So, what are the possibilities?
He quotes from a scientific paper by Nasa's Professor James Hansen, which says that the last time the world warmed by 2-3 degrees C in such a short time, the world's major ice sheets collapsed very quickly - and sea levels rose by 25 metres. "If that happens again," he says, "it would inundate the areas where 60 per cent of human beings live."
Yes, but which 60%?
If Hurricane Katrina in New Orleans, or what happened in Tewkesbury taught us anything, it is that poor people are less likely to have house insurance, the ability to migrate or resources to rebuild their lives. It's clear that it won't be scientific debate that sets the level of carbon emission reductions, it will be the result of struggle between the haves and the have-nots. Quite simply, the rich and powerful - for now - can tolerate higher levels of climate change because they can pay to escape the consequences.
Katrina also showed something else, didn't it?
A partial ethnic cleansing of New Orleans will be a fait accompli without massive local and federal efforts to provide affordable housing for tens of thousands of poor renters now dispersed across the country in refugee shelters. Already there is intense debate about transforming some of poorest, low-lying neighbourhoods, such the Lower Ninth Ward (flooded again by Hurricane Rita), into water retention ponds to protect wealthier parts. As the Wall Street Journal has rightly emphasised, “That would mean preventing some of New Orleans’s poorest residents from ever returning to their neighbourhoods”
They call it creative destruction.