The effects of global warming are cruelly ironic: the impact of fossil-fuel consumption will be most severe in regions where the least fuel has been consumed. Sub-Saharan Africa is becoming drier: in East Africa droughts of the kind that used to strike every 40 years are arriving every four or five.
On the Indian subcontinent the great centres of population and food production, the valleys of the Ganges, the Brahmaputra and the Indus, are all fed by Himalayan glaciers. These are retreating so fast that the rivers may dry up by 2040. The results will be catastrophic. Bangladesh will be hit twice, as the people of the river deltas are driven off their land by rising sea levels.
Environmental refugees already outnumber those displaced by conflict. Last month Sajeeda Choudhury, the Bangladeshi environment minister, told the BBC that climate change would leave her country with 20m environmental refugees. Rich nations would have to "rethink their immigration policies".
The distinction between political and economic refugees has always been an artificial one: poor regions of the world remain so as a result of the policies of rich. But in this case the West's moral responsibility is incontestable: every time someone in the West turns on a kettle, he or she is helping to flood Bangladesh. Global warming requires an ethical framework that classifies hitherto innocent actions as deadly. There is nowhere else for the displaced people of Bangladesh or sub-Saharan Africa to go. The cities have nothing to offer them: there will be no industrial revolution in these regions. If the West doesn't let them in, they will die, and Westerners, the consumers of fossil fuels, will be responsible. If global warming is not contained, the West will face a choice of a refugee crisis of unimaginable proportions, or direct complicity in crimes against humanity.
The alternative is to reduce carbon consumption by 90% over the next 10 years. This may sound impossible. But there are few economic activities whose impact cannot be cut to this extent, either through technology or reduced consumption, without harming the quality of life. What this requires is radical thinking: the abandonment of gross domestic product as the index of prosperity, confrontation with the most powerful industrial lobbies, regulation that forces producers and consumers to carry their own costs. Is any government brave enough to do this? Is any government brave enough not to?