Extrapolation of witnessed species decline shows mean biodiversity loss predictions under continued climate change within the 21^st century may be on the conservative side.

The present century is regarded by ecologists as the first stage in the Holocene Extinction. Within this century a culmination of increasing anthropogenic environmental stressors may even lead to the collapse of entire ecosystems, like the Arctic or the Amazon. As many species are inter-dependent the associated biodiversity declines trigger positive feedbacks to further decline – and over a period of 300 years perhaps as much as 75 percent of all species could die out, a true mass extinction in less than the blink of a geologist’s eye.

One of the major drivers behind the current biodiversity crisis is climate change. So far though it has been difficult to assess both the amount and speed of species decline the current warming will provoke*.

[*) From the fossil record we know a couple of degrees of warming can indeed lead to massive extinction – but that is on ‘a green planet,’ one without industrial overfishing, CFKs, 24h intercontinental transport and monoculture plantations in place of rainforests – one that used to have no more than one sustainability crisis to handle at once.

The other big difference between paleoclimatology and the current climate change is the timescale. Ancient climatic changes usually happened over anything between millennia and millions of years. Today we change the world in a human’s lifetime.

The time difference is to our own advantage [après nous le deluge] too. We won’t live to see many of the changes we set in place and we won’t suffer the damage ourselves. That is why the estimates and predictions for climate change effects usually focus on comprehensible years like 2050 and 2100 – numbers we can to some extent relate to (even though this disregards a big chunk of the scientific urgency for ecology and the planet).]

Predicted and observed species decline

According to a new study by two University of Exeter ecologists, who have published in PNAS yesterday, the mean prediction for climate-induced extinction risk, over different studies and geographical regions, lies at 10 percent for the year 2100, meaning at the end of the century 1 in 10 species is at risk of extinction.

And this figure they say could be on the conservative side. Extrapolating witnessed biodiversity loss in regions that are already affected by significant warming, like the Bering Sea or high-latitude mountain areas, confirms the detrimental effect of climate change on biodiversity that theory describes and suggests this threat could be 40 percent bigger than the predictions have suggested. According to the Exeter researchers’ findings by the year 2100 – we have to repeat excluding other environmental threats – climate change would pose a general extinction risk of 14 percent.

Risk of underestimation remains

Of course for such studies scientists use climate change scenarios – IPCC’s medium variant. We may also have to take into account that here too empirical evidence shows reality is worse than predictions. And of course a larger warming for 2100 can only increase all secondary climate effects, indeed, like biodiversity loss.

© Rolf Schuttenhelm | www.bitsofscience.org