As long as it is broad as it is complex, the IUCN Red Listmakes for a sobering read. Over hundreds of pages, it catalogues the perceived and real threats to wildlife all over the world.

To flick through the digital tome is not only to learn the names of countless unfamiliar species, but to be made most acutely aware of the impact of human behavior on their survival. Noted justifications for species' assessed vulnerabilities include trapping for trade, deforestation, habitat loss, environmental degradation and hunting.

With more than 82,000 species already featured and a stated aim to have evaluated 160,000 by the year 2020, the document serves as a barometer for the wellbeing of our planet's flora and fauna, or "an alarm bell," as Craig Hilton-Taylor, who heads the Red List Unit, puts it.

"It is a conscience for the world," he adds, "It says 'hey, there's something happening in this species, you need to do something about it.'"

Categories and criteria

And that is exactly what he and a network of some 10,000 scientists, many of whom have spent decades in the field working on their specialist species, are constantly trying to do. Since its inception in the early '60s, the Red List has undergone significant change and refinement. The most notable was in the '90s, when its increasing global use highlighted the need for clear assessment criteria for endangered status as opposed to the then predominant principle of categorization by subjective opinion.

"The big decision was what were we trying to measure," Hilton-Taylor told DW, adding that the easiest thing was to use available information on threats and population status to look at the likelihood of a species going extinct. "So we came up with a series of criteria with quantitative thresholds which have to be met in order to list the species in different risk categories."

By applying the criteria, which include things like the size and fragmentation of populations, range and rate of decline, the IUCN determines whether a species should be classified as near threatened, vulnerable, endangered, critically endangered, extinct in the wild or indeed entirely.

Hilton-Taylor likens the role of the list to that of an emergency room triage nurse who assesses whether a patient needs to see a doctor right away. "We are trying to see how bad things are and present that evidence with ideas about what can be done."

A flawed concept?

But Brendan Godley,Director of Exeter University's Centre for Ecology and Conservation says the information put forward in the list doesn't always portray things as they really are.

"Although it is objective in its criteria, the use of that criteria can be applied subjectively to give the answer some people want," he said, adding that if a population of a species were declining fast in some countries but increasing in the majority of its range, the possible downlisting from Endangered to Threatened could affect funding opportunities.

Citing sea turtles as a prime example of a species that has been red listed in a way that paints a more dramatic picture than is warranted, he says if there are 20 populations of sea turtles, 19 of which are thriving, and one of which is in serious decline, it does not mean the entire species is at risk. He therefore stresses the need for honesty about where the problems are so that conservation efforts can be channeled in the right direction, while simultaneously keeping a watch on the species overall.

"We can't always be invoking the precautionary principle to the point that we come out with preposterous answers, because then you give the naysayers bullets to undermine the conservation narrative," said Godley.

An open book

Hilton-Taylor, however, insists that the Red List process is transparent and open, and that if anyone has evidence to suggest the official status of a species is inaccurate, they are invited to submit that data and meet with the original assessors to compare notes, and if appropriate, come to a new joint conclusion.

And that is one of the great strengths of this conservation magnum opus: it is under constant review and can be updated to reflect our changing world with relative ease. Of the more than 82,000 species that already feature in the listing, many have been assessed up to six times. This year alone, Red List partners BirdLife Internationalare evaluating the status of the world's entire bird population. In addition to that, up to 2,000 other species of flora and fauna will be newly documented.

"We recognise that the list can sometimes overestimate or underestimate extinction risks, but because we are doing repeat assessments, that allows for things to be brought into balance again," Hilton-Taylor said.

Strength in numbers

It is, as he is at pains to point out, "a long-term" project. Indefinite perhaps, and though it might, like most things in life, have certain imperfections, it is an invaluable tool in the fight to ensure our world remains a place in which as much of our biodiversity not only has the chance to survive, but to thrive.

To date, the list has brought numerous species including the red-cockaded woodpecker, the island fox and the Grand Cayman blue iguana back from the teetering brink of extinction, and has spawned conservation interest in taxa that might otherwise have slipped almost unknown off the face of the earth.

And that is encouraging for the man who heads the Red List Unit. "It shows what an incredible challenge we have out there, but there are amazing success stories where good concerted conservation efforts with local communities and authorities, governments and civil societies all pulling their weight together can turn things around very quickly."