How can the human race survive the next hundred years? I don't know the answer. That is why I asked the question, to get people to think about it, and to be aware of the dangers we now face.

Before the 1940s, the main threat to our survival came from collisions with asteroids. Such collisions have caused mass extinctions in the past, but the last one was 70m years ago, so the likelihood that we will need the services of Bruce Willis in the next hundred years is very small.

A much more immediate danger, is nuclear war. America and Russia, each have more than enough warheads to kill everyone on Earth, several times over, and the same may now be true of China. The world came perilously close to nuclear annihilation on more than one occasion in the last 50 years. With the ending of the cold war, the threat has become less acute, but it has not gone away. There are still enough nuclear weapons stockpiled to kill us all, and their use might be triggered by an accident that convinced a country that it was under attack. There is now a new danger from small and potentially unstable countries acquiring nuclear weapons. Such minor nuclear powers might cause millions of deaths, but they would not threaten the survival of the entire human race, unless they sparked a conflict between the major powers.

These dangers of asteroid collision and nuclear war, have now been joined by a host of other threats to our survival. Climate change is happening at an ever increasing rate. While we are hoping to stabilise it, and maybe even reverse it, by reducing our CO2 emissions, the danger is that the climate change may pass a tipping point at which the temperature rise becomes self sustaining.

The melting of the Arctic and Antarctic ice reduces the amount of solar energy that is reflected back into space and so increases the temperature further. The rise in sea temperature may trigger the release of large quantities of CO2, trapped at the bottom of the ocean, which will further increase the greenhouse effect. Let's hope we don't end up like our sister planet Venus with a temperature of 250C and raining sulphuric acid. There are other dangers, such as the accidental or intentional release of a genetically engineered virus. Each time we increase our technological powers, we add new possible ways in which things could go disastrously wrong. The human race faces an increasingly dangerous future. There's a sick joke that the reason we haven't been visited by aliens is that when a civilisation reaches our stage of development, it becomes unstable and destroys itself. In fact, I think there are other reasons why we haven't seen any aliens, but the story shows how perilous the situation is. The long-term survival of the human race will be safe only if we spread out into space, and then to other stars. This won't happen for at least 100 years so we have to be very careful. Perhaps, we must hope that genetic engineering will make us wise and less aggressive.