From:
ipcc
Intergovernmental Panel on Climate Change
Working Group III – Mitigation of
Climate Change
Chapter 3
Social, Economic and Ethical
Concepts and Methods
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3.3.7
Geoengineering, ethics, and justice
Geoengineering
(also known as climate engineering [CE]), is large‐scale technical
intervention in the climate system that aims to cancel some of the effects of
GHG emissions (for more details see WGI 6.5 and WGIII 6.9). Geoengineering
represents a third kind of response to climate change, besides mitigation and
adaptation. Various options for geoengineering have been proposed, including
different types of solar radiation management (SRM) and carbon dioxide removal
(CDR). This section reviews the major moral arguments for and against
geoengineering technologies (for surveys see Robock, 2008; Corner and Pidgeon,
2010; Gardiner, 2010; Ott, 2010; Betz and Cacean, 2012; Preston, 2013). These
moral arguments do not apply equally to all proposed geoengineering methods and
have to be assessed on a case‐specific basis.7
Three lines
of argument support the view that geoengineering technologies might be
desirable to deploy at some point in the future. First, that humanity could end
up in a situation where deploying geoengineering, particularly SRM, appears as
a lesser evil than unmitigated climate change (Crutzen, 2006; Gardiner, 2010;
Keith et al., 2010; Svoboda, 2012a; Betz, 2012). Second, that geoengineering could
be a more cost‐effective response to climate change
than mitigation or adaptation (Barrett, 2008). Such efficiency arguments have
been criticized in the ethical literature for neglecting issues such as side‐effects, uncertainties, or fairness (Gardiner, 2010, 2011; Buck, 2012).
Third, that some aggressive climate stabilization targets cannot be achieved
through mitigation measures alone and thus must be complemented by either CDR
or SRM (Greene et al., 2010; Sandler, 2012).
Geoengineering
technologies face several distinct sets of objections. Some authors have
stressed the substantial uncertainties of large‐scale
deployment (for overviews of geoengineering risks see also Schneider (2008) and
Sardemann and Grunwald (2010)), while others have argued that some intended and
unintended effects of both CDR and SRM could be irreversible (Jamieson, 1996)
and that some current uncertainties are unresolvable (Bunzl, 2009).
Furthermore, it has been pointed out that geoengineering could make the
situation worse rather than better (Hegerl and Solomon, 2009; Fleming, 2010;
Hamilton, 2013) and that several technologies lack a viable exit option: SRM in
particular would have to be maintained as long as GHG concentrations remain
elevated (The Royal Society, 2009).
Arguments against geoengineering on the basis
of fairness and justice deal with the intra‐generational
and intergenerational distributional effects. SRM schemes could aggravate some
inequalities if, as expected, they modify regional precipitation and temperature
patterns with unequal social impacts (Bunzl, 2008; The Royal Society, 2009;
Svoboda et al., 2011; Preston, 2012). Furthermore, some CDR methods would
require large‐scale land transformations,
potentially
7 While the literature typically
associates some arguments with particular types of methods (e.g., the
termination problem with SRM), it is not clear that there are two groups of
moral arguments: those applicable to all SRM methods on the one side and those
applicable to all CDR methods on the other side. In other words, the moral
assessment hinges on aspects of geoengineering that are not connected to the
distinction between SRM and CDR.
________________________________________________________________________________
competing
with agricultural land‐use, with uncertain distributive
consequences. Other arguments against geoengineering deal with issues including
the geopolitics of SRM, such as international conflicts that may arise from the
ability to control the “global thermostat” (e.g., Schelling,
1996; Hulme, 2009), ethics (Hale and Grundy, 2009; Preston, 2011; Hale and
Dilling, 2011; Svoboda, 2012b; Hale, 2012b), and a critical assessment of
technology and modern ivilization in general (Fleming, 2010; Scott, 2012).
