Climate ‘tipping points’ prove unpredictable

UC DAVIS (US)—Sudden shifts in Earth’s natural systems may be harder to foresee than previously thought, worrying scientists trying to identify dramatic global climate changes before they occur.

“Many scientists are looking for the warning signs that herald sudden changes in natural systems, in hopes of forestalling those changes, or improving our preparations for them,” says Alan Hastings, a professor in the Department of Environmental Science and Policy at University of California, Davis.

“Unfortunately, regime shifts with potentially large consequences can happen without warning—systems can ‘tip’ precipitously.

“This means that some effects of global climate change on ecosystems can be seen only once the effects are dramatic. By that point returning the system to a desirable state will be difficult, if not impossible.”

The current study—published online in the journal Ecology Letters—focuses on models from ecology, but its findings may be applicable to other complex systems, especially ones involving human dynamics such as harvesting of fish stocks or financial markets, Hastings says.

Global climate change is already causing major environmental effects, such as changes in the frequency and intensity of precipitation, droughts, heat waves, and wildfires; rising sea level; water shortages in arid regions; new and larger pest outbreaks afflicting crops and forests; and expanding ranges for tropical pathogens that cause human illness.

U.S. presidential science adviser John Holdren (who did not participate in the UC Davis study) recently told a congressional committee: “Climate scientists worry about ‘tipping points’ … thresholds beyond which a small additional increase in average temperature or some associated climate variable results in major changes to the affected system.”

Among the tipping points Holdren listed were:

  • complete disappearance of Arctic sea ice in summer, leading to drastic changes in ocean circulation and climate patterns across the whole Northern Hemisphere;
  • acceleration of ice loss from the Greenland and Antarctic ice sheets, driving rates of sea-level increase to 6 feet or more per century;
  • ocean acidification from carbon dioxide absorption, causing massive disruption in ocean food webs.

The study was funded by the Advancing Theory in Biology program at the U.S. National Science Foundation.

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