Climate change has its target — limiting global warming to well below 2°C and pursuing efforts to limit it to 1.5°C. Many people believe that biodiversity needs the same kind of global treatment. Indeed, this week’s World Biodiversity Forum in Davos, Switzerland, will host part of the debate to create formal goals.

They should be careful, Andy Purvis, a research leader at the Natural History Museum in London, told a plenary meeting at the Forum on Tuesday. Climate change and biodiversity are not the same thing. Treating them as such could be dangerous.

“If we are trying to put conserving the biodiversity that we need now, together with conserving biodiversity for its own sake, into a single target, I can only see very bad things coming from that,” he said afterwards during an interview with Future Earth.

Purvis does not for a second believe that the world’s biodiversity is not in trouble. Nor does he think targets a bad thing. His warning referred simply to adopting one overarching target (such as an x-percentage reduction in threatened species by a certain date).

“Biodiversity is definitely declining, and we need big changes in how we manage the planet,” he said. Using data stemming from the International Union for Conservation of Nature, the IPBES Global Assessment, on which Purvis worked, said that around 25 percent of plants and animals other than insects were currently in danger of extinction. (For insects, it was around 10 percent).

Taken together with estimates of global diversity, this amounts to around 1 million species in danger.

The main issue of Purvis’s presentation, however, was for people to recognize how huge biodiversity is – the hint perhaps being the “diversity” part – and not to treat it as one problem.

Purvis reckons that we need to recognize – and keep separate – two reasons for conserving biodiversity. First, ecosystems provide lots of benefits to people; and these mostly come from species that are common in local ecosystems. Second, extinction of the million species would be a global disaster, even if these rare species don’t provide as many tangible benefits. 

The latter are rare and live in restricted areas such as coral reefs, the Andes, the Great Lakes of Africa.

“Losing those would be a shocking tragedy that I firmly doubt future generations will forgive,” he said. But the different categories are poorly correlated and a single target would miss.

Purvis likened biodiversity to human wellbeing – a single concept with vast differences within it. You can’t improve it with one target.

All this will be grist for discussion at the Earth Commission Workshop on Biodiversity Targets which begins on Friday and runs until Monday, sponsored by Future Earth and the Convention on Biological Diversity.  The workshop will bring together biodiversity scientists to consider what science is available to allow for global biodiversity targets for the next decade.