One of the
most prominent arguments against geoengineering suggests that geoengineering
research activities might hamper mitigation efforts (e.g., Jamieson, 1996;
Keith, 2000; Gardiner,2010), which presumes that geoengineering should not be
considered an acceptable substitute for mitigation. The central idea in that
research increases the prospect of geoengineering being regarded as a serious
alternative to emission reduction (for a discussion of different versions of
this argument see Hale, 2012a; Hourdequin, 2012). Other authors have argued,
based on historical evidence and analogies to other technologies, that
geoengineering research might make deployment inevitable (Jamieson, 1996; Bunzl,
2009), or that large‐scale field tests could amount to
full‐fledged deployment (Robock et al., 2010). It has also been argued that
geoengineering would constitute an unjust imposition of risks on future
generations, because the underlying problem would not be solved but only
counteracted with risky technologies (Gardiner, 2010; Ott, 2012; Smith, 2012).
The latter argument is particularly relevant to SRM technologies that would not
affect greenhouse gas concentrations, but it would also apply to some CDR
methods, as there may be issues of long‐term safety and
capacity of storage.
Arguments
in favour of research on geoengineering point out that research does not
necessarily prepare for future deployment, but can, on the contrary, uncover
major flaws in proposed schemes, avoid premature CE deployment, and eventually
foster mitigation efforts (e.g., Keith et al., 2010). Another justification for
Research and Development (R&D) is that it is required to help decision‐makers take informed decisions (Leisner and Müller‐Klieser, 2010).
Chapter 6
Assessing Transformation Pathways
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6.9 Carbon and radiation management and other geo-engineering options including environmental risks
Some
scientists have argued that it might be useful to consider, in addition to
mitigation and adaptation measures, various intentional interventions into the
climate system as part of a broader climate policy strategy (Keith, 2000;
Crutzen, 2006). Such technologies have often been grouped under the blanket
term ‘geoengineering’ or, alternatively, ‘climate engineering’(Keith, 2000;
Vaughan and Lenton, 2011). Calls for research into these technologies have
increased in recent years (Caldeira and Keith, 2010; Science and Technology
Committee, 2010), and several assessments have been conducted (Royal Society,
2009; Edenhofer et al., 2011; Ginzky et al., 2011; Rickels et al., 2011). Two
categories of geoengineering are generally distinguished. Removal of GHGs, in
particular carbon dioxide (termed ‘carbon dioxide removal’ or CDR, would reduce
atmospheric GHG concentrations. The boundary between some mitigation and some
CDR methods is not always clear (Boucher et al., 2011, 2013). ‘Solar radiation
management’ or SRM technologies aim to increase the reflection of sunlight to
cool the planet and do not fall within the usual definitions of mitigation and
adaptation. Within each of these categories, there is a wide range of
techniques that are addressed in more detail in Sections 6.5 and 7.7 of the WG
I report.
Many
geoengineering technologies are presently only hypothetical. Whether or not
they could actually contribute to the avoidance of future climate change
impacts is not clear (Blackstock et al., 2009; Royal Society, 2009). Beyond
open questions regarding environmental effects and technological feasibility,
questions have been raised about the socio-political dimensions of
geoengineering and its potential implications for climate politics (Barrett,
2008; Royal Society, 2009; Rickels et al., 2011). In the general discussion,
geoengineering has been framed in a number of ways (Nerlich and Jaspal, 2012;
Macnaghten and Szerszynski, 2013; Luokkanen et al., 2013; Scholte et al.,
2013), for instance, as a last resort in case of a climate emergency
(Blackstock et al., 2009; McCusker et al., 2012), or as a way to buy time for
implementing conventional mitigation (Wigley, 2006; Institution of Mechanical
Engineers, 2009; MacCracken, 2009). Most assessments agree that geoengineering
technologies should not be treated as a replacement for conventional mitigation
and adaptation due to the high costs involved for some techniques, particularly
most CDR methods, and the potential risks, or pervasive uncertainties involved
with nearly all techniques (Royal Society, 2009; Rickels et al., 2011). The
potential role of geoengineering as a viable component of climate policy is yet
to be determined, and it has been argued that geoengineering could become a
distraction from urgent mitigation and adaptation measures (Lin; Preston,
2013).
