Climate change: are we past the point of no return?

May 23, 2009

Climate change won’t be a smooth transition, warn Allianz and WWF in a report flagging potentially catastrophic ecological tipping points.

Article at a glance

  • Small climate changes can make very big differences
  • Report focused on 12 key tipping elements at risk
  • Possible half meter sea level rise by 2050
  • Report more positive on melting permafrost

We tend to think of climate change as a slow and steady process, following a fairly predictable, even manageable path. That is a mistake, warns the 'Tipping Points Report' published by Allianz and WWF

With global warming a smooth transition is unlikely, says the report. Instead there may be disruptive, sudden changes as key ecological thresholds, or tipping points, are breached.

As report co-author Tim Lenton describes in the film below, tipping points describes the concept that “a small change can make a big difference” to a particular part of the Earth’s ecosystem, changing its state fundamentally.

Such transitions may be irreversible. In some cases, passing the tipping point is barely perceptible, but it still makes a large impact on the future.

The term "tipping element" describes those environmental processes that could be forced past a tipping point. The report focuses on 12 of the most urgent or “policy-relevant” tipping elements where human activity could have a decisive influence. The elements fall into three categories:

  • melting ice and permafrost
  • climate phenomena like El Nino and the ‘Gulf Stream’ that influence other elements
  • changing rainfall patterns in the tropics and sub-tropics

The report then identifies four sets of risks associated with these elements and the impacts they entail.

  • sea level rise
  • unstable monsoon in India
  • drought in Amazonia
  • drought in Southwest North America

Points of no return?

The best known tipping point is the global warming threshold of 2 degrees Celsius. A temperature rise slightly above that is considered highly dangerous by climate scientists. It could, for instance, trigger dieback of much of the Amazon rainforest, destroying a vital carbon sink and source of fresh water.

Sea level rises, unpredictable monsoons in India, and the desertification of the Southwest region of North America are other key tipping points, according to the report’s authors from the Tyndall Centre for Climate Change Research.

In the Southwestern US the tipping point has probably already been passed. The scientists now predict that by mid-century levels of aridity last seen in the 1930s will be the norm.

The study suggests melting polar ice sheets would make possible a 0.5 meter sea level rise by 2050. The Greenland ice sheet, for example, contains enough water for up to 7 meters of global sea level rise. With 1 to 4 degrees of global warming above 1980-1999 levels it could tip into irreversible meltdown. While a total meltdown would take several hundred years, half a meter’s worth of melt this century is possible.

A global half-meter sea level rise would almost double the number of people vulnerable to flooding worldwide, two thirds of them in Asia. It would endanger an extra $3 trillion of coastal assets, mostly in China, the US, and India. In New York, the exposed assets would increase by 23%.

In some cases the report offers more reassurance.

Permafrost melt in Eastern Siberia could release greenhouse gases CO2 and methane. But it would require an extreme 9 degrees Celsius surface warming for the system to tip. Claims that the release of greenhouse gases trapped in the permafrost will lead to runaway global warming are “grossly exaggerated,” the authors conclude. 

Regional extremes

Unfortunately, tipping points are largely absent from policymaking discussions and not well reflected in current climate change policies.

For instance, by framing policy on a global scale—the 2 degrees threshold for example—we forget that regional climate changes may be far more extreme.

We may also be overly dependent on reports from the Intergovernmental Panel on Climate Change (IPCC) which have in some cases been challenged by more recent evidence (see 'Polar expert brands climate change report “complacent”').

And because there has been no concerted effort to reduce carbon emissions we are almost certain to breach the 2 degrees threshold this century. The climate change lag effect means that we could already be irrevocably committed to tipping points we don’t even know about yet

James Tulloch

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