We're perhaps just decades away from the tipping point that could alter the planet irreversibly, an international group of scientists has warned.
Indeed, in some regions we may have passed that point already, leading to a permanent loss in the number of species and severe effects on human beings.
"The data suggests that there will be a reduction in biodiversity and severe impacts on much of what we depend on to sustain our quality of life, including, for example, fisheries, agriculture, forest products and clean water," warns Anthony Barnosky, professor of integrative biology at the University of California, Berkeley.
"This could happen within just a few generations."
The scientists want to see much better predictive models, and have launched the Berkeley Initiative in Global Change Biology, or BiGCB, a massive undertaking involving more than 100 UC Berkeley scientists from a wide range of disciplines.
"One key goal of the BiGCB is to understand how plants and animals responded to major shifts in the atmosphere, oceans, and climate in the past, so that scientists can improve their forecasts and policy makers can take the steps necessary to either mitigate or adapt to changes that may be inevitable," says Barnosky.
"Better predictive models will lead to better decisions in terms of protecting the natural resources future generations will rely on for quality of life and prosperity."
In a review in Nature, biologists, ecologists, complex-systems theoreticians, geologists and paleontologists from the US, Canada, South America and Europe argue that, although many warning signs are emerging, no one knows for sure how close Earth is to a global tipping point - or even if it really is inevitable.
"We may already be past these tipping points in particular regions of the world," says Elizabeth Hadly from Stanford University.
"I just returned from a trip to the high Himalayas in Nepal, where I witnessed families fighting each other with machetes for wood - wood that they would burn to cook their food in one evening. In places where governments are lacking basic infrastructure, people fend for themselves, and biodiversity suffers."
Studies of small-scale ecosystems show that once 50-90 percent of an area has been altered, the entire ecosystem tips irreversibly into a state very different from the original, with species extinctions and a loss of biodiversity.
Currently, to support a population of seven billion people, about 43 percent of Earth's land surface has been converted to agricultural or urban use, with roads cutting through much of the remainder. The population is expected to rise to nine billion by 2045; and current trends suggest that half Earth's land surface will be disturbed by 2025. To Barnosky, this is disturbingly close to a global tipping point.
"Can it really happen? Looking into the past tells us unequivocally that, yes, it can really happen. It has happened," he says.