6.9.1
Carbon dioxide removal
6.9.1.1 Proposed carbon dioxide removal methods and
characteristics
Proposed
CDR methods involve removing CO2 from the atmosphere and storing the carbon in
land, ocean, or geological reservoirs. These methods vary greatly in their
estimated costs, risks to humans and the environment, potential scalability,
and notably in the depth of research about their potential and risks. Some
techniques that fall within the definition of CDR are also regarded as
mitigation measures such as afforestation and BECCS (see Glossary). The term
‘negative emissions technologies’ can be used as an alternative to CDR
(McGlashan et al., 2012; McLaren, 2012; Tavoni and Socolow, 2013).
The WG I
report (Section 6.5.1) provides an extensive but not exhaustive list of CDR
techniques (WG I Table 6.14). Here only techniques that feature more prominently
in the literature are covered. This includes (1) increased land carbon
sequestration by reforestation and afforestation, soil carbon management, or
biochar (see WG III Chapter 11); (2) increased ocean carbon sequestration by
ocean fertilization; (3) increased weathering through the application of ground
silicates to soils or the ocean; and (4) chemical or biological capture with
geological storage by BECCS or direct air capture (DAC). CDR techniques can be
categorized in alternative ways. For example, they can be categorized (1) as
industrial technologies versus ecosystem manipulation; (2) by the pathway for
carbon dioxide capture (e.g. McLaren, 2012; Caldeira et al., 2013); (3) by the
fate of the stored carbon (Stephens and Keith, 2008); and (4) by the scale of
implementation (Boucher et al., 2013). Removal of other GHGs, e.g., CH4 and
N2O, have also been proposed (Boucher and Folberth, 2010; de_Richter and
Caillol, 2011; Stolaroff et al., 2012).
All CDR
techniques have a similar slow impact on rates of warming as mitigation
measures (van Vuuren and Stehfest, 2013) (see WG I Section 6.5.1). An
atmospheric ‘rebound effect’ (see WG I Glossary) dictates that CDR requires
roughly twice as much CO2 removed from the atmosphere for any desired net reduction in atmospheric CO2
concentration, as some CO2 will be returned from the natural carbon sinks
(Lenton and Vaughan, 2009; Matthews, 2010). Permanence of the storage reservoir
is a key consideration for CDR efficacy. Permanent (larger than tens of thousands
of years) could be geological reservoirs while non‐permanent
reservoirs include oceans and land (the latter could, among others, be affected
by the magnitude of future climate change) (see WG I Section 6.5.1). Storage
capacity estimates suggest geological reservoirs could store several thousand
GtC; the oceans a few thousand GtC in the long term, and the land may have the
potential to store the equivalent to historical land‐use loss of 180
± 80 GtC (also see Table 6.15 of WG I)(Metz et al., 2005; House et al.,
2006; Orr, 2009; Matthews, 2010).
Ocean
fertilization field experiments show no consensus on the efficacy of iron
fertilization (Boyd et al., 2007; Smetacek et al., 2012). Modelling studies
estimate between 15 ppm and less than 100 ppm drawdown of CO2 from the
atmosphere over 100 years (Zeebe and Archer, 2005; Cao and Caldeira, 2010)
while simulations of mechanical upwelling suggest 0.9 Gt/yr (Oschlies et al.,
2010). The latter technique has not been field tested. There are a number of
possible risks including downstream decrease in productivity, expanded regions
of low‐oxygen concentration, and increased N2O emissions (See WG I Section
6.5.3.2) (low confidence). Given the uncertainties surrounding effectiveness
and impacts, this CDR technique is at a research phase with no active
commercial ventures. Furthermore, current international governance states that
marine geoengineering including ocean fertilization is to be regulated under
amendments to the London Convention/London Protocol on the Prevention of Marine
Pollution by Dumping of Wastes and Other Matter, only allowing legitimate
scientific research (Güssow et al., 2010; International Maritime Organization,
2013).
