Last century was the warmest for 1800 years. Earth's average surface temperature apparently is now higher than for the previous 100 000 years. Combinations of long cycle variations in orbital and planetary motion cause changes in the world's climate, as do shorter term irregular variations in solar activity and vulcanism. Extraordinarily, the human enterprise is now so large that we are imposing extra “forcing” on the climate system, via emission of greenhouse gases.1 2

The anticipated change in climate (average global warming of around 2-3°C by 2100) would be extremely rapid in geological terms1 2—and much faster than the environmentally disruptive warming that began around 15 000 years ago, after the last ice age. If we cannot reduce our escalating emission of greenhouse gases radically in the next few decades, climate change will continue for centuries and the oceans will rise for millennia.1 Inevitably this would further heighten the risks to …