19.5.4.
Risks from Geoengineering (Solar Radiation Management)
Geoengineering
refers to a set of proposed methods and technologies that aim to alter the
climate system at a large scale to alleviate the impacts of climate change
(WGII Glossary; IPCC, 2012b; AR5 WGI Sections 6.5 and 7.7; WGIII Chapter 6).
The main intended benefit of geoengineering would be the reduction of climate
change that would otherwise occur, and the associated reduction in impacts
(Shepherd et al., 2009). Here we focus on risks, consistent with the goal of
this chapter. Although geoengineering is not a new idea (e.g., Rusin and Flit,
1960; Budyko and Miller, 1974; Enarson and Morrow, 1998, and a long history of
geoengineering proposals as detailed by Fleming, 2010), it has received
increasing attention in the recent scientific literature.
Geoengineering
has come to refer to both carbon dioxide removal (CDR, discussed in detail in
AR5 WGI Section 6.5, FAQ 7.3) and solar radiation management (SRM; Shepherd et
al., 2009; Lenton and Vaughan, 2009; Izrael, 2009; discussed in detail in AR5
WGI, Section 7.7, FAQ 7.3). These distinct approaches to climate control raise very
different scientific (e.g., Shepherd et al., 2009), ethical (Morrow et al.,
2009; Preston, 2013) and governance (Lloyd and Oppenheimer, 2013) issues. Many
approaches to CDR are considered to more closely resemble mitigation rather
than other geoengineering methods (AR5 WGI, Chapter 6.5; IPCC, 2012b). In
addition, CDR is thought to produce fewer risks than SRM if the CO2 can be
stored safely (AR5 WGI Section 6.5; Shepherd et al., 2009) and unintended
consequences for land use, the food system and biodiversity can be avoided
(19.4.3). For these reasons, in addition to the more substantial recent
literature on SRM’s potential impacts, we only address SRM in this section. SRM
is a potential key risk because it is associated with impacts to society and
ecosystems that could be large in magnitude and widespread. Current knowledge
on SRM is limited and our confidence in the conclusions in this section is low.
Studies of
impacts on society and ecosystems have been based on two of the various SRM
schemes that have been suggested: stratospheric aerosols and marine cloud
brightening. These approcaches in theory could produce large-scale cooling
(Salter et al., 2008; Lenton and Vaughan, 2009), although it is not clear that
it is even possible to produce a stratospheric sulphate aerosol Layer
sufficinently optically thick to be effective (Heckendorn et al., 2009; English
et al., 2012). Observations of volcanic eruptions, frequently used as an
analogue for SRM (Robock et al., 2013), indicate that while stratospheric
aerosols can reduce the global average surface air temperature, they can also produce
regional drought (e.g., Oman et al., 2005; Oman et al., 2006; Trenberth and
Dai, 2007), cause ozone depletion (Solomon, 1999), and reduce electricity
generation from solar generators that use focused direct sunlight (Murphy,
2009). Climate modeling studies show that the risk of ozone depletion depends
in detail on how much and when stratospheric aerosols would be released in the
stratosphere (Tilmes et al., 2008) and find that global stratospheric SRM would
produce uneven surface temperature responses and reduced precipitation (Schmidt
et al., 2012; Kravitz et al., 2013), weaken the global hydrological cycle (Bala
et al., 2008), and reduce summer monsoon rainfall relative to current climate
in Asia and Africa (Robock et al., 2008). Hemispheric geoengineering would have
even larger effects (Haywood et al., 2013).
The net
effect on crop productivity would depend on the specific scenario and region
(Pongratz et al., 2012). Use of SRM also poses a risk of rapid climate change
if it fails or is halted suddenly (AR5 WGI Section 7.7; Jones et al., 2013),
which would have large negative impacts on ecosystems (Russell et al., 2012;
high confidence) and could offset the benefits of SRM (Goes et al., 2011).
There is also a risk of “moral hazard;” if society thinks geoengineering will
solve the global warming problem, there may be less attention given to
mitigation (e.g., Lin, 2013). In addition, without global agreements on how and
how much geoengineering to use, SRM presents a risk for international conflict
(Brzoska et al., 2012). Since the direct costs of stratospheric SRM have been
estimated to be in the tens of billions of US dollars per year (Robock et al.,
2009; McClellan et al., 2012), it could be undertaken by non-state actors or by
small states acting on their own (Lloyd and Oppenheimer, 2012), potentially
contributing to global or regional conflict (Robock, 2008a; Robock, 2008b).
