A prestigious group of scientists from around the world is warning that population growth, widespread destruction of natural ecosystems, and climate change may be driving Earth toward an irreversible change in the biosphere, a planet-wide tipping point that could have destructive consequences absent adequate preparation and mitigation.

"It really will be a new world, biologically, at that point," said Anthony Barnosky, professor of integrative biology at the University of California, Berkeley, and lead author of a review paper appearing in the June 7 issue of the journal Nature. "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. This could happen within just a few generations."

The result of such a major shift in the biosphere would be mixed, Barnosky noted, with some plant and animal species disappearing, new mixes of remaining species and major disruptions in terms of which agricultural crops can grow where.

The Nature paper, in which the scientists, including University of New Mexico Distinguished Professor of Biology James H. Brown, compares the biological impact of past incidences of global change with processes currently underway and assess evidence for what the future holds, appears in an issue devoted to the environment in advance of the June 20-22 United Nations Rio+20 Earth Summit in Rio de Janeiro, Brazil.

In the paper, 22 internationally known scientists describe an urgent need for better predictive models based on a detailed understanding of how the biosphere has reacted to rapidly changing conditions, including climate and human population growth, in the distant past.

"There are seven billion people worldwide and a giant global economy," said Brown. "We have the data and if you do the arithmetic, the current situation is unsustainable" said Brown. "We have created a giant bubble of population that must either be deflated gradually or it will burst catastrophically with deprivation and misery everywhere. No one will be immune."

How Close Is a Global Tipping Point?
The authors of the Nature review – biologists, ecologists, complex-systems theoreticians, geologists and paleontologists from the United States, Canada, South America and Europe – argue that although many warning signs are emerging, no one knows how close to a global tipping point Earth is, or whether it is inevitable. The scientists urge focused research to identify early warning signs of a global transition and acceleration of efforts to address the root causes.

"We really do have to be thinking about these global scale tipping points, because even the parts of Earth we are not messing with directly could be prone to some very major changes," Barnosky said. "And the root cause, ultimately, is human population growth and how many resources each one of us uses."

"What we've done as a society," said Brown, "is to create a bubble of population and economy, which is totally dependent on non-renewable resources such as fossil fuels and metals on unsustainable use of renewable resources such as water and fisheries. Flows of these resources to support local and regional economies must come from the global system, where they are simply running out."

Coauthor Elizabeth Hadly from Stanford University thinks that "We may already be past these tipping points in particular regions of the world. 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. We desperately need global leadership for planet Earth."

The authors note that 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 far different from the original in terms of the mix of plant and animal species and their interactions. This is typically accompanied by species extinctions and a loss of biodiversity.

Currently, to support a population of seven billion people, about 43 percent of Earth's 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; at that rate, 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. The last glacial/interglacial transition 11,700 years ago was an example of that," Barnosky said, noting that animal diversity still has not recovered from extinctions during that time. "I think that if we want to avoid the most unpleasant surprises, we want to stay away from that 50 percent mark."

Global Change Biology
The paper emerged from a conference held at UC Berkeley in 2010 to discuss the idea of a global tipping point, how we'd recognize it and how we could avoid it.

Twenty-two of the attendees eventually summarized available evidence of past global state-shifts, the current state of threats to the global environment and what happened after past tipping points.

They concluded that there is an urgent need for global cooperation to reduce world population growth and per-capita resource use, replace fossil fuels with sustainable sources, develop more efficient food production and distribution without taking over more land, and better manage the land and ocean areas not already dominated by humans as reservoirs of biodiversity and ecosystem services.

Media Contacts: UC-Berkeley, Robert Sanders (510) 643-6998; email: rsanders@berkeley.edu; UNM, Steve Carr (505) 277-1821; email: scarr@unm.edu