Climate is too complex for accurate predictions
19:00 25 October 2007
NewScientist.com news service
Jim Giles
http://environment.newscientist.com/article/dn12833-climate-is-too-complex-for-accurate-predictions.html
Climate change models, no matter how powerful, can never give a
precise prediction of how greenhouse gases will warm the Earth,
according to a new study.
The result will provide ammunition to those who argue not enough is
known about global warming to warrant taking action.
The analysis focuses on the temperature increase that would occur if
levels of carbon dioxide in the atmosphere doubled from pre-Industrial
Revolution levels. The current best guess for this number – which is a
useful way to gauge how sensitive the climate is to rising carbon
levels – is that it lies between 2.0 C and 4.5 C. And there is a small
chance that the temperature rise could be up to 8C or higher.
To the frustration of policy makers, it is an estimate that has not
become much more precise over the last 20 years. During that period,
scientists have established that the world is warming and human
activity is very likely to blame, but are no closer to putting a
figure on exactly much temperatures are likely to rise.
Positive feedback
It now appears that the estimates will never get much better. The
reason lies with feedbacks in the climate system. For example, as the
temperature increases, less snow will be present at the poles. Less
snow means less sunlight reflected back into space, which means more
warming.
These positive feedbacks accelerate global warming and also introduce
uncertainty into estimates of climate sensitivity, say Gerard Roe and
Marcia Baker of the University of Washington in Seattle.
What is more, they found that better computer models or observational
data will not do much to reduce that uncertainty. A better estimate of
sensitivity is the holy grail of climate research, but it is time to
"call off the quest", according to a commentary published alongside
the paper.
Deep uncertainties
That is likely to fuel attacks by critics in the oil industry and
elsewhere who argue against investing in measures like clean energy
until more is known about climate change. Others say that we need to
act even if climate sensitivity lies at the low end of the scale,
since coastal areas would still be threatened by rising seas, for
example.
Ultimately, the papers also illustrate the limits to which models,
even those produced by powerful supercomputers, can help politicians
make decisions.
"This finding reinforces not only that climate policies will
necessarily be made in the face of deep, irreducible uncertainties,"
says Roger Pielke, a climate policy expert at the University of
Colorado at Boulder, US. "But also the uncomfortable reality – for
climate modellers – that finite research dollars invested in ever more
sophisticated climate models offer very little marginal benefit to
decision makers."
Journal reference: Science (vol 318,
--
The object of life is not to be on the side of the majority but to
escape finding oneself in the ranks of the insane. -- Marcus Aurelius
Wherever I go it will be well with me, for it was well with me here, not
on account of the place, but of my judgments which I shall carry away
with me, for no one can deprive me of these; on the contrary, they alone
are my property, and cannot be taken away, and to possess them suffices
me wherever I am or whatever I do. -- EPICTETUS
Joseph R. Darancette
daranc@NOSPAMcharter.net
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