"Regarding your comments on Ian Morris's book, I would take a more pessimistic view. Regarding the Apocalyptic quintet, it is the growth of human population that I consider to be most significant. Of the various civilizations mentioned, let us not forget that in all this time human population was at a fairly stable level of about 500 million. As Roger Martin on BBC hardtalk pointed out the other day, 10,000 people are being born every hour. Another 3 billion souls by 2050. Even if we manage to avoid wars over water and food, I would suggest this planet for most of us then alive is going to be a very uncomfortable place to inhabit. Add to this the Republican ascendancy in the US many of whom cannot even accept, on the evidence, that the Earth is no more than 5000 years old, following from that there is a total blind spot when it comes to the scientific data regarding man made climate change. Little wonder so little was achieved at Cancun. In one of his last TV interviews for the BBC in 1972 the late Alistair Cooke said "I'm a short term optimist, but long term pessimist." That's me, I'm afraid."

David Fuller's view That is an interesting summary and I suspect most people are long-term pessimists. After all, we die and Mother Earth is eventually incinerated. Meanwhile, as one born during WW2 nearly 69 years ago, most of us with an approximately similar lifespan have witnessed more improvement than deterioration, at least in terms of the human condition. We are a clever, albeit highly destructive, species. I have learned to be wary of most long-term trend extrapolations, so I do not take it as a certainty that the human population will continue to increase on its present trajectory until 2050. However if it does, I believe that outcome would require a considerable degree of good fortune, from luck to good scientific planning and innovation. A more immediate problem may be the challenge of feeding the world's poorer populations in the next few years, if turbulent weather conditions continue to play havoc with global crop cycles.