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7.5
Geoengineering
A number of geo-engineering projects have been proposed to mitigate the effects of global warming.
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These
ideas are controversial since their effectiveness is unproven and could have unwarranted side effects. Moreover,
some could only reduce temperatures and don’t address the wider implications of greenhouse gases such as
ocean acidification, less still the political and social pressures into continuing unsustainable lifestyles leading to
the release of greenhouse gases. These points accepted; it seems increasingly likely that all methods of
mitigating climate change may have to be seriously considered since the window of opportunity for mitigating
global warming by reducing greenhouse gas emissions alone may have already closed.
Two of the more interesting geo-engineering proposals uses cloud reflectivity enhancement through different
cloud seeding mechanisms. The first uses a fine seawater spray to reduce the cloud water droplet size in low
lying stratocumulus clouds and increase reflectivity in the visible spectrum. The second seeds high altitude
cirrus clouds from aircraft increasing ice crystal size and increasing outgoing longwave radiation.
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Obviously, if these methods were used to mitigate all the greenhouse effect, this would have to be kept up
relentlessly, a daunting prospect which is probably best avoided. However, this type of approach might be
appropriate for mitigating the warming from the stratospheric emission component of air travel as a stop gap
measure, since this only has a short residence time. Therefore, if any long-term solution was found to mitigating
the greenhouse effect from stratospheric emissions this could be implemented and the cloud whitening gradually
withdrawn.
Another interesting idea is to use this cloud whitening in combination with forestry growth to mitigate climate
change. The former method reduces temperatures but not CO2
,
whilst forests absorb CO2 but may increase
temperatures.
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This is because the dark surfaces of trees absorb heat more efficiently than the surrounding land
which can be covered with highly reflective snow. In combination these may be a relatively cheap method of
mitigating against at least some effects of anthropogenic forcing.
73 Salter, S.; Sortino, G.; Latham, J. (Nov 2008). "Sea-going hardware for the cloud albedo method of reversing global warming".
Philosophical transactions. Series A, Mathematical, physical, and engineering sciences 366 (1882): 3989–4006. doi:10.1098/rsta.2008.0136.
ISSN 1364-503X. PMID 18757273. edit
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David L Mitchell andWilliam Finnegan, Modification of cirrus clouds to reduce global warming, Environ. Res. Lett. 4 (2009) 045102
75 Betts, R.A. (2000) Offset of the potential carbon sink from boreal forestation by decreases in surface albedo, Nature, Volume 408, Issue
6809, pp. 187-190.
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