Quick Fix for Global Warming?
(Top Posts - Science - 060507)

- - -
15:35 05 June 2007

NewScientist.com news service
Catherine Brahic
- - -

Excerpts [with inserts, not part of orig-
inating article, in brackets]:

A solar shield that reflects some of the
Sun's radiation back into space would
cool the climate within a decade and
could be a quick-fix solution to climate
change, researchers say.

Because of their rapid effect, however,
they should be deployed only as a last
resort when "dangerous" climate change
is imminent, they warn.

Solar shields are not a new idea - such
"geoengineering" schemes to artificially
cool the Earth's climate are receiving
growing interest, and include proposals
to inject reflective aerosols into the stra-
tosphere, deploying space-based solar
reflectors and large-scale cloud seeding.

The shields are inspired by the cooling
effects of large volcanic eruptions that
blast sulphate particles into the stratos-
phere. There, the particles reflect part
of the Sun's radiation back into space,
reducing the amount of heat that reaches
the atmosphere, and so dampening the
greenhouse effect.



Ken Caldeira at the Carnegie Institution
of Washington, in California, US, and
Damon Matthews at Concordia Univer-
sity, Canada, used computer models to
simulate the effects that a solar shield
would have on the Earth's climate if
greenhouse gas emissions continued
to rise along a "business as usual" sce-

- - -
[of note, many measures can be taken
to reduce greenhouse emissions, and
hopefully, those measures will be taken
and will reduce emissions, rather than
doing nothing and allowing emissions
to rise as they have been]
- - -

"We have been trying to pinpoint the
one really bad thing that argues against
geoengineering the climate," says Cal-
deira. "But it is really hard to find."

His computer models simulated a gra-
dually deployed shield that would com-
pensate for the greenhouse effect of
rising carbon dioxide concentrations.

By the time CO2 levels are double
those of pre-industrial times - predict-
ed to be at the end of the 21st century -
the shield would need to block 8% of
the Sun's radiation.

- - -
[of note, many scientists warn that with
a 'business as usual' approach, CO2
levels will be far greather than double
far sooner than the end of the 21st cen-
- - -

The researchers found that a sulphur
shield could act very quickly, lowering
temperatures to around early 20th-cen-
tury levels within a decade of being

"The trouble is, the decadal timescale
works both ways," says Caldeira. A sul-
phate shield would need to be contin-
uously replenished, and the models
show that failing to do so would mean
the Earth's climate would suddenly be
hit with the full warming effect of the
CO2 that has accumulated in the mean-

"So if you have the shield up there and
it fails ... then you effectively compress
into a decade or two the warming that
would have happened while the shield
was up," Caldeira explains.


"Personally, as a citizen not a scientist,
I don't like geo-engineering because
of the high environmental risk," Caldeira
told New Scientist. "It's toying with poorly
understood complex systems."

And the ease with which they could work
is also risky, he says: "These schemes
are almost too cheap and easy. Just one
fire hose spraying sulphur dioxide into
the atmosphere would do the job for a
century. That would cost about $100
million - nothing in comparison to the
hundreds of billions it would take to
transform our energy supply."

But he also believes it is time to consider
solar shields seriously. On 1 June, James
Hansen, head of NASA's Institute for
Space Studies in the US, published a
paper stating that Earths' climate system
has reached a tipping point.


Hansen's study suggests that only mod-
erate additional warming is likely to trig-
ger the disintegration of the west Ant-
arctic and Arctic ice sheets - events
which would be near-impossible to re-


He says that if forced to consider deploy-
ing a solar shield, "we would need to be
confident that we would not be creating
bigger problems than we are solving."


Climate Change - Want to know more
about global warming: the science, im-
pacts and political debate? Visit our
continually updated special report.

- - - end excerpts - - -