[extropy-chat] Save the World

[Anders Sandberg]

The Avantguardian wrote:
> Huh? I'll pass on dimming the sky on purpose. That
> will slow plant/algae growth which naturally scrubs
> CO2 from the atmosphere. Less plant growth means we
> will have to darken the skies more to compensate for
> less CO2 turnover, until we are left starving in the
> dark without solar energy. That's not the outcome I
> desire.

Does not seem likely. See Vaishali Naik, Donald J. Wuebbles, Evan H.
DeLucia and Jonathan A. Foley, Influence of Geoengineered Climate on the
Terrestrial Biosphere, Environmental Management, Volume 32, Number 3 /
September, 2003
http://www.springerlink.com/content/nffpj86jp0kfyfle/

"Abstract  Various geoengineering schemes have been proposed to counteract
anthropogenically induced climate change. In a previous study, it was
suggested that a 1.8% reduction in solar radiation incident on the
Earthrsquos surface could noticeably reduce regional and seasonal climate
change from increased atmospheric carbon dioxide (CO2). However, the
response of the terrestrial biosphere to reduced solar radiation in a
CO2-rich climate was not investigated. In this study, we hypothesized that
a reduction in incident solar radiation in a Doubled CO2 atmosphere will
diminish the net primary productivity (NPP) of terrestrial ecosystems,
potentially accelerating the accumulation of CO2 in the atmosphere. We
used a dynamic global ecosystem model, the Integrated Biosphere Simulator
(IBIS), to investigate this hypothesis in an unperturbed climatology.
While this simplified modeling framework effectively separated the
influence of CO2 and sunlight on the terrestrial biosphere, it did not
consider the complex feedbacks within the Earthrsquos climate system. Our
analysis indicated that compared to a Doubled CO2 scenario, reduction in
incident solar radiation by 1.8% in a double CO2 world will have
negligible impact on the NPP of terrestrial ecosystems. There were,
however, spatial variations in the response of NPP-engineered solar
radiation. While productivity decreased by less than 2% in the tropical
and boreal forests as hypothesized, it increased by a similar percentage
in the temperate deciduous forests and grasslands. This increase in
productivity was attributed to a sim1% reduction in evapotranspiration in
the Geoengineered scenario relative to the Doubled CO2 scenario. Our
initial hypothesis was rejected because of unanticipated effects of
engineered solar radiation on the hydrologic cycle. However, any
geoengineering approaches that reduce incident solar radiation need to be
thoroughly analyzed in view of the implications on ecosystem productivity
and the hydrologic cycle.

Keywords  Climate change - Geoengineering - Solar radiation - Terrestrial
Biosphere - Net primary productivity - Evapotranspiration"

-- 
Anders Sandberg,
Oxford Uehiro Centre for Practical Ethics
Philosophy Faculty of Oxford University