Illustrated implications of the Terrifying New Math of Meinshausen and McKibben

There is a limit to the quantity of greenhouse gases that may be emitted to the atmosphere if catastrophic climate change is to be avoided. The practical implication is that most of the world's fossil fuel inventory must be left in the ground and not burned. The article analyses the implications of adhering to the carbon budget in terms of the implied rate of reduction in emission intensity of the world economy. The world economy must be decarbonised by 2050. The four major emitting countries are examined for their energy and emission policies, their emissions and the trajectories of their required emission intensities derived. This shows how sharply emission intensities will need to be reduced when present policies expire, particularly in Russia and China. The postponement to concerted international action to 2020 increases the costs of action. But barriers to a comprehensive international agreement on limiting emissions still exist. It seems likely that countries will continue to be free to pursue policies for the maintenance of economic growth as a priority. The cost of renewable energy, particularly solar, continues to fall. The market, rather than regulation, may transpire to be the main driver of decarbonisation.