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7 Tipping Points That Could Transform

Earth

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Wired Science News for Your Neurons

7 Tipping Points That Could Transform

Earth By Brandon Keim December 23, 2009 | 12:40 pm | Categories: Earth Science, Environment

When the Intergovernmental Panel on Climate Change issue its last report in 2007,environmental tipping points were a footnote. A troubling footnote, to be sure, but thescience was relatively new and unsettled. Straightforward global warming was enough toworry about.

But when the IPCC meets in 2014, tipping points or tipping elements, in academic

vernacular will get much more attention. Scientists still disagree about whichplanetary systems are extra-sensitive to climate shifts, but the possibility cant be ignored.

The problem with tipping elements is that if any of them tips, it will be a realcatastrophe. None of them are small, said Anders Levermann, a climate physicist at thePotsdam Institute for Climate Impact Research in Germany.

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stabilize the ice,wrote Max Planck Institute meteorologist Dirk Notz inPNAS. Thoughmost of the ice will disappear during summer, much of it will re-freeze in the winter.Arctic sea ice loss is likely to be reversible if the climate were to become cooler again.

But Notz is less optimistic about Antarctic sea ice, its undersides heated by eddying

Southern Ocean currents. And the West Antarctic and Greenland ice sheets have shrunksuddenly at least twice in the last several million years, a behavior thats backed up byclimate models. Its well possible that a tipping point exists for a possible collapse forthose sheets, wrote Notz. It could render the loss of ice sheets and the accompanyingsea-level rise unstoppable beyond a certain amount of warming.

Image: NASA.

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Amazon Rainforest

As one of Earths great carbon sinks, the replacement of Amazon jungles with savannahor forest would drastically accelerate global warming.

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On their own, rising temperatures and changing weather patterns would not trigger jungledieback, wrote researchers led by Oxford University ecosystem scientist YadvinderMalhi inPNAS. But deforestation combined with intensified dry seasons leaves forestsvulnerable to fire, producing more weather-altering deforestation.

The dieback of the forests of East Amazonia in the 21st century is far from inevitablebut remains a distinct possiblity, they wrote.

Image: NASA.

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Bodl Depression, Chad

Winds whipping across the Bodl, a 10,000 square mile Saharan plain covered byancient lakebed sediments, carry 700,000 tons of dust into the atmosphere annually. Itfloats around the world, blocking sunlight and lowering temperatures in some regions,and causing rain and warming in others. Saharan dust influences Atlantic ecosystems,Caribbean coral reefs and the Amazon. Its full effects are unknown.

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Small atmospheric changes could profoundly alter the behavior of this feature, wroteRichard Washington, a specialist in African weather African weather specialist at OxfordUniversity, and colleagues inPNAS.

At one point in the last 10,000 years, dust ceased to flow altogether from the Bodl.

That doesnt seem to be our problem. Although subject to a great deal of uncertainty,some simulations of the 21st century indicate the potential for a substantial increase indust production, wrote the researchers.

Image: NASA.

South Asian Monsoons

Hundreds of millions of people depend on regular monsoon rains to nourish their crop,but the monsoons are historically capricious. In what is now India and China, theyvehave changed abruptly several times since the Last Ice Age ended.

Levermanns studies suggest that monsoon systems amplify themselves. Rainfall releasesheat, fueling winds that pull more moisture from the seas, producing more rainfall. Smallchanges can swell monsoons, or nip them in the bud.

The model is limited, but its simulations track with history. We have a long paleorecordfor precipitation, and you see that there was almost a switch. The monsoon was either on,or it was off, with very little in between, said Levermann. Climate change can flip theswitch, but its not the only cause. If you turn a forest into a desert, it reflects more

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sunlight and makes it cooler. Strong air pollution reflects sunlight, and can trigger anevent. Both exist in Indian and Chinese regions.

Image:flickrohit/Flickr.

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The Gulf Stream

Formally known as the Atlantic meridional overturning circulation, or AMOC, the GulfStream starts in the Gulf of Mexico and follows the eastern contour of North Americabefore flowing to northern Europe and western Africa. Sudden slowdowns in the

circuation occurred repeatedly during the last Ice Age. They were associated with largeand abrupt changes in surface climate, wrote Potsdam Institute climatologists MatthiasHofmann and Stefan RahmstorfinPNAS

Argument exists over whether slowdowns are primarily wind-driven, or could be causedby an influx of fresh water from melting ice sheets. In its last report, the IPCC put the riskof Gulf Stream slowdown during the 21st century at 10 percent. The true figure could be

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higher, or lower. Model deficiences make a risk assessment for AMOC changes verydifficult at present and require urgent research attention, wrote Hofmann and Rahmstorf.

