No one should be under any illusion - the very future of our planet is now at risk. Heads of government talk about it, and an increasing number of business leaders acknowledge it. Movies are made about it. Our children are growing up with knowledge of the appalling dangers we all face.

Nightly, television news programmes around the world show us stark images of fights over declining fish stocks, of disappearing forests and eroded landscapes, of waterways poisoned by factory discharges, of polluted air and fast-changing climate...