Nearing the edge
Between this summer’s biblical floods, apocalyptic fires and life-threatening heat domes, people are starting to wonder whether we’ve lurched over some sort of climate tipping point.
Climate scientists and ecologists who study tipping points say what we’re seeing are merely extreme events amplified by global warming. But they’ve been warning about the risk of climate tipping points for years. Now people are listening.
Research published last year in Science suggests the risk of a global tipping point that triggers accelerated climate warming starts to become significant once average worldwide temperatures rise 1.5 degrees C above pre-industrial levels. That’s likely to happen in the 2030s.
In popular usage, tipping points refer to anything that changes suddenly. In science, it usually refers to a straw-that-broke-the-camel’s-back phenomenon, where a small change in input makes a big difference in outcome.
Scientists have documented dozens of regional and local climate tipping points. And long ago, the Earth experienced planet-wide tipping points when the climate whiplashed from an icefree hothouse to a snowball and back again.
What scientists are most worried about now are regional changes that tip into global catastrophes. Timothy Lenton, chair in climate change and Earth system science at the University of Exeter, refers to “tipping elements”—systems of glaciers, forests and coral reefs whose collapse could trigger a form of global warming that feeds on itself. He and colleagues first identified a number of these in a 2008 study, but he said they’re generating much more interest now.
He also led a more recent review of studies highlighting the tipping elements that pose the most immediate threat—the destruction of the West Antarctic and Greenland ice sheets, the thawing of the permafrost and the destruction of the world’s coral reefs.
He said the extreme events making the news this summer might represent an early warning sign he calls flickering—a brief visit to the other side of a tipping point.
The tipping point phenomenon has led to the collapse of local ecologies before, said Simon Willcock, an interdisciplinary researcher at Rothamsted Research in the UK. One good example is the Sahara Desert, which has gone from lush to dry in cycles, the most recent one possibly helped by humans.
In a paper published last month in Nature Sustainability, he and colleagues created complex models of ecosystem collapse, using two examples where tipping points happened in relatively recent history—the Chilika Lagoon in India, where fish populations collapsed, and Easter Island, where deforestation and other environmental stress led to extinction of the local human population.
What he found, he said, was that ecological tipping points can happen much faster than previous models had shown, once they took into account multiple stresses—not just temperature changes, but factors such as overgrazing, deforestation, agricultural runoff and over-fishing.
A climate tipping point could make life a lot harder for our species. We’re not yet over the cliff, but we’re dancing dangerously near the edge.