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By Katie Greene - Stanford University News
Trading
greenhouse gas emissions is one of the most contentious
issues in the global climate debate. Countries hope to wiggle
out of costly carbon dioxide emission cuts by decreasing
the amount of other important greenhouse gases spewed into
the atmosphere. In an April 5 letter to Nature, two researchers
at Stanford and EPRI used a computer model to evaluate the
most cost-effective way to trade off among the varied zoo
of greenhouse gases.
``President
Bush may have rejected the Kyoto protocol, but the problem
of climate change is not going to go away,`` said Alan S.
Manne, professor emeritus of operations research at Stanford.
``Something has to be done about greenhouse gas emissions.``
Economists
want to cut back on greenhouse gases in the cheapest, most
cost-effective way. They want to be able to shift the focus
away from carbon dioxide if reducing an equivalent amount
of methane would be cheaper and just as effective.
But
teasing out equivalence between gases is an apples-and-oranges
comparison. A greenhouse offender such as methane may trap
heat more efficiently than carbon dioxide, but in the rough-and-tumble,
molecule-eat-molecule atmospheric environment, methane survives
only a fleeting few decades, while other gases, such as
the hardier carbon dioxide and smog-related nitrous oxide,
hang around for more than a century. And carbon dioxide,
even though it is not a particularly effective planet-warmer
on a molecule-by-molecule basis, is pumped into the atmosphere
in such huge amounts that it may contribute up to 75 percent
of the estimated warming, experts say.
Figuring
out a fair swap of methane for carbon dioxide or nitrous
oxide isn`t straightforward. The writers of the Kyoto protocol
decided to define tradeoffs with a quantity called the ``global
warming potential,`` or GWP. The GWP characterizes the amount
of heat that a certain amount of gas will trap from now
until a designated time in the future.
Economists
have been fretting over global warming potentials ever since
the idea was introduced in 1990, Manne said. Global warming
potentials don`t consider damages that could stem from global
warming such as property damage from increased flooding
or the loss of crops. Nor do they take into account the
money companies will spend - or lose - as they reduce their
emissions.
Manne
and co-author Richard Richels of EPRI proposed an alternative
to the GWP in the Nature letter.
``This
paper by Manne and Richels clearly illustrates the serious
limitations of the currently proposed method and skillfully
demonstrates the advantages of some workable alternatives,``
said John Weyant, director of the Energy Modeling Forum
at Stanford.
Manne
and Richels`s first step is to agree on a damage limit -
a restraint on the amount of havoc global warming will be
allowed to wreak. Right away, problems crop up.
``The
trouble is that these damages can be difficult to quantify,``
Manne said. ``It`s easy in agriculture and forestry, where
you can track the price of potatoes or lumber, but when
you come to ecological values and ecological systems, it
becomes very debatable how much an otter is worth.``
To get
around this complication, Manne suggests setting a concrete
goal, such as limiting the global temperature change that
occurs by 2100 to 3 degrees. ``You reach more agreement
if you list the temperature change you want to maintain,``
he said. Temperature change is a reasonable barometer for
damages, Manne said, because researchers link temperature
with the rise in sea level, changes in weather patterns
and the spread of tropical diseases.
Next,
the researchers plug the goal into a computer model named
MERGE (for Model for Evaluating the Regional and Global
Effects of greenhouse gas reduction policies) and let the
model determine the cheapest way to make that goal a reality.
MERGE performs three major functions: It calculates the
atmospheric warming due to different gas combinations, it
evaluates emission tradeoffs between nine political regions,
and it considers economic factors such as the need for electricity
and the business costs of new technology and lost productivity.
The
model doesn`t exactly spit out a portfolio of gases perfectly
tuned to give the winning combination. It does, however,
describe how the cost-effectiveness of reducing gases other
than carbon dioxide goes up or down as a goal deadline approaches.
In a
nutshell, unless the deadline is imminent, reducing methane
doesn`t really make much sense given its short lifetime
in the atmosphere, Manne said. Cutting back on longer-lived
gases (like carbon dioxide and nitrous oxide) would be more
effective in the long run.
And
it`s the long-term solutions - like new technologies plus
a carbon-emissions tax that increases with time - that economists
favor, Manne said. ``Kyoto means that the U.S. economy would
take a big hit in the next 10 years,`` he said.
``The
evaluation of short- versus long-lived greenhouse gases
is something that`s got to be faced,`` Manne said. ``The
people who put together Kyoto didn`t have many alternatives,
and when they decided on global warming potentials they
knew it was a shortcut. They wanted to end the argument.
But it doesn`t end the argument.``
MERGE
Project: http://www.stanford.edu/group/MERGE/
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