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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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