cbd-ts-66-en

Part I: Impacts of Climate-related Geoengineering on Biological Diversity
implications for terrestrial ecosystems since this is a key parameter determining net primary production (NPP),192
with consequences for the carbon cycle193 and a wide range of biogeochemical feedbacks. P-E is also a crucial
factor for agriculture, the frequency of forest fires;194 and freshwater quantity and quality.195
SRM that aims to achieve uniform dimming could have both predictable and unknown side effects on the
atmospheric cycling of nutrients, their deposition196 and recycling processes, in soil and in the ocean. Relative to
unmitigated climate change, the recycling of soil nutrients could be expected to be slowed, since this process is
highly temperature dependent. However, it is not yet known to what degree SRM might be able to counteract the
overall changes to nutrient cycles that might occur in a high CO2 world.
4.1.3 Projected impacts of uniform dimming on species and ecosystems
Reducing temperature through deployment of idealised SRM would, if achievable, benefit those species and
ecosystems identified in Chapter 3 as being particularly vulnerable to the negative impacts of increased temperature
due to unmitigated climate change; e.g., endemic, isolated populations (“stranded” species or on islands), and
polar and mountain ecosystems. Long-lived species which are poor at adapting to climate change (e.g. non-mobile
species, such as many trees, and others that reproduce slowly), are also likely to benefit from SRM in comparison
to unmitigated climate change, as are species with temperature-regulated sex determination. However, species
that are particularly poor at adapting to climate change are also those most at risk from sudden SRM termination
(Section 4.1.5).
There are many uncertainties relating to the ability of existing species and ecosystems to adapt to living in novel
environments resulting from rapid global climate change. This is true both for a world of unmitigated climate
change (high temperatures, altered precipitation patterns, increased CO2 concentrations) and for a world where
radiative forcing due to high levels of greenhouse gases is masked by SRM (more diffuse light, altered precipitation
patterns, high CO2 concentrations).
Overall, if i) the world behaves the way that it does in most global climate models developed to date; ii) uniform
or near-uniform global dimming is achievable, and iii) there are no serious additional adverse side effects, then
SRM-induced (uniform) dimming would greatly reduce the impacts of climate change on biodiversity relative to a
high greenhouse gas world. Nevertheless, climate model predictions have their limitations (being unable to exactly
match changes in the real world, particularly at fine spatial and temporal scales, i.e. regionally and annually); and
there is inevitably some risk of unexpected, as well as unintended, side effects.
Global-scale SRM necessarily involves “unknown unknowns”, since it is unlikely that all potential risks can be
identified through smaller-scale deployments.197 Furthermore, the comparison with “unmitigated climate change”
necessarily covers a range of potential scenarios, although (as pointed out in Chapter 3) current trajectories indicate
that global warming of at least 3–5°C by 2100 is now very likely.
4.1.4 Impacts of high CO 2 under SRM
SRM does not seek to reduce the atmospheric concentrations of anthropogenic CO2, and the process of ocean
acidification will therefore continue. As a result, marine biodiversity will be increasingly exposed to the adverse
impacts of decreasing pH (Section 3.2.3). Nevertheless, there may be significant second order effects.198 One
unintended, additional negative impact would be more CO2 dissolving in the ocean if its surface temperature has
192 Zhao & Running (2010).
193 Van der Molen et al. (2011).
194 Cochrane & Laurance (2008).
195 Oki & Kanaer (2006).
196 Kravitz et al. (2009).
197 MacMynowski et al. (2011).
198 Williamson & Turley (2012).
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