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Part I: Impacts of Climate-related Geoengineering on Biological Diversity
For the above reason (and because of ocean acidification effects), it is important that SRM should not be regarded
as an alternative to strong emission reductions, in order to stabilize, and preferably reduce, the levels of greenhouse
gases in the atmosphere. SRM might, however, be considered as a supplementary action.
4.2 POTENTIAL IMPACTS OF SRM ON BIODIVERSITY AT THE TECHNIQUE-SPECIFIC LEVEL
Thus far, this chapter has addressed the general effects of space- or atmospheric-based SRM on biodiversity, based
on uniform dimming; as noted, such a change in the Earth’s radiative energy budget may not be achievable in
practice. Below, the potential benefits and drawbacks associated with three specific techniques—stratospheric
aerosol injection, cloud brightening and surface albedo enhancement—are considered, on the basis that these are
the options most frequently proposed, and are each theoretically capable of counteracting either all or most of the
radiative forcing from greenhouse gases.212 Important technique-specific considerations include the height above
the Earth’s surface where the sunlight reflection occurs, and whether there may be additional physico-chemical
interactions. The potential positive and negative impacts of space-based reflectors213, 214, 215 are expected to be
similar to those theoretically indicated by models for uniform-dimming SRM described above.
4.2.1 Potential impacts on biodiversity of stratospheric aerosol injection
In addition to the positive and negative impacts of idealised SRM already described, the climatic effects of
geoengineered stratospheric sulphate aerosol will depend on where (injection altitude and locality) and how
(injection technique and timing) this technique is deployed, with significant effects of both factors on aerosol
microphysics and behaviour, including the radius, radiative impact and longevity of the aerosols.216 Furthermore,
this proposed technique could affect precipitation acidity, stratospheric ozone depletion, and the overall quantity
and quality of light reaching the biosphere, with subsequent effects on biodiversity and ecosystem services. Some,
but not all, of these unintended negative impacts might be avoided if aerosols other than sulphates were to be used
for this approach. Other particles that have been suggested include electrostatic or magnetic nano-particles,217
potentially with relatively long atmospheric lifetimes; there is also the possibility of designing a particle with
specific attributes.218 However, they might bring with them their own particular risks—together with additional
public acceptability issues.
Increased precipitation acidity
Use of sulphate aerosols for SRM would, to some degree, increase the acidity of precipitation (“acid rain”), with
consequent impacts on ecosystems. However, the size of this effect is considered to be small, since the quantities
of sulphur estimated to be needed for this form of SRM are ≤10% of the current global deposition, and possibly
as little as 1%.219 Furthermore, sulphur deposition would be more widely distributed than is currently the case
from anthropogenic sulphur emissions, and buffering processes mean than ocean acidification is unlikely to be
significantly worsened.220
212 Vaughan & Lenton (2011).
213 Seifritz (1989).
214 Angel (2006).
215 McInnes (2010).
216 Niemeier et al. (2011).
217 Keith (2010).
218 Oral presentation by Ben Kravitz at Planet under Pressure conference, London, 27 March 2012.
219 Kravitz et al. (2009).
220 Hunter et al. (2011).
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