T o start with health professionals paid little attention. After all, it was an environmental issue and their core business was health. But the burning of fossil fuels was increasing the concentration of carbon dioxide in the atmosphere to alarming levels. This was rapidly changing the earth's climate, threatening the balance of the biosphere with serious implications for human health (Lancet (2002);360: 1347-60 and BMJ 1999;318: 1682-5).

The stakes could not have been higher. Reducing carbon dioxide emissions required global, national, and personal commitments to reduce fossil fuel energy use. Governments would not implement the necessary measures without public support, but personal carbon rationing required a carbon literate society and radical changes in lifestyles.

Societal changes of this magnitude required …