There is a general agreement among scientists that extinction rates have reached levels unparalleled since the dinosaurs died out approximately 65 million years ago. However, some have challenged the theory, believing earlier estimates rested on assumptions that overestimated the crisis.
A new study, published in the journal Science Advances, is likely to put these doubts to rest – even with extremely conservative estimates, our planet is already entering its sixth mass extinction event. Species are disappearing up to about 100 times faster than the rate between extinctions, known as the “background rate”.
“If it is allowed to continue, life would take many millions of years to recover, and our species itself would likely disappear early on,” said study lead author Gerardo Ceballos of the Universidad Autónoma de México.
Owing to the need for assumptions on sparse data, estimating modern extinction rates is an extremely tricky business. With this in mind, Ceballos and his international team of scientists wanted to put the floor on these numbers and establish the most conservative estimates possible. This means that whatever the actual rates are, they could not be any lower.
Taking their efforts even further, the researchers also used a new, updated, background rate, which puts the annual loss of species at 2 per every million – effectively doubling the assessments provided in studies conducted in the past.
“We emphasize that our calculation very likely underestimates the severity of the extinction crisis, because our aim was to place a realistic lower bound on humanity’s impact on biodiversity,” explained the authors.
The result? Even with these – one might say, excessive – cautionary measures, current extinction rates are far, far greater than the going-on-all-the-time extinction that is largely independent of human involvement.
The spectre of extinction now hangs over 41% of all amphibian species and 26% of all mammals, according to the International Union for Conservation of Nature, which maintains an authoritative list of extinct and threatened species that stretches back all the way to the year 1500.
“These are examples of species all over the world that are essentially the walking dead,” said a study co-author Paul Ehrlich from the Stanford Woods Institute for the Environment.
Thanks to extensive logging, ambient pollution, the clearing of land for farming, climate change and many other negative effects of the spreading human civilization, much of the current benefits we derive from robust levels of biodiversity might be lost in just three generations.
But it’s not just the technically-obvious disadvantages that we should be worried about:
“If we regard the Earth as nothing more than a source of resources and a sink for our pollution, if we value other species only in terms of what they can provide to us, then we we will continue to unpick the fabric of life. Remove further rivets from spaceship earth. This not only increases the risk that it will cease to function in the ways that we and future generations will depend on, but can only reduce the complexity and beauty of our home in the cosmos,“ writes James Dyke, a Lecturer in Complex Systems Simulation at the University of Southampton.
To mitigate the disruptive effects of the rising human population and the ever-increasing levels of consumption, rapid and greatly intensified global efforts will be required.
In the meantime, the authors of the study hope it will command the attention of various national and international representative bodies, inform conservation efforts, the maintenance of ecosystem services and public policy.