In this chapter and the next, so many risks are listed that it could seem surprising that the human race has survived so long. Now, it might indeed be surprising (although of course if the race hadn’t survived, then we’d not be here to observe and discuss the matter). On the other hand, it may well be that the risk of extinction has so far been fairly low. What then needs to be feared is a sudden increase in various dangers.
The chapter expands points made in the Introduction about well-known risks. The continued career of the human race is endangered by chemical, biological and nuclear war, by destruction of the ozone layer and greenhouse-effect overheating (conceivably of a runaway kind in which warming releases more and more methane, a powerful greenhouse gas), by desertification and pollution of land and sea, by loss of biodiversity and by diseases. Overpopulation, a main cause of the deterioration of the environment, may also lead to global warfare.
Some lesser-known risks are discussed in Chapter 2. And for the moment nothing is said about the dangers presented—if anyone listens to philosophers—by philosophical doctrines which suggest that the extinction of humankind would be no real disaster. Those doctrines are discussed in Chapter 4.