Enhanced
weathering on land using silicate minerals mined, crushed, transported, and
spread on soils has been estimated to have a potential capacity, in an
idealized study, of 1 GtC/yr (Köhler et al., 2010). Ocean‐based
weathering CDR methods include use of carbonate or silicate minerals processed
or added directly to the ocean (see WG I Section 6.5.2.3). All of these
measures involve a notable energy demand through mining, crushing, and
transporting bulk materials. Preliminary hypothetical cost estimates are in the
order of 23-66 USD/tCO2
(Rau and Caldeira, 1999; Rau et al., 2007) for land and 51-64 USD/tCO2 for ocean methods
(McLaren, 2012). The confidence level on the carbon cycle impacts of enhanced
weathering is low (WG I Section 6.5.3.3).
The use of
CCS technologies (Metz et al., 2005) with biomass energy also creates a carbon
sink (Azar et al., 2006; Gough and Upham, 2011). The BECCS is included in the
RCP 2.6 (van Vuuren et al., 2007, 2011b) and a wide range of scenarios reaching
similar and higher concentration goals. From a technical perspective, BECCS is
very similar to a combination of other techniques that are part of the
mitigation portfolio: the production of bio‐energy and CCS
for fossil fuels. Estimates of the global technical potential for BECCS vary
greatly ranging from 3 to more than 10 GtCO2/yr (Koornneef et al., 2012;
McLaren, 2012; van Vuuren et al., 2013), while initial cost estimates also vary
greatly from around 60 to 250 USD/tCO2 (McGlashan et al., 2012; McLaren, 2012).
Important limiting factors for BECCS include land availability, a sustainable
supply of biomass and storage capacity (Gough and Upham, 2011; McLaren, 2012).
There is also a potential issue of competition for biomass under bioenergy‐dependent mitigation pathways. Direct air capture uses a sorbent to
capture CO2 from the atmosphere and the long‐term storage of
the captured CO2 in geological reservoirs (GAO, 2011; McGlashan et al., 2012;
McLaren, 2012). There are a number of proposed capture methods including
adsorption of CO2 using amines in a solid form and the use of wet scrubbing
systems based on calcium or sodium cycling. Current research efforts focus on
capture methodologies (Keith et al., 2006; Baciocchi et al., 2006; Lackner,
2009; Eisenberger et al., 2009; Socolow et al., 2011) with storage technologies
assumed to be the same as CCS (Metz et al, 2005). A U.S. Government
Accountability Office (GAO) (2011) technology assessment concluded that all DAC
methods were currently immature. A review of initial hypothetical cost
estimates, summarizes 40-300
USD/tCO2 for supported amines and 165-600 USD/tCO2 for sodium or calcium scrubbers (McLaren, 2012) reflecting
an ongoing debate across very limited literature. Carbon dioxide captured
through CCS, BECCS, and DAC are all intended to use the same storage reservoirs
(in particular deep geologic reservoirs), potentially limiting their combined
use under a transition pathway.
6.9.1.2 Role of carbon dioxide removal in the
context of transformation pathways
Two of the
CDR techniques listed above, BECCS and afforestation, are already evaluated in
the current integrated models. For concentration goals on the order of 430-530 ppm CO2eq by 2100, BECCS forms
an essential component of the response strategy for climate change in the
majority of scenarios in the literature, particularly in the context of
concentration overshoot. As discussed in Section 6.2.2, BECCS offers additional
mitigation potential, but also an option to delay some of the drastic
mitigation action that would need to happen to reach lower GHG‐concentration goals by the second half of the century.
In
scenarios aiming at such low‐concentration levels, BECCS is
usually competitive with conventional mitigation technologies, but only after
these have been deployed at very large scale (see Azar et al., 2010; Tavoni and
Socolow, 2013). At same time, BECCS applications do not feature in less
ambitious mitigation pathways (van Vuuren et al., 2011a). Key implications of
the use of BECCS in transition pathways is that emission reduction decisions
are directly related to expected availability and deployment of BECCS in the
second half of the century and that scenarios might temporarily overshoot
temperature or concentration goals.
