Can civilisation prolong its life until the end of this century? “It depends on what we are prepared to do.” He fears it will be a long time before we take proportionate action to stop climatic calamity. “Standing in the way is capitalism. Can you imagine the global airline industry being dismantled when hundreds of new runways are being built right now all over the world? It’s almost as if we’re deliberately attempting to defy nature. We’re doing the reverse of what we should be doing, with everybody’s silent acquiescence, and nobody’s batting an eyelid.”

Hillman is amazed that our thinking rarely stretches beyond 2100. “This is what I find so extraordinary when scientists warn that the temperature could rise to 5C or 8C. What, and stop there? What legacies are we leaving for future generations? In the early 21st century, we did as good as nothing in response to climate change. Our children and grandchildren are going to be extraordinarily critical.”

Although Hillman has not flown for more than 20 years as part of a personal commitment to reducing carbon emissions, he is now scornful of individual action which he describes as “as good as futile”. By the same logic, says Hillman, national action is also irrelevant “because Britain’s contribution is minute. Even if the government were to go to zero carbon it would make almost no difference.” Instead, says Hillman, the world’s population must globally move to zero emissions across agriculture, air travel, shipping, heating homes – every aspect of our economy – and reduce our human population too. Can it be done without a collapse of civilisation? “I don’t think so,” says Hillman. “Can you see everyone in a democracy volunteering to give up flying? Can you see the majority of the population becoming vegan? Can you see the majority agreeing to restrict the size of their families?”

Hillman accuses all kinds of leaders – from religious leaders to scientists to politicians – of failing to honestly discuss what we must do to move to zero-carbon emissions. “I don’t think they can because society isn’t organised to enable them to do so. Political parties’ focus is on jobs and GDP, depending on the burning of fossil fuels.”