As always, we sentient beings on earth are at risk of being wiped out by some global catastrophe. Some of the risks – diseases or meteorites – are old; others – nuclear weapons or global warming – are more recent. They are discussed very well in Nick Bostrom and Milan Cirkovic’s edited collection Global Catastrophic Risks:
In one sense, a catastrophe is just major systematic change. It needn’t be bad. But of course many people believe that the ending of sentient life on this planet would be a catastrophe in the evaluative sense. It would be very bad for most of the sentient beings living at the time of the catastrophe, and bad in some more impersonal sense since it would prevent many potential sentient beings from becoming actual.
Clearly the ending of sentient life isn’t the worst outcome imaginable. That would involve the existence of sentient beings, in great agony. But the question remains whether this kind of catastrophe would be worse than its not happening, with things continuing much as they are.
It’s at least arguable that it would not be worse. Most would accept that it could be good for some individuals – perhaps those with only a short time of intense agony left. But they would also think that the overall suffering in the world is counterbalanced by the good things in the lives of sentient beings, considered as a whole.
This seems very plausible as a claim about the lives of some such beings. But some individuals have lives of an extremely low quality, consisting sometimes of nothing much more than great agony over a fairly protracted period. How are we to weigh the value of all these different lives against one another?
In his An Analysis of Knowledge and Valuation (1946), the American philosopher C.I. Lewis suggested that we might attempt such comparisons by imagining that we ourselves have to live the lives of all those concerned, in series. It might seem that such a comparison relies on some controversial theory of personal identity. But it need not. Imagine that by some means your own life could be extended hugely, and that you would then be plugged into some machine that would ‘play back’ into your consciousness all the experiences of all sentient beings until there were no more left.
Of course, many of these experiences would be wonderful. But many of them would be very bad indeed. It’s not clear to me that this stream of experiences would overall be better for me than no experiences at all, since the amount of suffering would be so great that perhaps no amount of good experience could counterbalance it. If this is the right view, then a global catastrophe might be something to be welcomed, at least from the impartial or moral point of view.