A Cool Calculus of Global Warming

The British government recently issued the most comprehensive study to date of the economic costs and risks of global warming, and of measures that might reduce greenhouse gas emissions, in the hope of averting some of the direst consequences. Written under the leadership of Sir Nicholas Stern of the London School of Economics, who succeeded me as Chief Economist of the World Bank, the report makes clear that the question is no longer whether we can afford to do anything about global warming, but whether we can afford not to.

The report proposes an agenda whose cost would be equivalent to just 1% of annual consumption, but would save the world risk equivalent costs that are five times greater. The reported costs of global warming are higher than in earlier studies because it takes into account the mounting evidence that the process of global warming is highly complex and non-linear, with a non-negligible chance that it may proceed much faster than had previously been thought and that the extent of warming may be much greater than had previously been thought.

Indeed, the study may actually significantly underestimate the costs: for instance, climate change may lead to more weather variability, a possible disappearance or major shift of the Gulf Stream – of particular concern to Europe – and a flourishing of disease.

When I served in 1995 on the Intergovernmental Panel on Climate Change, the scientific group that periodically assesses the science of global warming, there was overwhelming evidence that the concentration of greenhouse gases in the atmosphere had increased markedly since the beginning of the industrial revolution, that human activity had contributed significantly to those increases, and that they would have profound effects on climate and sea levels. But few saw, for instance, the Artic ice cap melting as rapidly as now seems to be the case.