Could human activity push Earth’s biological systems to a planet-wide tipping point, causing changes as radical as the Ice Age’s end — but with less pleasant results, and with billions of people along for a bumpy ride?
It’s by no means a settled scientific proposition, but many researchers say it’s worth considering — and not just as an apocalyptic warning or far-fetched speculation, but as a legitimate question raised by emerging science.
“There are some biological realities we can’t ignore,” said paleoecologist Anthony Barnosky of the University of California, Berkeley. “What I’d like to avoid is getting caught by surprise.”
In “Approaching a state shift in Earth’s biosphere,” published June 6 in Nature, Barnosky and 21 co-authors cite 100 papers in summarizing what’s known about environmental tipping points.
While the concept was popularized by Malcolm Gladwell’s accounts of sudden, widespread changes in society, the underlying mathematics — which won physicist Kenneth Wilson a Nobel Prize in 1982 — have far-reaching implications.
In the last few decades, scientists have found tipping behaviors in various natural environments, from locale-scale ponds and coral reefs to regional systems like the Sahara desert, which until 5,500 years ago was a fertile grassland, and perhaps even the Amazon basin.
Deforestation in the Amazon jungle, which some scientists say could become a savannah. Image: NASA
Common to these examples is a type of transformation not described in traditional ideas of nature as existing in a static balance, with change occurring gradually. Instead, the systems seem to be dynamic, ebbing and flowing within a range of biological parameters.
Stress those parameters — with fast-rising temperatures, say, or a burst of nutrients — and systems are capable of sudden, feedback loop-fueled reconfiguration.
According to some researchers, that’s what happened when life’s diversity exploded in an eyeblink 540 million years ago, or much more recently when a glacier-chilled Earth became in a couple thousand years the temperate garden that cradled human civilization.
But while the Cambrian explosion and Holocene warming were sparked by natural, planet-wide changes to ocean chemistry and solar intensity, say Barnosky and colleagues, there’s a new force to consider: 7 billion people who exert a combined influence usually associated with planetary processes.
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