Jökull - 01.01.2005, Síða 5

Global Warming: Take Action or Wait?
Figure 3. An air photo taken over an
area of low cloud cover off the west
coast of the U.S. The bright streaks
are produced by cloud condensa-
tion nuclei delivered to the clouds
with the smoke from the stacks of
ships passing beneath. – Á loftmynd
af hafinu við vesturströnd Banda-
ríkjanna má greina sérkennileg,
línulaga ský sem myndast vegna
rakaþéttingar á svifryki úr útblæstri
skipa.
tree leaves... By contrast, the CO2 we produce will be
removed only on a century time scale. A second rea-
son is that, as aerosols pose a medical hazard, their
production in urban environments will certainly be
curtailed. So, in the end, CO2 will win out!
COMPUTER SIMULATIONS
If one accepts the simulations generated by models,
then a doubling of CO2 will certainly result in ma-
jor climate changes which will impact virtually every
human activity and cause a major shift in the habi-
tat available to wildlife. But, as every climate scien-
tist admits, major uncertainties surround these predic-
tions. In order to assess the possible biases created
by these parameterizations, a group of scientists in
the United Kingdom undertook an elaborate exercise
designed to evaluate the sensitivity of the models to
the selection of the values adopted for the many re-
quired parameters (Stainforth et al., 2005). To this
end, they made thousands of model runs for doubled
CO2 employing all combinations of the permissible
range of values for each of these parameters. This ex-
ercise yielded a range of results which were strongly
skewed toward warmings greater than that obtained
using the usual set of parameters. Further, none of the
runs yielded warmings of less than 1.5◦C. This exer-
cise suggests that model simulations more likely un-
derestimate the impacts of increased CO2 than over-
estimate them.
Seemingly, the obvious way to test the reliability
of these simulations is to determine whether they cor-
rectly reproduce the global temperature record kept by
our thermometers. Since the beginning of the Indus-
trial Revolution, the CO2 content of the atmosphere
has risen 100 parts per million (from 280 to 380).
In addition, increases in methane and other infrared-
absorbing gases provide additional greenhouse shield-
ing which nearly matches that by the excess CO2.
Hence it is as if CO2 had risen to 450 parts per mil-
lion. The models predict that such a CO2 increase
should have warmed the planet by about 1.5◦C. Has
it?
JÖKULL No. 55, 2005 5