BBC: Leaders of G8 nations are to set a target to cut greenhouse gases by 80% by 2050, the BBC understands. They will also call for any human-induced temperature rise to be held below 2 degrees Celsius, says BBC environment analyst Roger Harrabin. But environmental campaigners believe key commitments will be scaled back. News of the G8 plans came as ex-Prime Minister Tony Blair urged rich nations to hit short-term climate targets by ramping up existing clean …