Geoscience Reference
In-Depth Information
What causes this strange behavior? The basic cause is the nonlinear
reaction to stresses, as shown by the curved double-bottomed bowl. When
systems have this kind of nonlinear behavior, there is a possibility of
tipping points and bad equilibria.
Tipping points have many interesting features. To begin with, they
often have multiple outcomes or equilibria. For example, in the case of
tippy canoes and bank runs, there are good outcomes (sitting in the
canoe, and or having your money in solvent banks) and bad outcomes
(swimming in the water, or left with worthless deposits).
A second feature is that systems can tip over into bad outcomes very
quickly and unexpectedly. Indeed, abrupt climate change is sometimes
defi ned as a change in the climate state that occurs much more quickly
remarked that fi nancial crises take much longer to arrive than you
think, and then they happen much faster than you could imagine. One
of the most dangerous features of tipping points and abrupt events is
their unpredictability.
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DANGEROUS CLIMATE-CHANGE TIPPING POINTS
What are the tippy canoes of climate change? I emphasize that, like
fi nancial crises, the exact timing and magnitude of such events are of-
ten impossible to predict. They may occur rapidly and unexpectedly—or
they may not happen at all.
With that background, four global-scale tipping elements are of
particular concern:
• The collapse of large ice sheets
• Large-scale changes in ocean circulation
• Feedback processes by which warming triggers more warming
• Enhanced warming over the long run
The fi rst example is sea-level rise from abrupt melting or collapse
of the major ice sheets of Greenland and West Antarctica. These events
would have adverse consequences for the entire planet but particularly for
coastal communities, often with large population centers. Sea level might
rise in a gradual way without any abrupt events. But many specialists be-
