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July 30, 2021

Arizona wildfire caused by lightningTwo ASU faculty affiliated with the Julie Ann Wrigley Global Futures Laboratory, Michael Barton and Sander van der Leeuw, joined an international panel of 31 natural and social scientists to write a newly published article in Nature Geoscience that investigates abrupt shifts in the Earth's past and how they can be used to predict the future.

The article, Past abrupt changes, tipping points and cascading impacts in the Earth system, was published today an made available with open access by Nature Geoscience.

"We are increasingly concerned about the potential for abrupt changes resulting from human impacts in coming decades," said Barton, director of education and professor at the School of Complex Adaptive Systems. "Equally important, however, are societal dynamics that can make seemingly resilient human systems vulnerable to abrupt economic or political change--or even collapse--from otherwise manageable environmental fluctuations. Study of past socio-environmental tipping points can give us important insights needed to plan for future ones."

The panel of authors used well-documented abrupt changes of the past 30 thousand years of geological history to illustrate how abrupt changes propagate through the physical, ecological and societal components of Earth System. Focusing on two major classes of instabilities in the Earth system caused by ice-ocean interactions and hydroclimate (rainfall) variability, they looked into cascading impacts during the onset of Bølling-Allerød warming about 14,700 years ago and the termination of the African Humid period from 6,000 to 5,000 years ago that led to changes in ecosystems and, presumably, pre-historical societies. They also reviewed useful indicators of upcoming abrupt changes, or early warning signals, and provide a perspective on the contributions of paleoclimate science to the understanding of abrupt changes in the Earth system.

"Nature can be fickle, and rare extreme events like heat and cold waves, thousand-year floods, megadroughts, and wildfires do occur. However, sometimes conditions that are extreme for the past history of a region, like the recent Pacific Northwest heatewave, signal the beginning of a new 'normal'," said Barton. "A trend for hotter summers, colder winters, changing rainfall patterns, more extreme weather or a more active river system are all examples that we can and should be considering."

For the study, the authors determined it was important to decide on the conceptual framework for the analysis, including terminology. They asked questions such as "how abrupt is abrupt?" Considering that there are many definitions of abruptness, they are really context-dependent. The panel decided to use a “faster than the forcing / driving forces” definition according to the relevant IPCC practice. A possibility to decrypt an upcoming abrupt change in temporal or spatial patterns is a novel, powerful method called early warning signals.

Read the full article.