What needs to be done? Adaptation is part of the answer, partly because further warming is certain, given the concentrations of greenhouse gases already in the atmosphere. But mitigation must also be central. Fortunately, many of the technologies needed to lower greenhouse gas emissions per unit of output are known already. What also emerges from the analysis is that there is no dominant solution. A mixture of technologies will be needed, instead (see chart). Among them are: increases in efficiency; carbon capture and storage; nuclear power; use of biofuels; and domestic combined heat and power. Also important, however, is forestation.

　　How are such shifts to be brought about? The broad answer is through a combination of pricing of greenhouse gas emissions, investment in new technologies and regulation of energy efficiency.

　　This raises the biggest question of all: how is humanity to deal with what is both the biggest “market failure” ever seen and an unprecedented challenge to its capacity for large-scale and enduring co-operation. Is it imaginable that the countries of the world, with their vastly different views and interests, will rise to the collective action challenge climate change poses?

　　Hitherto, the answer to that question has been a resounding “no”. The report may have made a case for early action. But it could easily end up as just another futile exhortation. Whether that has to be so is the question I plan to address next week.