To protect the health of humans, save other species. That's the message from Eric Chivian and Aaron Bernstein from Harvard Medical School in Boston, who say that human health depends crucially on biodiversity.

Demand for plant products has never been greater, more people, rising affluence, and expanding biofuels programs are rapidly pushing up the prices of grain and edible oil. Boosting supply isn't easy: All the best farm land is already in use. There's an acute need for another jump in global agricultural productivity-a second Green Revolution. Can it happen? Will it happen? (Editorial)

There's little doubt that free-market capitalism helped to get us into the mess we're in. As Nicholas Stern, former chief economist at the World Bank, puts it: climate change is "the greatest market failure the world has ever seen". The question now is whether capitalism is able to make amends. Can it provide a mechanism that rewards people for reducing their carbon emissions instead of increasing them? Or will it simply give big polluters a way of dodging their responsibilities?