How, as a prosperous westerner, do you free yourself from the guilty knowledge that your bequest to planet earth will be a hotter and less hospitable climate? In the hours between breakfast and lunch, Britons and Americans are responsible for more carbon emissions than someone living in India is likely to produce in an entire day. European governments hope to reduce this deadly toll by offering big subsidies for measures that will lessen our dependence on fossil fuels. Billions have been spent, yet progress is slow.

For more than two decades I have been helping utility companies around the worldmake electricity generation cleaner. For most of that time, however, my personal environmental credentials have been a muddier shade of green. The guilt began at home (a draughty 19th-century house heated by oil, one of the dirtiest-burning fuels) and it followed me everywhere I went in my petrol-guzzling car. Heating homes and getting around accounts for more than half of the energy used in Britain. Spurred on by my wife, our family asked ourselves: how little could we use?

Our first step was choosing a sustainable form of heating. My wife was keen on subsidised solar panels, but I could not in good conscience spend thousands of taxpayers’ pounds pointing photovoltaic cells at London’s gloomy skies. Instead we chose two air-source heat pumps to provide heat and hot water.