US: Little warning for climate tipping points

As scientists around the world monitor the effects of climate change, many are on the look out for early signs of changes that might worsen the problem even further.

But new research indicates it will be difficult to spot such ecological tipping points before they happen. In fact, in some cases dramatic changes to natural systems are likely to happen with little to no warning at all.

The study by researchers from the University of California, Davis, concluded that only a limited number of ecological systems would demonstrate indicators of "regime shift" and that some natural systems were likely to show no warning signs of such dramatic change.

"Our results offer a cautionary note about the generality of forecasting sudden changes in ecosystems," co-authors Professor Alan Hastings of UC Davis and Dr Derin Wysham, now of the John Innes Centre in Norwich, England, wrote.

"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," Hastings said.

"Our new study found, unfortunately, that 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 study used models from ecology, but its findings could be applicable to other complex systems such as harvesting of fish stocks or financial markets.

A release about the research noted that US presidential science adviser John Holdren 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 the 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 six feet (two metres) or more per century; and ocean acidification from carbon dioxide absorption, causing massive disruption in ocean food webs.

The research is published in the journal Ecology Letters , in its Early View.