Jökull - 01.01.2005, Blaðsíða 3

Global Warming: Take Action or Wait?
can meet all of our energy needs for several centuries
to come. Further, it is likely to be many, many years
before any other source of energy can compete on a
large scale with coal. For example, the prime can-
didate, solar electricity, currently costs about twenty
times that produced in coal-fired plants.
Many environmentalists make the plea that the
CO2 content of the atmosphere not be allowed to ex-
ceed 450 parts per million. Realists, however, con-
tend that even with great effort, we will not be able
to prevent CO2 from reaching a concentration of 560
parts per million (i.e., double the pre-industrial level).
Pessimists, who fear that significant action will not be
taken, predict that early in the next century the con-
tent could reach 840 parts per million (i.e., triple the
pre-industrial level).
To see why an attempt to hold the atmosphere’s
CO2 content below, let’s say 560 ppm, poses a very,
very difficult challenge, let us consider the limits that
would have to be placed on the release of CO2 as the
result of fossil-fuel-use consumption. As a rule of
thumb, for each four billion tons of carbon burned,
the atmosphere’s CO2 content rises about one part per
million. Hence, were this 560 parts per million limit
to be put in place, the maximum allowable carbon
burning would be 4x(560–380) or 720 billion tons.
In an ideal world carbon allotments would be divided
among the nations of the world in proportion to their
respective populations. In this case, the world’s tradi-
tional industrialized nations would be allocated only
about 20 percent of the pie or 144 billion tons (see
Figure 2). As together these nations currently con-
sume about 6 billion tons of carbon per year, if they
maintained this pace, they would run through their al-
lotment in only 24 years!
The debate about global warming does not center
on uncertainties in the projections of the magnitude
of the CO2 rise. But rather, it centers on uncertainties
in the climatic consequences of this increase. These
consequences are based on sophisticated simulations
carried out using the world’s most powerful comput-
ers. While these simulations faithfully incorporate ev-
ery aspect of the climate system, in those cases where
the details of the physics are fuzzy, the designers are
forced to resort to empirically determined parameteri-
zations to fill in the gaps. Many of these parameteriza-
tions have to do with aspects of the hydrologic cycle
(i.e., water vapor, clouds, precipitation, sea ice).
WATER VAPOR FEEDBACK
Much of the criticism of the climatic projections pro-
duced by these simulations stems from what is re-
ferred to as “water vapor feedback.” By itself, a dou-
bling of the atmosphere’s CO2 content would warm
the planet by a modest 1.2◦C. However, as the planet
warms, the vapor pressure of liquid water will corre-
spondingly increase and consequently the atmosphere
will be able to hold more water vapor. As do CO2
molecules, H2O molecules capture outgoing earth
light (infrared rays). In all of the numerical mod-
els, the increase in atmospheric water vapor associ-
ated with a doubling of CO2 amplifies the warming by
a factor of 2 to 3 (Soden et al., 2005). Hence, 1.2 ◦C
becomes 2.4 to 3.6◦C. Further, the models yield larger
than average warming for the interiors of continents
and nearly twice the average warming for the Arctic
Ocean and its surrounding lands.
One prominent atmospheric specialist, MIT’s
Richard Lindzen, vigorously denies that this feed-
back will occur in the real world (Lindzen and Nigam,
1987). He admits that the water vapor content of trop-
ical air will rise but postulates that the air over the ex-
tra tropical desert regions will, instead, become even
drier. Because of its low water vapor content and
dearth of cloud cover, the atmosphere over the world’s
deserts acts as the primary “radiator” by which the
planet rids itself of the heat supplied by the Sun.
Hence, Lindzen envisions that, instead of amplifying
the warming produced by extra CO2, the decrease in
water vapor in these extra tropical regions will out-
weigh the increase in the tropics. The net result will
be a negative feedback reducing the small warming
produced by CO2 itself. Among atmosphere special-
ists, Lindzen stands pretty much alone in this view
and has produced no model simulations to back his
intuition. Further, as his detractors point out, Lindzen
is well known for his contrarian views. For example,
with equal vigor, he denies that cigarette smoking has
been proven to cause lung cancer.
JÖKULL No. 55, 2005 3