carbon budgets for the next three five-year periods. It is believed to be the first time any major nation has attempted such a move. Ministers are considering the …