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From
•>>March 2006
Tom M. L. Wigley answers
a few questions about this month's fast moving front in the
field of Geosciences.
Field: Geosciences
Article: Interpretation of high projections for global-mean warming
Authors: Wigley,
TML;Raper, SCB
Journal: SCIENCE 79 2001, 293 (5529): 451-454, JUL 20 2001
Addresses:
Natl Ctr Atmospher Res, POB 3000, Boulder, CO 80307 USA.
Natl Ctr Atmospher Res, Boulder, CO 80307 USA.
Univ E Anglia, Climat Res Unit, Norwich NR4 7TJ, Norfolk, England.
Alfred Wegener Inst Polar & Marine Res, D-27515 Bremerhaven, Germany.
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Why do you think your
paper is highly cited?
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“The pathway to an acceptable future involves a difficult and delicate balancing of the benefits of reduced climate change against the costs of achieving such a reduction.”
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This paper deals with projections of future global-mean
temperature change from 1990 to 2100, due to emissions of
greenhouse gases and related substances. The projections, which
assume a future where no policies are introduced to cut back on
these emissions, are the first probabilistic projections that have
been made. We account for a range of uncertainties: in future
emissions; in the climate sensitivity; in the rate at which heat
penetrates the deep ocean; in the radiative forcing due to sulfate
aerosols; and in feedbacks on the carbon cycle.
Does it describe a new discovery or a new methodology that’s
useful to others?
We used a minor modification of the standard Latin Hypercube
Sampling method for producing probabilistic results that we call
"Exhaustive Fractile Sampling".
Could you summarize the significance of your paper in layman’s
terms?
The paper shows that, with 90% confidence, the global-mean
warming over the period from 1990 to 2100 will lie in the range of
1.7ºC to 4.9ºC with a median estimate of 3.1ºC. These are very
large changes when compared with anything that has occurred in the
past. Over the 20th century, the world warmed by around
0.6ºC to 0.7ºC. Therefore, even at the low end, the future rate
of warming is more than twice the past warming rate. These likely
future changes are of considerable concern to humanity since they
take us into uncharted climate territory.
How did you become involved in this research?
I and my co-author, Dr. Sarah Raper, have been carrying out
research into climate change (and, specifically, research into the
possible human influences on climate) since the late 1970s.
What are the social or political implications of your
research?
There is a clear policy implication of this work, as the
expected global-mean temperature in 2100, even at the low end of
the range of possibilities, exceeds anything humankind has
experienced in the past. If these calculations are reasonable,
large changes in other climate variables and in sea level will
also occur.
Qualitatively, these are not new results—but putting them in
a probabilistic framework allows a better estimate of the risks
involved in the absence of policies to reduce future warming. To
do so requires reducing emissions of greenhouse gases eventually
to levels well below the current levels—and, since CO 2
is the primary anthropogenic greenhouse gas, this requires either
reducing our dependence on fossil fuels as an energy source or
devising ways to sequester most of the CO2
that is released by fossil fuel burning.
The ultimate objective is stated in the UN Framework Convention
on Climate Change—namely, to stabilize the concentrations of
greenhouse gases at a level that will avoid dangerous interference
with the climate system (a benefit), but also avoid serious
disruption of the global economy (a cost). The pathway to an
acceptable future involves a difficult and delicate balancing of
the benefits of reduced climate change against the costs of
achieving such a reduction.
Tom M.L. Wigley,
Senior Scientist,
National Center for Atmospheric Research,
Boulder, CO, USA
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