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 create new varieties 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 planet’s surface by a ratio of 95 to 5, Barnosky says. Ten thousand years ago, at the beginning of the Holocene geological epoch, the weight of humans and domesticated animals was just 0.1% of the total.
Since we have become such a dominant force on our planet, 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, as previous efforts have tried to do, some conservationists say we should be realistic and recognise that humans are an integral part of many ecosystems now. In many cases, they argue, 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 beginning to accept and implement this new approach - embracing introduced species, while trying to route out the more harmful invasives that out-compete unique flora or fauna. 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 and 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 you could argue that humans may be acting in time to save endangered species 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. 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 Virgin boss Richard Branson proposed last year.
Paradoxically, just as we approach a tipping point for extinctions, we are beginning to understand how we could 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 means we must develop our 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.