The vast
majority of scenarios in the literature show CO2 emissions of LUC become negative
in the second half of the century –even in the absence of mitigation
policy (see Section 6.3.2). This is a consequence of demographic trends and
assumptions on land‐use policy. Addition afforestation
as part of mitigation policy is included in a smaller set of models. In these
models, afforestation measures increase for lower‐concentration
categories, potentially leading to net uptake of carbon of around 10 GtCO2/yr.
There are
broader discussions in the literature regarding the technological challenges
and potential risks of large‐scale BECCS deployment. The
potential role of BECCS will be influenced by the sustainable supply of large‐scale biomass feedstock and feasibility of capture, transport, and long‐term underground storage of CO2 as well as the perceptions of these
issues. The use of BECCS faces large challenges in financing, and currently no
such plants have been built and tested at scale. Integrated modeling studies
have therefore explored the sensitivities regarding the availability of BECCS
in the technology portfolio by limiting bioenergy supply or CCS storage
(Section 6.3.6.3).
Only a few
papers have assessed the role of DAC in mitigation scenarios (e.g. Keith et
al., 2006; Keller et al., 2008; Pielke Jr, 2009; Nemet and Brandt, 2012; Chen
and Tavoni, 2013). These studies generally show that the contribution of DAC
hinges critically on the stringency of the concentration goal, the costs
relative to other mitigation technologies, time discounting and assumptions
about scalability. In these models, the influence of DAC on the mitigation
pathways is similar to that of BECCS (assuming similar costs). That is, it
leads to a delay in short‐term emission reduction in favour of
further reductions in the second half of the century. Other techniques are even
less mature and currently not evaluated in integrated models.
There are
some constraints to the use of CDR techniques as emphasized in the scenario
analysis. First of all, the potential for BECCS, afforestation, and DAC are
constrained on the basis of available land and/or safe geologic storage
potential for CO2. Both the potential for sustainable bio‐energy use
(including competition with other demands, e.g., food, fibre, and fuel
production) and the potential to store >100 GtC of CO2 per decade for many
decades are very uncertain (see previous section) and raise important societal
concerns. Finally, the large‐scale availability of CDR, by
shifting the mitigation burden in time, could also exacerbate inter‐generational impacts.
6.9.2
Solar radiation management
6.9.2.1 Proposed solar radiation management methods
and characteristics
SRM
geoengineering technologies aim to lower the Earth’s temperature by reducing
the amount of sunlight that is absorbed by the Earth’s surface, and thus
countering some of the GHG induced global warming. Most techniques work by
increasing the planetary albedo, thus reflecting a greater fraction of the
incoming sunlight back to space. A number of SRM methods have been proposed:
● Mirrors (or sunshades) placed
in a stable orbit between the Earth and Sun would directly reduce the
insolation the Earth receives (Early, 1989; Angel, 2006). Studies suggest that
such a technology is unlikely to be feasible within the next century (Angel,
2006).
● Stratospheric aerosol injection
would attempt to imitate the global cooling that large volcanic eruptions
produce (Budyko and Miller, 1974; Crutzen, 2006; Rasch et al., 2008). This
might be achieved by lofting sulphate aerosols (or other aerosol species) or their
precursors to the stratosphere to create a high‐altitude
reflective layer that would need to be continually replenished. Section 7.7.2.1
of WG I assessed that there is medium confidence that up to 4 Wm‐2 of forcing could be achieved with this approach.
● Cloud brightening might be
achieved by increasing the albedo of certain marine clouds through the
injection of cloud condensation nuclei, most likely sea salt, , producing an
effect like that seen when ship‐tracks of brighter clouds form
behind polluting ships (Latham, 1990; Latham et al.,2008, 2012). Section
7.7.2.2 of WG I assessed that too little was known about marine cloud
brightening to provide a definitive statement on its potential efficacy, but
noted that it might be sufficient to counter the radiative forcing that would
result from a doubling of CO2 levels.
● Various methods have been
proposed that could increase the albedo of the planetary surface, for example
in urban, crop, and desert regions (President’s Science
Advisory Committee. Environmental Pollution Panel, 1965; Gaskill, 2004; Hamwey,
2007; Ridgwell et al., 2009). These methods would likely only be possible on a
much smaller scale than those listed above. Section 7.7.2.3 of WG I discusses
these approaches.
