The world is coming to an end! In around a billion years’ time. The news is expected to lower house prices, in another blow to beleaguered homeowners.
It’s nothing you didn’t already know, really: the Sun, following the so-called Main Sequence, the life cycle of stars, will eventually begin to swell and grow hotter. Eventually, the Earth will, basically, cook; the seas will boil, the forests (if there are still forests) will burn, any surviving animal life will be chargrilled.
The new information is that multicellular life might not make it that long. In a billion years or so, according to astrobiologists at the University of St Andrews, the increasing temperatures will strip carbon dioxide from the atmosphere, meaning that photosynthesis will cease, plants will die, and all the animals that rely on plants – that is, all animals, really – will starve. Then temperatures will continue to rise, the waters will boil, and all but the toughest microbes will die too.
You don’t need to worry about this all that much. You’ll be dead in about 0.000002 per cent of the time remaining to multicellular life, give or take an order of magnitude. Humanity has, so far, been physically modern for about 250,000 years, or about one-4000th of that time. The most ancient individuals we know of – probably the Egyptian “Scorpion Kings” of the pre-dynastic period – lived about 5,000 years ago, or about one-200,000th of the time between now and the big boiling. Finding out that humanity only has a meagre billion years of planet-time left is very unlikely to cramp our style.
Which is not to say, of course, that we have nothing to worry about. The computational scientist Stephen Emmott took to the pages of The Observer the other day to warn of the impending doom that faces us as the planet fills up with people (he’s written a book called “Ten Billion”, if that gives you an idea). We are going to run out of water, poison the atmosphere, and starve. (Another worrying post on the Washington Post’s WonkBlog shows food yields growing steadily, but populations growing faster, in apparent vindication of the great early economist Thomas Malthus’s doom-laden prophecies.)
These potential apocalypses, of course, face us a few million times quicker than death by solar expansion. But, unlike the Great Boiling, these predictions say more about the people predicting than the world itself. As I’ve written before, in the 1960s various people predicted with the utmost confidence that most of the world would be starving by 1980, but in fact food yields have gone up by 25 per cent per capita despite the population doubling in that time. In the 1920s and 1930s people were worried about underpopulation, not overpopulation. At the moment, demographic predictions seem to suggest a global population peaking between 9 and 10 billion in the second half of this century, but demographic predictions are probabilistic things: the “95 per cent confidence interval” for 2100AD, ie the region that the forecasters are 95 per cent sure that the real figure will end up in, is between 6.2 billion and 15 billion. That is, the population could double, or it could fall. Confident predictions of 10 billion, or anything else, are little more than guesses.
Annoyingly, humans are complex things, which have a tendency to adjust their behaviour in unpredictable ways – including in response to predictions of their behaviour. We’re also very good at solving problems, or mitigating their effects, and generally carrying on. We also tend to have fewer children when we are more educated, and when we live in safer times – which is good news for those afraid of overpopulation, because the world is getting safer and people are getting more educated. There is the concern that we’re changing the atmosphere, but if I were a betting man I’d say that we’re ingenious enough to avoid the worst of the problems that causes as well (although the Tragedy of the Commons does make that a particularly difficult one). Doomy predictions that we’re all going to starve have been going on for a couple of hundred years now; that’s not to say they’re wrong this time, but it does mean we should be careful about taking them at face value.
On the other hand, stars are fairly predictable things. In about five and a half billion years, after the Andromeda galaxy collides with ours, the Sun will reach the end of the Main Sequence and become a red giant; a couple of billion years after that, it will swallow the inner planets of the solar system, possibly including Earth, and that really will be the end of that. It’s a lot further away, but it’s a lot easier to predict. Overpopulation will not be the main problem by then.