The IEA’s base case is that annual CO2 emissions will rise by a further 16pc by 2040, but it would be a radically different picture if world leaders grasp the nettle and agree on measures to stop CO2 in the atmosphere rising above 450 parts per million by the 2100. That would imply a 50pc cut in emissions over the next 25 years, and a steeply-rising carbon price. This will not happen in Paris but United Nations officials say such an accord is within grasp over the next five to 10 years.