This list
is non‐exhaustive and new proposals for SRM methods may be put forward in the
future. Another method that is discussed alongside SRM methods aims to increase
outgoing thermal radiation, reducing incoming solar radiation, through the
modification of cirrus clouds (Mitchell and Finnegan, 2009) (see WG I Section
7.7.2.4).
As SRM
geoengineering techniques only target the solar radiation budget of the Earth,
the effects of CO2 and other GHGs on the Earth System would remain, for
example, greater absorption and re-emission of thermal radiation by the
atmosphere (WG I Section 7.7), an enhanced CO2 physiological effect on plants
(WG I Section 6.5.4), and increased ocean acidification (Matthews et al.,
2009). Although SRM geoengineering could potentially reduce the global mean
surface air temperature, no SRM technique could fully return the climate to a
pre‐industrial or low‐CO2‐like state. One
reason for this is that global mean temperature and global mean hydrological
cycle intensity cannot be simultaneously returned to a pre‐industrial
state (Govindasamy and Caldeira, 2000; Robock et al., 2008; Schmidt et al.,
2012; Kravitz et al., 2013; MacMartin et al., 2013; Tilmes et al., 2013).
Section 7.7.3 of WG I details the current state of knowledge on the potential
climate consequences of SRM geoengineering. In brief, simulation studies
suggest that some SRM geoengineering techniques applied to a high‐CO2 climate could create climate conditions more like those of a low‐CO2 climate (Moreno‐Cruz et al., 2011; MacMartin et al.,
2013), but the annual mean, seasonality, and interannual variability of climate
would be modified compared to the pre‐industrial
climate (Govindasamy and Caldeira, 2000;
Lunt et al., 2008; Robock et al., 2008; Ban‐Weiss and
Caldeira, 2010; Moreno‐Cruz et al., 2011; Schmidt et al.,
2012; Kravitz et al., 2013; MacMartin et al., 2013). SRM geoengineering that
could reduce global mean temperatures would reduce thermosteric sea‐level rise and would likely also reduce glacier and ice‐sheet contributions to sea‐level rise (Irvine et al., 2009,
2012; Moore et al., 2010).
Model
simulations suggest that SRM would result in substantially altered global
hydrological conditions, with uncertain consequences for specific regional
responses such as precipitation and evaporation in monsoon regions (Bala et
al., 2008; Schmidt et al., 2012; Kravitz et al., 2013; Tilmes et al., 2013) .
In addition to the imperfect cancellation of GHG‐induced changes
in the climate by SRM, CO2 directly affects the opening of plant stomata, and
thus the rate of transpiration of plants and in turn the recycling of water
over continents, soil moisture, and surface hydrology (Bala et al., 2007; Betts
et al., 2007; Boucher et al., 2009; Spracklen et al., 2012).
Due to
these broadly altered conditions that would result from an implementation of
geoengineering, and based on experience from studies of the detection and
attribution of climate change, it may take many decades of observations to be
certain whether SRM is responsible for a particular regional trend in climate
(Stone et al., 2009; MacMynowski et al., 2011). These detection and attribution
problems also imply that field testing to identify some of the climate
consequences of SRM geoengineering would require deployment at a sizeable
fraction of full deployment for a period of many years or even decades (Robock
et al., 2010; MacMynowski et al., 2011).
It is
important to note that in addition to affecting the planet’s climate, many
SRM methods could have serious non‐climatic side‐effects. Any
stratospheric aerosol injection would affect stratospheric chemistry and has
the potential to affect stratospheric ozone levels. Tilmes et al. (2009) found
that sulphate aerosol geoengineering could delay the recovery of the ozone hole
by decades (WG I Section 7.7.2.1). Stratospheric aerosol geoengineering would
scatter light, modifying the optical properties of the atmosphere. This would
increase the diffuse‐to‐direct light
ratio, which would make the sky appear hazier (Kravitz et al., 2012), reduce
the efficacy of concentrated solar power facilities (Murphy, 2009), and
potentially increase the productivity of some plant species, and preferentially
those below the canopy layer, with unknown long‐term ecosystem
consequences (Mercado et al., 2009). The installations and infrastructure of
SRM geoengineering techniques may also have some negative effects that may be
particularly acute for techniques that are spatially extensive, such as desert
albedo geoengineering. SRM would have very little effect on ocean acidification
and the other direct effects of elevated CO2 concentrations that are likely to
pose significant risks (see WG I Section 6.5.4).
