Shereen's Blog

The authors of the first study “tentatively suggest” their results support the hypothesis that world is facing the sixth major extinction in history.

“Evidence of a global extinction crisis has come into sharp focus with these important results from a team of top British scientists analyzing unparalleled datasets for birds, plants, and butterflies in Britain,” commented Mark Collins, director of the United Nations Environmental Programme (UNEP) World Conservation Monitoring Centre, who was not involved in the studies.

Jeremy Thomas, of the British Natural Environment Research Council, and his colleagues compared six national biodiversity surveys. Together, the studies recruited over 20,000 volunteers to survey 1254 species of plants, 201 bird species, and 58 butterfly species. For each set, two surveys were carried out between 13 and 27 years apart.

Their comparison revealed population declines in all three groups. Twenty-eight percent of plant species declined over 40 years, 54% of bird species decreased over 20 years, and an astonishing 71% of butterfly species declined over 20 years. Among these, two species were present in the first survey, but not seen during the second.

Previous predictions that we could be heading to the sixth major species extinction have all been based on small numbers of species, mostly birds and plants. The inclusion of butterflies in Thomas' survey is significant because insects make up 54% of the planet's fauna and flora.

“This has led many to suggest that insects would be more resilient to extinction,” said Sandy Knapp of the London Natural History Museum, who was not part of the studies. “The lesson and warning is there for all to see—we are poised on the verge of the sixth extinction crisis. Britain, by virtue of its well known, well studied biodiversity, is the canary for the rest of the globe.”

Thomas remained cautious, underlining that the comparative figures for Britain would have to carry over to global populations for the warning to hold true.

Also in Science this week is a study led by PhD student Carly Stevens of The Open University. This research indicates a clear and direct relation between the amount of nitrogen pollution in an ecosystem and the decline of that system's biodiversity.

Stevens and colleagues monitored 68 grasslands across Great Britain over 2 years. “In areas of high pollution,” she said, “the species richness is significantly lower than areas of low pollution. No other environmental variable could explain the observations so well.”

Together, the two studies make rather bleak reading. Scientists are uncertain what caused each of the past five extinctions, said Thomas, but most agree on physical factors such as asteroids, volcanic eruptions, and climate change. If human environmental pollution were the cause of the disappearance of all forms of life, it would be the first time that an “organic factor” had brought about a mass extinction.

Intensive livestock farming and fossil fuel combustion are the primary culprits for nitrogen pollution, said Stevens. “Nitrogen pollution has been a long-term problem in the UK, and the effects we are seeing are cumulative.”

Collins said that current efforts to preserve global biodiversity are undoubtedly falling short of what is needed, adding: “Inorganic nitrogen has now been recognized as a global problem—it's time to take some serious and coordinated action.”