For something of us to survive in the millennia or even aeons ahead we will have to dodge some bullets. To date, the most plausible agent of doom after all the dozens that have been postulated (asteroid strikes, GM plagues, climate catastrophes and so forth) is and will remain a global nuclear war. Nothing else so tangible and so immediate has the capability to kill billions of human beings in a short time. Despite arms treaties there remain more than enough nuclear weapons to do terrible damage. It is perhaps surprising that while millions live in a state of feverish panic about climate change, the continuing and far more substantial threat of atomic destruction appears to have receded from our collective consciousness.

But even this, even the most terrifying existential threat we face, would probably not be the end of our species. An all-out war, such as the one we pondered a generation ago when the arsenals of Nato and the USSR were at their height, would have killed perhaps 3bn people. But even after this most ghastly of cataclysms there would have been billions of survivors, and in a century or two something approaching modern civilisation would probably have re-emerged.

After the bombing of Hiroshima and Nagasaki in 1945, it was popularly assumed that the two cities would remain uninhabitable until the early 21st century. In fact, both were rebuilt within a decade. The feared birth defects never materi­al­ised in any numbers and, generally, the effects of radiation were rather overstated, as they still are today (the myth that Chernobyl killed tens of thousands of people is remarkably persistent).

Now a new monster lurks under the bed: climate change. Until very recently it was perfectly proper to be sceptical about ­global warming. Much of the science was speculative; much of the fervour quasi-­religious. Now the figures are in and denial is no longer viable.