This is a few weeks old, but I hadn't seen it in here.
http://www.wired.com/wiredscience/2009/09/earlywarnings/
Scientists Seek Warning Signs for Catastrophic Tipping Points
* By Brandon Keim
* September 2, 2009 |
* 1:48 pm |
Tipping points are found in ecosystems, economies and even bodies. But
they’re usually recognized in retrospect, when it’s too late for
anything but regret.
Now a growing body of research suggests there are telltale
mathematical signals. If scientists can figure out how to detect them,
they may be able to forecast tipping points ahead of time.
“We are repeatedly blindsided by disasters that come out of the blue.
If we had better tools for anticipating those events, we could avoid
some of them,” said Steve Carpenter, a University of Washington
ecologist and co-author of a review Wednesday in Nature.
In 1982, physicist Kenneth Wilson won a Nobel Prize for developing
equations to describe transitions that don’t happen in a linear,
easily predictable way, but are sudden and massive, such as fluids
becoming turbulent and metals becoming magnetized.
Since then, scientists have noticed similar shifts elsewhere. The
theory provides the only models that make sense of the Sahara’s sudden
flip from fertile grassland to sandy wastes some 5,500 years ago.
Exploited fish populations fluctuate wildly. Futures prices on the S&P
500 displayed telltale skewing in the year preceding the 1987 stock
market crash.
The proposition is by no means certain, but the possibility of being
able to predict these sorts of events is tantalizing.
“These are provocative possibilities. The fact that the patterns seem
to recur in so many different circumstances suggests that the
mechanisms underlying them may have universal characteristics,” said
study co-author George Sugihara, a nonlinear dynamics specialist at
the Scripps Institution of Oceanography.
The math appears to be universal. Carpenter and others suspect that
all critical transitions are preceded by the same basic patterns. The
trick is to figure out what sort of data to look for, and then how to
make sense of it.
Tip-offs for tipping points appear when the feedback loops that
normally keep complex systems at equilibrium become stressed. Too many
trees are cut down, too many cattle are turned out to graze, too many
investors sell low. The system takes longer to recover from variations
it normally weathers. Its mathematical representations become jagged
rather than smooth.
Assuming scientists can find the signals that precede these events,
and that monitoring systems can gather the necessary high-quality,
long-term data — a very big if — researchers then need to figure how
different kinds of feedback interact and where the thresholds points
are.
In a rangeland, for instance, dozens of factors are involved in
desertification, from fire intensity and grazing pressure to ambient
moisture and soil composition. One might be more relevant than another
to understanding the system’s dynamics.
“It’d be very nice if it were true that there were precursors for
tipping points in all these diverse systems. It’d be even nicer if we
could find these precursors. I want to believe it, but I’m not sure I
do,” said Steven Strogatz, a Cornell University biomathematician who
was not involved in the paper.
The difficulty of early detection is especially pronounced with
markets. Computer models can replicate their bubble-and-crash
behavior, but real markets — buffeted by political and social trends,
and inevitably responding to the very act of prediction — are much
cloudier.
“It is hard to find clear evidence of bifurcations and transitions,
let alone find an early warning system to detect an upcoming crash,”
said Cars Homme, an economic theorist at the University of Amsterdam.
The most promising evidence of useful early warning signs comes from
grasslands, coral reefs and lakes. Vegetation-pattern-based early
warning signs have been documented in several regions, and transition
theory is already being used to guide land use in parts of Australia.
The U.S. Geological Survey is currently hunting through satellite
imagery for signals of impending desertification at two sites in the
Southwest. They’ve studied desertification there by painstakingly
measuring local conditions and experimentally setting fires, removing
grasses and controlling the fall of water. But so far, the vegetation
patterns that indicated tipping points in the Kalahari haven’t shown
up here, though this may be due to poor image quality rather than bad
theory. The researchers are now looking for signals in on-the-ground
measurements of vegetation changes.
“These things aren’t going to be foolproof. There will be false
positives and false negatives, and people need to be aware of that,”
said Carpenter. “There’s still a great deal of basic research going on
to understand the indicators better. We’re still in the early days.
But why not try? The alternative is to get repeatedly blindsided. The
alternative is not appealing.”
*****
Citation: “Early-warning signals for critical transitions.” By Marten
Scheffer, Jordi Bascompte, William A. Brock, Victor Brovkin, Stephen
R. Carpenter, Vasilis Dakos, Hermann Held, Egbert H. van Nes, Max
Rietkerk & George Sugihara. Nature, Vol. 461, No. 7260, September 2,
2009.
Image: NASA. In March, researchers predicted that continued
deforestation would cause less rain to fall in the Amazon, ultimately
resulting in the rain forest’s transformation to grasslands.
Inset:
The data needed to detect ecological tipping points comes from Earth-
orbiting satellites, but the U.S. fleet isn’t up to the task.
“Global and regional monitoring systems are a long way from where they
need to be,” said University of Wisconsin ecologist Steve Carpenter.
“Earth-observing capacity in the U.S. has deteriorated badly.”
In 2007, a National Academy of Sciences report predicted the number of
U.S. satellites would drop by 40 percent over the next three years.
“There’s a train wreck coming,” said William Gail of Microsoft’s
Virtual Earth.
In April, the National Oceanic and Atmospheric Administration said it
needed $670 million to replace U.S. weather satellites, which will
start shutting down by 2014.
“The message to policymakers is that monitoring needs to improve a
lot,” Carpenter said. “ And it’s not enough to go gather the data.
Someone has to analyze it, someone has to pay attention to it. Right
now, nobody is paying attention.”
Image: Colorado State University
--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"geoengineering" group.
To post to this group, send email to [email protected]
To unsubscribe from this group, send email to
[email protected]
For more options, visit this group at
http://groups.google.com/group/geoengineering?hl=en
-~----------~----~----~----~------~----~------~--~---
