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TEN thousand delegates of countries and
international organizations will gather on Dec. 3-14 in Bali,
Indonesia, to negotiate “a comprehensive climate change deal that
all nations can embrace,” to quote Ban Ki Moon, the UN secretary
general.
The principal document for the
conference is the latest synthesis report of the Intergovernmental
Panel on Climate Change (IPCC) that sets out the choices for
governments in order to mitigate global warming and to adapt to
climate change.
The IPCC’s recommendations are
based largely on computer models and satellite measurements.
Observational data like the Greenland ice cores, tree rings,
retreating glaciers, and ice sheets breaking off have seized the
popular imagination.
Climatologists agree that weather
is an extremely complex phenomenon that no computer model can fully
express. Since the 1960s, when the warming trend was first detected,
modeling has vastly improved but to this day is an all too simple
approximation of the dynamics of climate.
Climate models vary in their
specifics—like where rainfall might increase or where drought
might occur—but they are remarkably consistent in indicating the
overall direction of change.
These uncertainties
notwithstanding the 2,500 scientists of the IPCC are unanimous in
saying that it’s “prudent public policy” to reduce the
emission of greenhouse gases or to keep forests intact.
All of them also agree that the
CO2 in the atmosphere was put there by humans and has risen to a
level that would make global warming impossible to reverse in the
next thousand years.
However, some of them confess
that they could only guess the speed at which warming would happen.
Even the average temperature increase over, say, a century is still
a matter of debate among them.
Is CO2 the culprit? The
calculations made by NASA’s Goddard Institute of Space Studies
show that increasing concentrations of methane (CH4), nitrous oxide
(N2O), chlorofluorocarbons (CFC) in the lower atmosphere could speed
up the warming by as much as twenty years.
These are some of the reasons the
synthesis report is hedged by “may,” “could,”
“probably,” and “perhaps.”
Among the scientists of the
Goddard Institute for example there’s a divergence of views on the
effects of global warming. James Hansen, its head, maintains that
the effects of warming over the last century are consistent with his
mathematical models. Some of his colleagues demur; these effects,
they say, are not large enough to distinguish them from those
produced by natural variations in global climate.
Since no computer yet exists that
can perform the number-crunching to simulate numerically the
complexity of climate, scientists compromise by making their
calculations at widely spaced points in a three-dimensional grid,
typically about 400 kilometers between grid points.
They readily admit that this is
much too coarse a resolution to be able to decide on adaptation
countermeasures at the country level.
What the IPCC will probably
provide the delegates are analyses based on general circulation
models. These are not enough to make decisions on locations and
investments. Mitigation rather than adaptation will be the priority.
By how much and how soon should greenhouse gas emissions be cut? How
should the responsibility be distributed? How should the costs of
the adjustment be shared? These are only a few of the questions that
will be raised in Bali.
The most important is how soon
governments should act. The IPCC’s climate models do not yield
enough information on climate feedbacks, the interactions that could
hasten or delay global warming. On what will mitigation decisions be
based?
Finally, the time scale for the
response of the weather system to greenhouse warming, according to
many scientists, is influenced by the vertical movement of water in
the ocean. Most models account only for the upper levels of the sea;
they do not account for ocean currents and salinity. There’s now a
general circulation model that brings together the atmosphere and
the ocean but not in time for Bali, as far as I know.
So what do we know and not know
at this time?
We know that there’s a warming
trend that could change weather patterns.
We know that greenhouse gases in
the atmosphere is the main cause of the increase in surface
temperature.
We know that it’s not possible
to reverse global warming or the direction of climate change.
We don’t know how fast the
change would occur, nor the temperature that could change the biota
of the planet.
Are we then at the tipping point,
as Ban Ki Moon said? Yes. Despite the uncertainties, we’ve no
choice but to accept that we are at the edge of disaster.
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