Image: Models showing AMOC weakening from fresh water influx/National Center for

Atmospheric Research

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Seafloor Methane

Between 700 trillion and 10,000 trillion tons of methane hydrate, a powerful greenhousegas, are trapped in the seafloor sediments where theyve accumulated over millions ofyears. If the planet heats by 5.4 degrees Fahrenheit, well within the range of warmingpossible if greenhouse gas pollution levels remain high, seafloors could heat enough torelease a small but significant fraction of the gases.

Methane bubbling slowly into the atmosphere could raise planetary temperatures by a fulldegree Fahrenheit for as much as 10,000 years. According to researchers led byUniversity of Chicago geoscientist David Archer, methane-caused warming would persisteven if fossil fuel emissions subsided.

The modeling of methane hydrate is frankly in its infancy, but it seems robust toconclude that mankind could melt a significant fraction of the methane hydrates in theocean, they wrote.

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Image: Methane plumes rising from the Arctic Ocean floor/National OceanographyCentre, Southampton.

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The Future

What features establish the identity of a face; what distortions erase that identity beyondrecognition? asked Hans Schellnhuber, director of the Potsdam Institute for ClimateResearch and climate change advisor to German chancellor Angela Merkel, inPNAS.

By Earths face, Schellnhuber means the environmental conditions that prevailed for

most of the last several thousand years. If theres one dominant theme to the tippingelement reviews, its that Earths face is prone to what he calls singulartransformations. Theyve happened before.

Whether they will happen again, with mankind on board, is the cardinal question ofearth systems analysis [and] sustainability science, wrote Schellnhuber.

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How admittedly uncertain models should influence international climate policy is anopen question. Levermann counsels caution.

If you entered a plane and the captain said into the speaker, Theres a 10 percent chancethis plane will crash, you wouldnt stay in it, said Levermann. This is the framework

we have to think about when we talk about tipping elements.

Image: An ensemble of global temperature predictions contained in the last IPCCreport/IPCC.

See Also:

Scientists Seek Warning Signs for Catastrophic Tipping Points 9 Environmental Boundaries We Dont Want to Cross Mediterranean Is Scary Laboratory of Ocean Futures Could Methane Trigger a Climate Doomsday Within a Human Lifespan

How to Slow Climate Change for Just $15 Billion

Citations: Tipping elements in the Earth System. By Hans Joachim Schellnhuber.Proceedings of the National Academy of Sciences, Vol. 106 No. 49, December 8, 2009.

Dust as a tipping element: The Bodl Depression, Chad. By Richard Washington,Christel Bouet, Guy Cautenet, Elisabeth Mackenzie, Ian Ashpole, SebastianEngelstaedter, Gil Lizcano, Gideon M. Henderson, Kerstin Schepanski, and Ina Tegen.Proceedings of the National Academy of Sciences, Vol. 106 No. 49, December 8, 2009.

Basic mechanism for abrupt monsoon transitions. By Anders Levermann, Jacob

Schewe, Vladimir Petoukhov, and Hermann Held. Proceedings of the National Academyof Sciences, Vol. 106, No. 49, December 8, 2009.

On the stability of the Atlantic meridional overturning circulation. By MatthiasHofmann and Stefan Rahmstorf. Proceedings of the National Academy of Sciences, Vol.106 No. 49, December 8, 2009.

The future of ice sheets and sea ice: Between reversible retreat and unstoppable loss.By Dirk Notz. Proceedings of the National Academy of Sciences, Vol. 106 No. 49,December 8, 2009.

Ocean methane hydrates as a slow tipping point in the global carbon cycle. By DavidArcher, Bruce Buffett, and Victor Brovkin. Proceedings of the National Academy ofSciences, Vol 106. No. 49, December 8, 2009.

Exploring the likelihood and mechanism of a climate-change-induced dieback of theAmazon rainforest. By Yadvinder Malhi, Luiz E. O. C. Arago, David Galbraith, ChrisHuntingford, Rosie Fisher, Przemyslaw Zelazowski, Stephen Sitch, Carol McSweeney,

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and Patrick Meir. Proceedings of the National Academy of Sciences, Vol. 106 No. 49,December 8, 2009.

Brandon Keims Twitterstream and reportorial outtakes; Wired Science onTwitter.Brandon is currently working on a book about ecosystem and planetary tipping points.

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