6.9.2.2 The relation of solar radiation management
to climate policy and transformation pathways
A key
determinant of the potential role, if any, of SRM in climate policy is that
some methods might act relatively quickly. For example, stratospheric aerosol
injection could be deployable within months to years, if and when the
technology is available, and the climate response to the resulting changes in
radiative forcing could occur on a timescale of a decade or less (e.g. Keith,
2000; Matthews and Caldeira, 2007; Royal Society, 2009; Swart and Marinova,
2010; Goes et al., 2011). Mitigating GHG emissions would affect global mean
temperatures only on a multi‐decadal to centennial time‐scale because of the inertia in the carbon cycle (van Vuuren and
Stehfest, 2013). Hence, it has been argued that SRM technologies could
potentially complement mitigation activities, for example, by countering global
GHG radiative forcing while mitigation activities are being implemented, or by
providing a back‐up strategy for a hypothetical
future situation where short‐term reductions in radiative forcing
may be desirable (Royal Society, 2009; Rickels et al., 2011). However, the
relatively fast and strong climate response expected from some SRM techniques
would also impose risks. The termination of SRM geoengineering forcing either
by policy choice or through some form of failure would result in a rapid rise
of global mean temperature and associated changes in climate, the magnitude of
which would depend on the degree of SRM forcing that was being exerted and the
rate at which the SRM forcing was withdrawn (Wigley, 2006; Matthews and
Caldeira, 2007; Goes et al., 2011; Irvine et al., 2012; Jones et al., 2013). It
has been suggested that this risk could be minimized if SRM geoengineering was
used moderately and combined with strong CDR geoengineering and mitigation
efforts (Ross and Matthews, 2009; Smith and Rasch, 2012). The potential of SRM
to significantly impact the climate on short time‐scales, at
potentially low cost, and the uncertainties and risks involved in this raise
important socio‐political questions in addition to
natural scientific and technological considerations in the section above.
The
economic analysis of the potential role of SRM as a climate change policy is an
area of active research and has, thus far, produced mixed and preliminary
results (see Klepper and Rickels, 2012). Estimates of the direct costs of
deploying various proposed SRM methods differ significantly. A few studies have
indicated that direct costs for some SRM methods might be considerably lower
than the costs of conventional mitigation, but all estimates are subject to
large uncertainties because of questions regarding efficacy and technical
feasibility (Coppock, 1992; Barrett, 2008; Blackstock et al., 2009; Robock et
al., 2009; Pierce et al., 2010; Klepper and Rickels, 2012; McClellan et al.,
2012).
However,
SRM techniques would carry uncertain risks, do not directly address some
impacts of anthropogenic GHG emissions, and raise a range of ethical questions
(see WG III Section 3.3.8) (Royal Society, 2009; Goes et al., 2011; Moreno‐Cruz and Keith, 2012; Tuana et al., 2012). While costs for the
implementation of a particular SRM method might potentially be low, a
comprehensive assessment would need to consider all intended and unintended
effects on ecosystems and societies and the corresponding uncertainties
(Rickels et al., 2011; Goes et al., 2011; Klepper and Rickels, 2012). Because
most proposed SRM methods would require constant replenishment and an increase
in their implementation intensity if emissions of GHGs continue, the result of
any assessment of climate policy costs is strongly dependent on assumptions
about the applicable discount rate, the dynamics of deployment, the
implementation of mitigation, and the likelihood of risks and side‐effects of SRM (see Bickel and Agrawal, 2011; Goes et al., 2011). While
it has been suggested that SRM technologies may buy time for emission
reductions (Rickels et al., 2011), they cannot substitute for emission
reductions in the long term because they do not address concentrations of GHGs
and would only partially and imperfectly compensate for their impacts.
