Geoscience Reference
In-Depth Information
engineering is generally divided into two categories: First are tech-
niques that remove CO
2
from the atmosphere; second are solar radiation
In this section, I consider the second option of solar radiation manage-
ment, while the option of CO
2
removal, which is genuinely attractive, is
postponed to later chapters.
The principle underlying solar radiation management is to slow or
reverse warming by changing the energy balance of the earth. You can
think of the process as making the earth “whiter” or more refl ective, so
that less sunlight reaches the surface. This cooling effect will offset the
warming that comes from the accumulation of CO
2
in the atmosphere.
The whitening process is similar to changes that occur after large
volcanic eruptions. After Mount Pinatubo blasted 20 million tons of
particles into the stratosphere in 1991, global temperatures fell by about
0.4°C. Geoengineering can be viewed as creating artifi cial volcanic erup-
tions, and fi ve or ten artifi cial Pinatubo eruptions might need to be created
every year to offset the warming effects of CO
2
accumulation.
In recent years there have been many proposals for geoengineering
through solar radiation management. Some involve literally making the
earth whiter (say, by using white roofs and roads). Perhaps the easiest to
visualize is putting millions of little mirror-like particles 20 miles above
the earth. For example, we might artifi cially increase sulfate aerosols in
the stratosphere above background levels. This would increase the plan-
etary albedo or whiteness and reduce incoming solar radiation. Climate
scientists have calculated that refl ecting about 2 percent of solar output
could offset the warming effect of a doubling of CO
2
. The right number
of particles in the right place could reduce solar radiation and cool the
earth by the desired amount.
Cost estimates indicate that, if successful, geoengineering is likely
to be much less expensive than reducing CO
2
emissions. Current esti-
mates are that geoengineering would cost between one-tenth and one-
hundredth as much as reducing CO
2
emissions for an equivalent amount
of cooling. In economic terms, it is useful to view geoengineering as
essentially costless. The major issues connected with this approach re-
volve around its effectiveness and its side effects.
