Skip to content

25th Anniversary series: Biodiversity under threat – is the sixth mass extinction already under way?

July 22, 2015

We’ve known for many years that human activity can have a damaging effect on many ecosystems, threatening biodiversity. Now a study claims that the scale of this effect is so much greater than we thought, to the extent of being a “mass extinction”, the sixth in the history of the planet.

Previous mass extinctions were the result of natural processes, like the meteor or asteroid thought to have wiped out the dinosaurs. About 250 million years ago, life on the earth nearly ceased to exist: 90 percent of marine life and 70 percent of terrestrial life died out. This has been attributed to a super-volcano explosion in Siberia that continued off and on for about a million years, with basalt lava and poisonous gases seeping up through cracks in Siberia’s mantle.

Humans have been driving species extinct in all our 200,000 years on the planet – maybe 1,000 species already. Even since 1500 we have killed off at least 300 species and according to the International Union for the Conservation of Nature, another 20,000 species are now threatened.

The term “sixth mass extinction” has been around for some time, with Elizabeth Kolbert winning the Pullitzer prize for best non-fiction, with a book of that title.

Now in a careful study, US scientists compared current extinction rates with a “background rate” of 2 mammal extinctions per 10,000 species per 100 years – a conservative estimate twice as high as previous estimates. Based on this measure, just nine vertebrate species should have disappeared from the earth since 1900. But some 477 extinctions were identified, which should have taken as many as 10,000 years to occur. The average rate of vertebrate species loss over the last century is up to 100 times higher than the background rate. This makes the species extinction rate the highest it has been in 65 million years.

This, the scientists say, indicates the “sixth mass extinction” is already under way. “There are examples of species all over the world that are essentially the walking dead”. And we will be among then – perhaps within as little as three human lifetimes.

Biodiversity blog

Crucial ecosystem services, such as crop pollination and water purification, will suffer if high rates of extinction persist. As our ecosystems unravel, the Centre for Biological Diversity has noted that we could face a “snowball” effect whereby individual species extinction ultimately fuels more losses.

The scientists are in no doubt that human action is the main driver of this dramatic rate of species loss. A high per-capita use of fossil fuels, habitat destruction, land degradation, over-population and the over-exploitation of ecosystems for economic gain are quoted as major contributing factors.

It took millions of years for the planet to re-diversify after the previously recorded mass extinctions, so these consequences would be effectively permanent on human time scales.

So can a disastrous decay of biodiversity and the loss of ecosystem services be averted? The scientists aren’t very confident – rapid, greatly intensified conservation efforts may potentially slow the process, but “the window of opportunity is rapidly closing”.

There are many excellent guides to major trends that will affect us all over the next decades. For guidance, see . What we have tried to do in this blog sequence is to highlight a specific emerging change from the many, and to explore some of the potential impacts.  We welcome thoughts on other drivers of change or more impacts of the ones we have highlighted.

Written by SAMI Principal, Huw Williams.

If you enjoyed this blog, sign up for our monthly newsletter at and/or browse our website at

No comments yet

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.

%d bloggers like this: