In around 300 years time, 75% of all mammal species on Earth will have gone extinct. That’s the startling prediction if current rates of extinction continue and the animals already threatened or endangered are wiped out this century, according to Anthony Barnosky, a palaeobiologist at the University of California, Berkeley.
Barnosky studies biodiversity changes and extinction rates that occurred in the deep past, and compares them to trends happening now. Since life first evolved, billions of years ago, flourished, diversified and made our planet truly distinct from any other we’re aware of, there have been five mass extinctions. Each was triggered by a cataclysmic event and resulted in at least 75% of all species going extinct. The last of these occurred 65 million years ago, when a meteorite slammed into Earth, throwing up persistent clouds of debris that darkened the sky for years. The climate change that followed led to the extinction of the dinosaurs and three-quarters of all other animals.
Now, Barnosky calculates, humans are creating a mass extinction on the same scale – the planet’s sixth one – through a combination of habitat encroachment and fragmentation, hunting, climate change, pollution, and the spread of disease and introduced species. Some 30% of all species may be lost over the next four decades, conservationists estimate.
Extinction is actually a natural and common phenomenon – of the roughly 4 billion species estimated to have evolved on Earth, some 99% are gone – however, the extinction rate is usually balanced by the evolution of new species. The current, human-caused extinction is happening so fast that evolution cannot keep pace. Barnosky estimates that the current rate is 1000 times the natural rate, putting it easily on a par with the ‘big 5’ mass extinction events.
The Anthropocene, the Age of Man, will be marked by a rapid decline in biodiversity as animals and plants disappear from the planet – and the fossil record – forever. It won’t just be the individual creatures that vanish, but also their descendants on the evolutionary tree – whole lines of phyla will prematurely cease.
And the Anthropocene will also be notable for its homogeneity – what Barnosky describes as the “McDonaldization of nature”. Many animals and plants have evolved to occupy specific geographical niches, such as islands or mountain lakes. As a result, across the planet it is possible to find endemic species that exist nowhere else on Earth, such as the giant tortoises of the Galapagos, the lemurs of Madagascar or the koalas of Australia. Occasionally, during the history of the Earth, shifting tectonic plates have forced land masses together, enabling the separate biodiversity to mix for the first time. This happened when the North and South American continents smacked into each other, around 3 million years ago, for example. In the invasions that followed, South America got its first large carnivore – the jaguar from North America – which proceeded to eat much of the native fauna, resulting in many extinctions.
Humans have been orchestrating our own tectonic-scale species migrations, either deliberately or accidentally. As a result, some species including rats, goats, rhododendron, wheat and eucalyptus are found around the world. Meanwhile, many others have become rare or vanished. Many of the introduced species are invasive – or ‘weeds’ – which out-compete the natives for food, light and habitat, or simply eat them to extinction.
And we’ve also been spreading pests and diseases from one place or continent to another, often causing local extinctions. Isolated human populations have even been wiped out in this way, when we’ve introduced diseases such as flu, smallpox, HIV or malaria to places where the local people haven’t developed immunity.
Meanwhile, we’ve been artificially boosting the populations of certain select species, such as cows, dogs, rice, maize and chickens – most of which have been bred to new varieties that are radically different from their wild ancestors. The combined weight of humans and the animals we’ve domesticated now outweighs all the wild back-boned creatures on the land surface by 95:5, Barnosky says. Ten thousand years ago, at the beginning of the Holocene geological epoch, that figure was just 0.1%.
So we’re leaving a pretty distinctive mark on the living planet. Nowhere on Earth is truly wild or pristine anymore – everywhere has been touched by humans in some way, from the newly polluted atmosphere that contains different concentrations and isotopes of carbon dioxide, to the sugarcane monocultures that lie where primary rainforest ecosystems once thrived.
Since we have become such a dominant force on our planet, going forward into the Anthropocene we have to decide how best to manage the situation we’re creating. Many are calling for a change in the way that conservation has traditionally been practiced. Instead of battling to return ecosystems to a pre-human state, they say we should be realistic and recognise that humans are an integral part of many ecosystems now. This new-guard of conservationists argue that in many cases, we should accept ecosystems that incorporate non-native species, value them and try to conserve them as ‘novel ecosystems’ that are worth protecting.
From Hawaii to the Galapagos, conservationists are switching tack and starting to embrace the introduced species of Anthropocene ecosystems, while focusing their efforts on rooting out the more harmful invasives that out-compete unique flora or fauna. Thus, in the Galapagos, plagues of blackberry bushes originally from the Himalayas are simply being controlled, whereas rats and goats that eat the food of rare tortoises are being eliminated.
In other places, such as the vast monocultures we create through agriculture, efforts are already being made to restore native ecosystems, or in some cases plant non-native trees, grasses or introduce animals to restore the functions that the pre-human ecosystem once provided, such as reducing soil erosion, pollinating flowers or controlling wildfires.
There have never been so many areas of conservation – national parks and protected zones – so for some endangered species, humans may be acting in time to save them from extinction. But many of these areas are protected in name only – the parts of the world with the greatest biodiversity are often in the poorest and most troubled regions, such as the Congo and Borneo.
It is fairly certain that the Anthropocene will be a time of much poorer biodiversity in which once-common species will be extinct or exist only in human-made environments like zoos or private breeding colonies far from their natural habitat, such as the lemur sanctuary in the Caribbean that Richard Branson is proposing.
Paradoxically, just as we approach a tipping point for extinctions, we are beginning to understand how to bring extinct animals back from the dead. Scientists are hopeful of cloning mammoths and even restoring our own extinct cousin, the neanderthal. Sadly, expensive techniques like this, even if successful for individual animals, could not be applied practically to restore the intricate diversity of life that existed before humans took over the planet. Instead, in our human world, we must decide what type of ecosystems we would collectively like, and set about creating and protecting them. In the Anthropocene, we are no longer just another part of the natural world, we are the planet’s gardeners and that requires nurturing skills.
You can hear my conversations with Barnosky and others, discussing our impacts on the planet’s biodiversity and geology, in a four-part series called The Age We Made, broadcast weekly on BBC World Service from Mondays at 19.32 GMT.