![]() ![]() One good example is the Sahara Desert, which has gone from lush to dry in cycles, the most recent one possibly helped by humans. 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. “A complex system can sometimes start to sample a different regime or state before it takes a more permanent shift into that state,” he said. 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. 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 and colleagues first identified a number of these in a 2008 study, but he said they’re generating much more interest now. 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. What scientists are most worried about now are regional changes that tip into global catastrophes. After the advent of complex life, some of these led to mass death and extinction.Īnd one more reason to be concerned today: The rate of change we’re imposing on the planet is “geologically unusual,” as planetary scientist Andy Knoll told me then. And sudden shifts in climactic feedback loops did roil the planet. Even so, for most of that history, there was no complex life - only bacteria. Looking at some of that long-term history for an Earth Day column a few years ago, I talked to scientists who marveled that Earth has been habitable for almost its entire existence - nearly 4 billion years - thanks to stabilizing feedback loops. And long ago, the Earth experienced planet-wide tipping points when the climate whiplashed from an ice-free hothouse to a snowball and back again. Scientists have documented dozens of regional and local climate tipping points. Physicists refer to this as a positive feedback loop, but from our standpoint it won’t be beneficial. When climate scientists talk about tipping points, they’re looking at a shift in feedback loops - the disruption of stabilising feedback loops and the start of new ones that amplify change. 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. In popular usage, tipping points refer to anything that changes suddenly. 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 1.5C above pre-industrial levels. But they’ve been warning about the risk of climate tipping points for years. Climate scientists and ecologists who study tipping points say what we’re seeing are merely extreme events amplified by global warming. 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.
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