How much is an elephant worth? Meet the ecologists doing the sums

The idea of being able to put a price on nature is dividing opinion, but the financial value of ecosystem services' is increasingly guiding policy

In 1996, Prof Shahid Naeem was part of a team of researchers who set out to value the Earth. Specifically, they were trying to establish the dollar value of all of the ecosystem services" the planet provides to humans every year. Around $33tn, they concluded, nearly double global GDP at the time.

The team was half ecologists and half economists. The ecologists found the exercise really scary but understood the utility of it. The economists felt nature could be valued but they disagreed about how it could be done," Naeem says.