Monday, March 31, 2014

IPCC’s WGII AR5 on Geoengineering (Ch. 19.5.4 added)

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 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

WGII AR5 Final Drafts (accepted).
Ch 20 — Climate-resilient pathways: adaptation, mitigation, and sustainable development


Climate Change 2014: Impacts, Adaptation, and Vulnerability

Other readings:

IPCC Report: 
A changing climate creates pervasive risks but opportunities exist
for effective responses
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