Professor Sir David MacKay, who has died aged 48, was a Cambridge University physicist who set out to cut “UK emissions of twaddle” by applying the laws of physics and mathematics to the debate on sustainable energy.

His book, Sustainable Energy – Without the Hot Air (2009), provided a user-friendly guide to how much energy we consume in our daily lives, the lifestyle changes that would substantially reduce that total, and which kinds of technology would make a difference. Amusingly written, it was acclaimed as a breath of fresh air in the often self-righteous and highly charged atmosphere surrounding the debate about climate change, and led to his appointment in 2009 for a five-year term as chief scientific adviser to the Department of Energy and Climate Change.

In an interview with Leo Hickman in The Guardian, MacKay explained that he had decided to write the book because he was tired of the “greenwash” surrounding the energy and climate change issue: “I was tired of the debate – the extremism, the nimbyism, the hairshirt. We need a constructive conversation about energy, not a Punch and Judy show... I wanted to write a book about our energy options in a neutral, human-accessible form.”

MacKay’s book, published free on the internet before it appeared in the bookshops, was an immediate sell-out. Within two years it had sold more than 40,000 copies in print and been downloaded about 400,000 times. It also succeeded, against the odds, in winning accolades from all sides of the climate change debate, one commentator describing it as the “Freakonomics of climate change’’.

In fact the book was not primarily about climate, but as MacKay argued, even if some people do not care about climate change, with continued rapid depletion of North Sea oil and gas reserves (and because fossil fuels are a finite resource), a sharp reduction in Britain’s fossil-fuel consumption would seem a wise move if we care about security of supply.

MacKay’s genius was to express all forms of power consumption and production in a single unit of measurement – kilowatt hours per day (kWh/d). A 40 watt lightbulb, kept switched on all the time, uses one kWh/d, while driving the average car 50km a day consumes 40 kWh/d. Such comparisons, MacKay argued, help to shift the focus to the major issues away from much-hyped “eco-gestures” such as believing you have done your bit by remembering to switch off the mobile phone charger. “The amount of energy saved by switching off the phone charger is exactly the same as the energy used by driving an average car for one second,” he wrote. Switching it off for a year saves as much energy as is needed for one hot bath. Such gestures were akin to “bailing out the Titanic with a teaspoon”.