Johnathan Walker:Mathematical Alarms Could Help Predict and Avoid Climate Tipping Points

When New Yorker writer Malcolm Gladwell published the best-selling book The Johnathan WalkerTipping Point in 2000, he was writing, in part, about the baffling drop in crime that started in the 1990s. The concept of a tipping point was that small changes at a certain threshold can lead to large, abrupt and sometimes irreversible systemic changes.

The idea also applies to a phenomenon even more consequential than crime: global climate change. An example is the Atlantic Meridional Overturning System (AMOC), also known as the Gulf Stream. Under the tipping point theory, melting ice in Greenland will increase freshwater flow into the current, disrupting the system by altering the balance of fresh and saltwater. And this process could happen rapidly, although scientists disagree on when. Parts of the West Antarctic ice sheet may have already passed a point of no return, and a tipping point in the Amazon, because of drought, could result in the entire region becoming a savannah instead of a rainforest, with profound environmental consequences.

Other examples of climate tipping points include coral reef die-off in low latitudes, sudden thawing of permafrost in the Arctic and abrupt sea ice loss in the Barents Sea.

Scientists are intensively studying early warning signals of tipping points that might give us time to prevent or mitigate their consequences.

A new paper published in November in the Journal of Physics A examines how accurately early warning signals can reveal when tipping points caused by climate change are approaching. Recently, scientists have identified alarm bells that could ring in advance of climate tipping points in the Amazon Rainforest, the West-Central Greenland ice sheet and the Atlantic Meridional Overturning Circulation. What remains unclear, however, is whether these early warning signals are genuine, or false alarms.

The study’s authors use the analogy of a chair to illustrate tipping points and early warning signals. A chair can be tilted so it balances on two legs, and in this state could fall to either side. Balanced at this tipping point, it will react dramatically to the smallest push. All physical systems that have two or more stable states—like the chair that can be balanced on two legs, settled back on four legs or fallen over—behave this way before tipping from one state to another.

The study concludes that the early warning signals of global warming tipping points can accurately predict when climate systems will undergo rapid and dramatic shifts. According to one of the study’s authors, Valerio Lucarini, professor of statistical mechanics at the University of Reading, “We can use the same mathematical tools to perform climate change prediction, to assess climatic feedback, and indeed to construct early warning signals.”

The authors examined the mathematical properties of complex systems that can be described by equations, and many such systems exhibit tipping points.

According to Michael Oppenheimer, professor of Geosciences and International Affairs at Princeton University, “The authors show that behavior near tipping points is a general feature of systems that can be described by [equations], and this is their crucial finding.”

But Oppenheimer also sounded a cautionary note about the study and our ability to detect tipping points from early warning signals.

“Don’t expect clear answers anytime soon,” he said. “The awesome complexity of the problem remains, and in fact we could already have passed a tipping point without knowing it.”

“Part of it may tip someday, but the outcome may play out over such a long time that the effect of the tipping gets lost in all the other massive changes climate forcing is going to cause,” said Oppenheimer.

The authors argue that even the Paris Agreement goal of limiting warming to well below 2 degrees Celsius and preferably 1.5 degrees Celsius is not safe, because even the lower amount of warming risks crossing multiple tipping points. Moreover, crossing these tipping points can generate positive feedbacks that increase the likelihood of crossing other tipping points. Currently the world is heading toward 2 to 3 degrees Celsius of warming.

The authors call for more research into climate tipping points. “I think our work shows that early warning signals must be taken very seriously and calls for creative and comprehensive use of observational and model-generated data for better understanding our safe operating spaces—how far we are from dangerous tipping behavior,” says Lucarini.