cbd-ts-66-en

Part I: Impacts of Climate-related Geoengineering on Biological Diversity
CHAPTER 4
POTENTIAL IMPACTS ON BIODIVERSITY OF CLIMATE
GEOENGINEERING ACHIEVED BY SUNLIGHT REFLECTION
METHODS
As summarized in Chapter 3, if anthropogenic greenhouse-gas emissions continue on current trajectories, the
resultant projected climate change will pose an increasingly severe threat to biodiversity and ecosystem services,
adding to the many factors already influencing biodiversity loss. Effective actions intended to reduce the magnitude
of future climate change would therefore be expected to reduce its impacts on biodiversity. However, such measures
may not fully achieve their intended benefits, and are also likely to have additional unintended consequences
(Figure 2.1), that may offset (or augment) their intended effects. Thus, if a proposed geoengineering approach can
be shown to be potentially feasible and effective in reducing the risks, costs and uncertainties of climate change, its
projected positive impacts need to be considered alongside any projected further impacts of the geoengineering
measure (mostly technique-specific), with their own risks, costs and uncertainties.
This chapter explores whether and how sunlight reflection methods (SRM) might be able to reduce climate-imposed
threats to biodiversity and ecosystem services, including consideration of the uncertainties of those intended,
beneficial impacts. It also examines the potential for unintended side effects of SRM. The projected positive and
negative impacts that are common to all techniques involving reduction in incoming solar irradiance (as would result
from space- or atmospheric-based SRM) are reviewed in section 4.1; technique-specific impacts for a wider range
of approaches are reviewed in section 4.2. Carbon dioxide removal (CDR) techniques are examined in Chapter 5.
Most comparisons given here are in relation to a future world where the climate has changed and is impacting
biodiversity due to inadequate efforts to reduce greenhouse-gas emissions. Limiting the future temperature increase
to 2°C will be extremely challenging, and an increase of 3 to 5°C seems much more likely if current emission
trajectories continue.
4.1 POTENTIAL IMPACTS ON BIODIVERSITY OF GENERIC SRM THAT CAUSES UNIFORM
DIMMING
4.1.1 Potential reduction in temperature and other climatic effects from uniform dimming
Studies of the potential impacts of SRM have been primarily based on computer modelling, as discussed below.
Observations of the natural world (e.g., volcanic eruptions, recent160, 161 and historical162, 163, 164) are also relevant,
since these provide precedents for temporary changes in solar irradiance reaching the Earth’s surface, of similar
order of magnitude to proposed SRM interventions.
Several models have assumed that SRM is able to cause uniform dimming to counter the climate change projected
from doubled165, 166 or quadrupled167, 168 CO2 , or for specific IPCC SRES scenarios.169 This is a useful starting point;
160 Dutton & Christy (1992).
161 Trenberth & Dai (2007).
162 Miller et al. (2012).
163 Oman et al. (2006).
164 Oman et al. (2005).
165 Caldeira & Wood (2008).
166 Jones et al. (2010).
167 Irvine et al. (2010).
168 Schmidt et al. (2012).
169 Jones et al. (2010).
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