Last week was the hundredth anniversary of the Tunguska explosion.  If you weren’t celebrating, you should have been.  The incident was probably the nearest we have come to extinction in modern human history – and we survived.

A large object – presumably an asteroid or meteorite – collided with the earth.  If it had landed in Manhattan, it would have destroyed New York.  A bit bigger, and it would have been calamitous wherever it landed. A similar event at Yucatan, sixty-five million years ago, wiped out the dinosaurs and most other species.  It had been so with us had we been there.  We survived Tunguska because the impact was not too large, and Siberia.  There was only one known human fatality.

There are many catastrophes graver than meltdown in the markets.  The road to oblivion has many branches and unexpected turnings.  Environmental catastrophes, like meteorites or seismic events might do us in.  Something even more devastating than the Yucatan object is on its way, but it may be tens of millions of years before it reaches us.  Two hundred million years before Yucatan the Permian extinction was even more devastating.  We do not know the cause.  It might have been a meteorite, but another theory blames on the clathrate gun, a massive release of methane from the ocean floor.  Global warming could cause large methane release from permafrost or trigger another shot from the clathrate gun. But the environmental damage that humans cause is modest relative to the damage that the environment sometimes imposes on itself.

Many other potential apocalypses are of our own making. The Frankenstein problem of technology run amok is beloved by science fiction writers.  The world might be taken over by man-made objects, like robots, or mutations, like triffids.  It might be submerged in grey goo from nanotechnology.  The fiction genre survives because no-one can say categorically that any of these things are impossible.

Madmen have always been a threat to humanity, and technological advance increases their capacity to do damage.  Three individuals – Hitler, Stalin and Mao – bear direct responsibility for the deaths of thirty million or more people.  Hitler might have destroyed the world if he had the means

The influenza pandemic of 1918-9 was, with AIDS, the most devastating plague of modern times.  But the Black Death killed 30% of Europe’s population.  Still, 70% of our ancestors survived and therefore we do also.  We might not always be so lucky. A mutant virus might wipe out humankind and leave the world to less sociable species.  The spread of the Black Death across Europe took several years, but airlines could today carry the disease everywhere within hours.

Martin Rees, who engages with a litany of catastrophes, gave his book the provocative title of Our Final Century?   But while technology causes many problems, it also fixes many.  The Black Death was probably bubonic plague, and if so we could now cure it.  Even the asteroid can be deflected if we see it coming.

It is difficult to think about these issues in a dispassionate way.  In his book Catastrophes, Richard Posner – an American legal scholar who loves economics more than most economists – proposes a cost benefit analysis of all possible disasters.  But the attempts to model the end of the world are mostly bogus.  We have good data on frequencies of near earth objects, but there is no meaningful way to attach probabilities to these other calamities.

The best way of dealing with grave uncertainties, as with more banal disasters, is to buy options against them.  For each potential catastrophe, we should undertake research to ascertain what we might do if a remote possibility because a plausible reality. Instead we talk endlessly about less dangerous issues which give more scope for moral and political posturing.  Speeches about man-made environmental damage and world terrorism arouse audiences, but asteroids and grey goo only a chuckle.  Our actions against more catastrophic threats are few, ineffectual, and sometimes counterproductive.  In the meantime, mark 1 February 2019 and 13 April 2029 in your diaries.  These are the next dates on which a very large object from space might land on your head.