TIPPING POINT: Climate change, habitat loss, population growth and other human impacts may be pushing the planet toward a critical transition to another ecological state. Image: Flickr/NasaEarthObservatory
Human activities are pushing Earth toward a "tipping point" that could cause sudden, irreversible changes in relatively stable conditions that have allowed civilization to flourish, a new study warns.
There are signs that a toxic brew of climate change, habitat loss and population growth is dramatically reshaping life on Earth, an international team of researchers reported yesterday in the journal Nature.
Those pressures are greater than the natural forces that caused the end of the last ice age roughly 11,700 years ago, a time when half the planet's large mammal species went extinct and humans migrated out of Africa.
"We are doing enough to cause one of these tipping points," said lead author Anthony Barnosky, a paleobiologist at the University of California, Berkeley. "The question now is, how close are we? Is it inevitable? What are the changes that we see coming down the road that we should be aware of in order to make the best of it, essentially."
The answer provided by Barnosky and more than 20 other experts in paleontology, ecology, geology, population biology and complex systems isn't comforting.
The scientists say it's likely -- though not certain -- that Earth is close to another wholesale transformation, but when that will happen and whether it will be irreversible isn't clear.
"We know that at the landscape scale, if you disturb between 50 to 90 percent of patches, you see major changes in ones that you haven't disturbed directly," Barnosky said. "We know that we are at a point on the planet where you have more than 43 percent of the land surface wholesale transformed for human needs. If we transform more and more, we'll be at a point where even places we haven't transformed with our sledgehammers will go through major changes."
The researchers say there is a pressing need for better models and observations to help anticipate future changes and determine how close the planet is to a global tipping point.
The difficulty lies in developing methods to pinpoint the thresholds beyond which systems can flip from relative stability or slow, linear change to rapid transformation.
Scientists hope to reduce 'biological surprises'
"We need to be able to anticipate what are the worst-case scenarios and develop work-arounds in time to actually work around them," Barnosky said. "What we don't want are huge biological surprises that affect how we grow our food or where we get our water."
The idea isn't new. In recent years, scientists who study the climate have argued that humans have changed it enough to push Earth into a new geologic epoch, the Anthropocene. Biologists have warned that accelerating rates of species loss suggest the planet is entering the sixth great extinction in its history, on par with the event that wiped out the dinosaurs.
In 2009, another international team of scientists publishing a study in Nature attempted to lay out a series of seven "planetary boundaries" to preserve conditions in which humans can thrive -- and argued that the world has blown by three of those boundaries already.
"They're all pieces of the same puzzle," Barnosky said. "What's different about what we've come up with here is that we've looked at the past. We talk about the Anthropocene and all of these changes, but there hasn't really been a context to put it in."
The new study uses seven major, undisputed planetary shifts as its benchmarks: the transition 11,700 years ago from the last ice age to the current "interglacial" climate; the five mass extinctions that occurred 65 million, 200 million, 251 million, 359 million and 443 million years ago; and the Cambrian explosion 540 million years ago, when the number and type of species increased rapidly.