In the 19th century, cholera outbreaks that escaped from the slums to kill rich and poor alike caused the great Victorian revolution in public health. Fear of cholera ensured that vast sums were spent on building sewers and ensuring that everyone had clean water. Climate change is the cholera of our era — fear of the havoc that climate change will wreak should stimulate a new public health revolution. And just as doctors led the Victorian campaign, so the medical profession should be in the vanguard of this new revolution in public health.

The front page of The Lancet of May 16 says it all: “Climate change is the biggest global health threat of the 21st century.” This prestigious journal, which usually gives no more than ten pages to vitally important clinical research, made space for a 39-page report.

Climate change will hit the poorest nations hardest, but it will affect us too. In the summer of 2003, la canicule, an unexpected heatwave, killed 14,000 elderly people in France. Rising temperatures will bring that type of problem to our shores. Our health services will be put under pressure by severe weather and floods. But it is the global effects that will hit us, and especially our children and grandchildren, because of the effect that climate change will have on world food and water supplies; millions of climate refugees will disrupt the borders of even an island nation.

Smoking, Aids, swine flu? They all pale into insignificance compared to climate change’s threat to health. That proposition will instantly provoke a hostile reaction from the diminishing band of climate-change sceptics. But as a doctor of 40 years’ standing who has been involved in running public health services for 30 years, I know that the evidence is good enough to make action, not inaction, the sensible choice. An empirical view of the data shows that delay will not just increase the amount of preventable harm, it may take us past a point of no return.

So the medical profession must accept responsibility in the campaign for change. However, with a few notable exceptions, doctors are effectively silent on the health threat that will come to define our age. My fellow doctors cannot just leave this issue to their leaders, to the presidents of the Royal Colleges and to the members of the Climate and Health Council. They should be active in their local communities, where they are known and respected, using their influence to press for national and international action.

Leaders, no matter how great, must have courage and a mandate to act. What is needed, for instance, is for 20 or 30 MPs to collar Ed Miliband, the Climate Change Secretary, as he rushes across the lobby and say: “Three [or more] doctors have been to my surgery in the last month warning me about the concern that they and their patients have about climate change — that’s more doctors than have ever come to see me about the NHS or even their pay. They tell me the medical profession is clear what needs to be done.”

“Why do I never get letters from doctors about smoking?” an MP asked me when I was the secretary of Action on Smoking and Health. “Why do I get more letters on animal welfare than human health?” Why indeed. The medical profession is too silent, and sometimes too apathetic. Fortunately, many of today’s medical students and young doctors have fire in their bellies and are taking to the streets demanding action. Their older colleagues should join them and use their influence. Perhaps, they could try some “collar-and-tie” direct action — those doctors who own shares should be at AGMs demanding that companies clean up their environmental acts.

But the medical profession needs to put its own house in order too. I was in a hospital last month that is doubling its electricity supply “to meet demand”, with no thought about the future. Sometimes the NHS is not unlike Dickens’s Mrs Jellyby, keen to reform others while her own children were scalded through neglect.

The NHS is gigantic and has a carbon footprint that is nearly one twentieth of the whole UK’s footprint — 1.3 million staff each with their own footprint, the drugs bought, the buildings, the transport, the water and the food, too much of it thrown away. Now is the time for the profession to mobilise and show the passion that took them into medical school but is then so often extinguished.

In December in Copenhagen, the vital United Nations Climate Change Conference meets. Unfortunately, British MPs are distracted, so the medical profession has a duty to act to make the politicians focus on it.

A recent summit meeting of leading doctors at the British Medical Association unanimously agreed that the need for action is essential. However, battles are not won in headquarters but by the troops on the front line. So I would like to see 90 per cent of doctors making environmentally friendly personal changes; half of doctors signing the Climate and Health Council pledge; and at least one in 20 doctors lobbying their MPs face-to-face. What more appropriate place than a constituency surgery could there be for a doctor to tell his or her MP that the medical profession thinks that urgent treatment is needed?

Professor Sir Muir Gray is Public Health Director of the Campaign for Greener Healthcare

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