A barometer measures atmospheric pressure. Now a coalition of biologists is calling for a similar scientific tool to measure extinction pressure on Earth's biodiversity—a so-called "barometer of life".

After all, scientists have conclusively identified only a fraction of the species that exist on Earth; the roughly 1.9 million species catalogued to date may represent only 20 percent of the total biodiversity on the planet. "Species disappear before we know they existed," wrote biologists Simon Stuart, chair of the Species Survival Commission at the International Union for Conservation of Nature (IUCN), Edward O. Wilson of Harvard University, and others in the April 9 issue of Science, calling for an international effort to fund the creation of such a bio-barometer. Adds Stuart: "The point of conservation is to turn that negative trend into a positive trend."

The biologists propose to do that by spending $60 million to pull together all the known information to assess roughly 160,000 individual species from four groups: chordates (mammals and other vertebrates); invertebrates (insects and worms); plants; and fungi. The species would be assessed to identify which are suffering as a result of various extinction pressures: agricultural expansion and/or intensification; habitat changes; and climate change, among others. Such an assessment would give a better picture of the overall threat to biodiversity than do current efforts, according to the biologists. "There's an awful lot of information out there that we're not using because it's sitting in obscure places like museum jars," Stuart says.

Of course, 160,000 is only roughly 8 percent of known species—and the survey will not attempt to expand the rolls of living things, like the Encyclopedia of Life (an effort to catalogue all the species on the planet). "We're not going to be able to monitor the conservation status of nematodes anytime soon," Stuart admits. But "if the barometer shows a very major decline—as [the IUCN Red List of Threatened Species suggests already]—in mammals due to overhunting in Asia then that informs us what needs to be done."

As the aforementioned Encyclopedia and Red List suggest, the barometer would be only one of many such efforts, particularly given that this is the International Year of Biodiversity, according to the United Nations. But many of those efforts, including the IUCN's, cover even fewer species and betray a distinct bias toward charismatic megafauna like polar bears or bald eagles.

Other conservation groups take a different approach: The Nature Conservancy will release its Atlas of Global Conservation on April 22, which attempts to capture in maps the pressures faced by global habitats as well as the relative density of various species, such as amphibians. "By taking a habitat view, you're able to encompass all those species," says Conservancy senior scientist Jennifer Molnar. "It's a new view of the planet."

The new maps, which rely on collating everything from satellite data to field expeditions to fish species counts in specific locales, reveal that most areas of the world have already warmed as a result of climate change; almost all coastal ecosystems are now impacted by excess flows of nitrogen and other fertilizers, along with a decrease in sediment; and many regions of the world (if not all, because the rest lack sufficient data) now enjoy at least five invasive mammal species and three invading freshwater plants or animal species. "It's the first time to see how bad the problems are at a global scale," Molnar says. "We're not just damaging the environment, we're hurting ourselves…. The maps show that these resources are threatened beyond what we may realize."

The maps might show that current conservation efforts have failed, given that global species-saving efforts have grown as have the extent of protected habitats, although IUCN's Stuart rejects that claim. "Things would be going very much worse were it not for conservation measures," he says. "What we don't know at this stage is how much conservation has achieved." Given that Earth may be losing as many as 140,000 species a year—most of those nematodes and other uncharismatic microfauna—the question of how well conservation has worked to preserve biodiversity may soon be moot.