Based on magnitude of consequences and exposure of societies with limited
ability to cope, geoengineering poses a potential key risk.
---------------------------
WGII AR5 Final Drafts (accepted).
Ch 20 — Climate-resilient pathways: adaptation, mitigation, and sustainable development
Box 20-4.
Considering Geoengineering Responses
If climate
change mitigation leads to socially unacceptable pain and distress,
policymakers may be faced with
demands to
find further ways to reduce climate change and its effects.
Such
options include intentional large-scale interventions in the earth system
either to reduce the sun’s radiation that reaches the
surface of the earth or to increase the uptake of carbon dioxide from the
atmosphere. An example of the former is
to inject sulfates into the stratosphere. Examples of the latter include
facilities to scrub carbon dioxide from the
air and chemical interventions to increase uptakes by oceans, soil, or biomass
(UK Royal Society, 2009; Chapter 19;
IPCC Working Group III: Chapter 6; and Working Group I, Chapters 6 and 7).
Discussions
of geoengineering have only recently become an active area of discourse in
science, despite a longer history of
efforts to modify climate (Schneider, 1996, 2009; Keith, 2000; Crutzen, 2006).
Many of the possible options are
known to be technically feasible, but their costs, effectiveness, and
side-effects are exceedingly poorly understood
(NRC, 2010b; MacCracken, 2011; Vaughan and Lenten, 2011; Goes et al., 2011).
For example, some interventions
in the atmosphere might not be unacceptably expensive in terms of direct costs,
but they might affect the
behavior of such earth system processes as the Asian monsoons (Robock et al.,
2008; Brovkin et al., 2009).
Some
interventions to increase carbon uptakes, such as scrubbing carbon dioxide from
the earth’s atmosphere, might be socially
acceptable but economically very expensive. Moreover, it is possible that
optimism about geoengineering
options might invite complacency regarding mitigation efforts.
In any
case, implications for sustainable development are largely unknown. Even though
some views have been expressed
that geoengineering is needed now in order to avoid irreversible impact such as
the loss of ocean corals (while many
governments have not begun to consider it at all), several countries consider
it a research priority rather than a
current decision-making option (NRC, 2010b). The challenge is to understand
what geoengineering options would do to
moderate global climate change and also to understand what their ancillary
effects might be. This would allow
policymakers in the future to respond if severe disruptions appear and, as a
result, there is a need to consider rather
dramatic technology alternatives. Some observers propose that research efforts
should include limited experiments
with geoengineering options, but agreement has not been reached about criteria
for determining what experiments
are appropriate or ethical (e.g., Blackstock and Long, 2010; Gardiner, 2010).
----------------------------
WGII AR5
Glossary
Geoengineering
Geoengineering
refers to a broad set of methods and technologies that aim to deliberately
alter the climate system in order to
alleviate the impacts of climate change. Most, but not all, methods seek to
either (a) reduce the amount of absorbed
solar energy in the climate system (Solar Radiation Management) or (b) increase
net carbon sinks from the atmosphere
at a scale sufficiently large to alter climate (Carbon Dioxide Removal). Scale
and intent are of central importance.
Two key characteristics of geoengineering methods of particular concern are
that they use or affect the climate
system (e.g., atmosphere, land, or ocean) globally or regionally and/or could
have substantive unintended effects
that cross national boundaries. Geoengineering is different from weather
modification and ecological engineering,
but the boundary can be fuzzy (IPCC, 2012b, p. 2).
Links to IPCC report:
Chapter 19. Emergent Risks and Key Vulnerabilities
http://ipcc-wg2.gov/AR5/images/uploads/WGIIAR5-Chap19_FGDall.pdf
Chapter 19. Emergent Risks and Key Vulnerabilities
http://ipcc-wg2.gov/AR5/images/uploads/WGIIAR5-Chap19_FGDall.pdf
WGII AR5
Final Drafts (accepted).
Ch 20 —
Climate-resilient pathways: adaptation, mitigation, and sustainable development
Glossary
WORKING GROUP II
Climate Change 2014: Impacts, Adaptation, and Vulnerability
http://ipcc-wg2.gov/AR5/report/final-drafts/
Other readings:
Other readings:
IPCC Report:
A changing climate creates pervasive risks but opportunities exist
for effective responses
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