Earth may be approaching 'tipping point,' Stanford scientist says

The planet may be nearing a critical threshold, beyond which environmental changes will be rapid and unpredictable, according to a study co-authored by Stanford Professor Elizabeth Hadly.

Illustration by Cheng 'Lily' Li Illustration of globe being pushed over cliff

The consensus statement by 22 respected scientists uses past examples to suggest that Earth's current systems will experience a major disruption - perhaps within a few generations. 'The environment will enter a new state,' said Stanford Professor Elizabeth Hadly. 'And we don't know exactly what that state will look like.'

Yellowstone is the nation's oldest national park – it has been protected since 1872. So when Stanford biology Professor Elizabeth Hadly saw several years ago that its wetland cover and amphibian populations were both declining, she was a little surprised.

"Practically its entire watershed is protected," she said. "These changes weren't caused by something from inside the park."

Yellowstone was providing evidence to support a growing suspicion held by Hadly and a large number of other prominent environmental scientists.

Most current predictions of environmental change are based on extrapolations from current trends. But what if that isn't an accurate picture of the future? What if we are approaching a critical threshold – one that, once crossed, would lead to accelerated, widespread and largely unpredictable environmental degradations?

This is the frightening conclusion of a paper co-authored by Hadly that appears in the new issue of Nature – an issue devoted to the environment, in anticipation of the United Nations' June 20-22 Conference on Sustainable Development. The consensus statement by 22 respected scientists uses past examples to suggest that Earth's current systems will experience a major disruption – perhaps within a few generations.

"The environment will enter a new state," said Hadly. "And we don't know exactly what that state will look like."

Reaching the tipping point

It's already established that global biological systems are capable of very rapid, wholesale shifts. Of the five major extinction events in Earth's history, at least four of them were accompanied by this kind of critical transition. Global conditions that had remained relatively stable for millions of years changed dramatically over a period lasting less than 5 percent of that time.

There's reason to believe that "pronounced change" in "assemblages of species," as the paper puts it – such as extinction events – are a reliable marker of these shifts. And we happen to be in the middle of an ongoing human-driven mass extinction.

The litany of ways in which humans have altered the Earth's environment is well known. But why do these scientists now believe that we are moving toward a major, irreversible shift?

"There's the idea that, once you have more than 50 percent of wholesale disturbance in a given ecological system, major disturbance in the rest of the system will inevitably follow," said Hadly, who is also a senior fellow at the Stanford Woods Institute for the Environment.

L.A. CiceroElizabeth Hadly portrait

Professor Elizabeth Hadly

About 43 percent of Earth's land has already been converted to agricultural or urban use and, if current trends continue, is expected to reach the 50 percent mark by 2025. By 2060, using current trends, the number will be 70 percent.

By comparison, the last critical shift Earth underwent was the end of the last Ice Age. That famously dramatic example of climate change only involved ice melting from 30 percent of Earth's surface, and it resulted in a major transition in global climatic conditions and the distribution of life on the planet.

No escape

What Hadly saw in Yellowstone suggests these global shifts may already be affecting isolated, local environments.

"As an ecologist, I was trained to measure changes on a local or a regional level – looking at changes in a 1-by-1-meter plot," said Hadly. "Now, there's a heck of a lot of change in that 1-meter plot that has nothing to do with local processes."

The global drivers that are working their way into every corner of the planet all have humans behind the wheel. Human population growth and increased resource consumption mean that anywhere from 20 to 40 percent of the planet's energy produced by living things now goes to support human society.

The ecosystems that do survive are becoming more homogeneous and simpler – a combination of human-introduced species and habitat degradation and fragmentation.

"We're fairly naïve in managing for new combinations of species that will exist," Hadly said, "in part because we usually anticipate ecosystem change on a species-by-species basis."

The human connection

Although the exact nature of Earth's next state is unpredictable, the researchers expect it to resemble an accelerated version of these already-in-motion processes.

These shifts are potentially disastrous for humanity as well.

"Citizens of wealthy countries like the U.S. are less aware of catastrophic shifts in ecosystem services because we have the ability to cobble together short-term fixes that mask the global trend," said Hadly. "But other countries aren't so buffered." In a world marked by water shortages and climate change, "we simply aren't yet equipped with a flexible intergovernmental structure necessary to manage for this future."

The United States may be buffered, but it can help with a crucial environmental task: monitoring ecosystems for evidence of this shift. America is large and geographically diverse enough that, Hadly says, "we could be some of the first to observe these changes, and if we are proactive, we can bear witness to the rest of the world."

Which will be crucial for predicting when the shift is coming – or if it's already here.

Elizabeth Hadly, Biology: (650) 725-2655,

Max McClure, Stanford News Service: (650) 725-6737,