| 
May 2004
Cooling
us off:
John
Latham ponders a plan to counter global warming
John Latham |
When MMM’s John Latham first
wrote about the idea of tinkering with marine clouds
to offset global warming in 1990, he faced some scorn.
Two irate readers berated John’s note on the
topic in Nature magazine, contending that society
should cut back on carbon dioxide emissions instead
of further interfering with the environment.
But with carbon dioxide levels continuing to rise
in the atmosphere, John’s research is getting
a bit more attention, as are other still-unproven
plans that seek to counter global warming.
“I was quite prepared, and still am, for
this idea to be viewed as crazy,” John concedes.
John’s idea, which has not been fully tested,
is to increase the number of water droplets in about
10% of the world’s marine stratocumulus clouds.
This could be accomplished by bolstering the number
of tiny saltwater droplets that act as cloud condensation
nuclei, meaning they would serve as centers for the
production of additional droplets.
Such a process would make the clouds whiter, increasing
their albedo, or ability to reflect solar radiation
back into space. If the clouds’ reflectivity
could be boosted by a few percent (which could be
amply achieved by doubling the droplet numbers),
this would compensate for a doubling of carbon dioxide
levels in the atmosphere and, at least in theory,
produce a cooling that would compensate for global
warming.
The plan could also have the benefit of blocking
additional sunlight by increasing the lifetimes of
the clouds. The reason is the added droplets would
be small and descend slowly. As a result, it would
take longer for them to combine into drizzle or raindrops
and fall back to Earth, dissipating the clouds.
 One theorectical approach to
whitening marine stratocumulous clouds would
be
for giant turbines to send microscopic droplets into the air, as demonstrated
by
this prototype instrument. (Photo courtesy Stephen Salter). |
John hopes to get funding to test the idea within
the next couple of years. Such tests could involve
a plane seeding marine stratocumulus clouds with
particles and then collecting data on the resulting
whitening of the clouds.
If the plan proved valid and policy makers ever
wanted to implement it, John says they would have
to overcome formidable technological challenges.
When bubbles on the ocean surface burst naturally,
they release hundreds or thousands of microscopic
droplets, many of which rise to form droplets in
low-lying marine clouds. How could such droplets
be produced artificially?
John has a few ideas, but one of his collaborators,
a Scottish inventor at the University of Edinburgh
named Stephen Salter, is working on a particularly
innovative solution. It involves designing turbines
with a height of about 70 meters (220 feet) that
would generate a saltwater spray. John says hundreds
of such turbines, powered by wind or wave energy,
could whiten the required coverage of clouds.
The amount of water involved would be surprisingly
minor: only about 10 cubic meters of ocean water
throughout the world would have to be sprayed every
second. Because the required saltwater particles
are so small—about one micron in diameter—some
1021 particles can fit it into a single cubic meter
of water. (If you’re wondering how big a
number 1021 is, it’s more than the estimated
number of grains of sand on all the world’s
beaches.)
Even if the technological challenges could be
overcome, scientists would need to make sure such
a system wouldn’t create unintended consequences.
For example, John wonders how creating cool areas
over an otherwise warm world would affect global
wind and precipitation patterns.
Despite qualms about further interfering with
nature, some experts appear open to at least exploring
plans to cool Earth. A recent symposium in England
on engineering strategies to counter global warming
included presentations on floating tiny aluminum
balloons in the stratosphere to reflect sunlight,
burying carbon dioxide in the ground or beneath
the ocean, encouraging the growth of plankton to
absorb carbon dioxide, and several other schemes.
As far-fetched as these may sound, scientists
are beginning to wonder if society will need to
take some sort of action to offset higher greenhouse
gas levels in the atmosphere—especially since
public leaders are failing to curb emissions.
“People came to the conference with a very
skeptical view,” says John, one of the presenters
at the conference, “and they came away thinking
these ideas need to be explored.” •David
Hosansky
Also in this issue...
Shielding the Pentagon
Streamlining
the NCAR Science Store
Wilmot “Bill” Hess
Short
Takes
Spring
Fling
Mentoring
Latina students
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