The
acceptability of SRM as a climate policy in national and international socio‐political domains is uncertain. While international commitment is
required for effective mitigation, a concern about SRM is that direct costs
might be low enough to allow countries to unilaterally alter the global climate
(Bodansky, 1996; Schelling, 1996; Barrett, 2008). Barrett (2008) and Urpelainen
(2012) therefore argue that SRM technologies introduce structurally obverse
problems to the ‘free‐rider’ issue in climate change mitigation. Some studies suggest that
deployment of SRM hinges on interstate cooperation, due to the complexity of
the climate system and the unpredictability of outcomes if states do not
coordinate their actions (Horton, 2011). In this case, the political
feasibility of an SRM intervention would depend on the ability of state‐level actors to come to some form of agreement.
The
potential for interstate cooperation and conflict will likely depend on the
institutional context in which SRM is being discussed, as well as on the
relative importance given to climate change issues at the national and
international levels. Whether a broad international agreement is possible is a
highly contested subject (see Section 13.4.4) (EDF; The Royal Society; TWAS,
2012). Several researchers suggest that a UN‐based
institutional arrangement for decision making on SRM would be most effective
(Barrett, 2008; Virgoe, 2009; Zürn and Schäfer, 2013). So far there are no
legally binding international norms that explicitly address SRM, although
certain general rules and principles of international law are applicable (see
WG II, Chapter 13, p.37). States parties to the UN Convention on Biological
Diversity have adopted a non‐binding decision on geoengineering
that establishes criteria that could provide guidance for further development
of international regulation and governance (CBD Decision IX/16 C (ocean
fertilization) and Decision X/33(8)(w); see also LC/LP Resolutions LC‐LP.1(2008) and LC‐LP.2(2010), preamble).
Commentators
have identified the governance of SRM technologies as a significant political
and ethical challenge, especially in ensuring legitimate decision making,
monitoring, and control (Victor,2008; Virgoe, 2009; Bodansky, 2012). Even if
SRM would largely reduce the global temperature rise due to anthropogenic
climate change, as current modelling studies indicate, it would also imply a
spatial and temporal redistribution of risks. SRM thus introduces important
questions of intra‐ and intergenerational justice, both
distributive and procedural (see Wigley, 2006; Matthews and Caldeira, 2007;
Goes et al., 2011; Irvine et al., 2012; Tuana et al., 2012; Bellamy et al.,
2012; Preston, 2013).
Furthermore,
since the technologies would not remove the need for emission reductions, in
order to effectively ameliorate climate change over a longer term SRM
regulation would need to be based on a viable relation between mitigation and
SRM activities, and consider the respective and combined risks of increased GHG
concentrations and SRM interventions. The concern that the prospect of a viable
SRM technology may reduce efforts to mitigate and adapt has featured
prominently in discussions to date (Royal Society, 2009; Gardiner, 2011;
Preston, 2013).
Whether SRM
field research or even deployment would be socially and politically acceptable
is also dependent on the wider discursive context in which the topic is being
discussed. Bellamy et al. (2013) show that the success of mitigation policies
is likely to have an influence on stakeholder acceptability of SRM. While
current evidence is limited to few studies in a very narrow range of cultural
contexts, in a first review of early studies on perceptions of geoengineering,
Corner et al. (2012) find that participants of different studies tend to prefer
CDR over SRM and mitigation over geoengineering.
Considerations
that influence opinions are, amongst others, the perceived ‘naturalness’ of a
technology, its reversibility, and the capacity for responsible and transparent
governance (Corner et al., 2012). Furthermore, the way that the topic is framed
in the media and by experts plays an important role in influencing opinions on
SRM research or deployment (Luokkanen et al., 2013; Scholte et al., 2013). The
direction that future discussions may take is impossible to predict, since
deepened and highly differentiated information is rapidly becoming available
(Corner et al., 2012; Macnaghten and Szerszynski, 2013).
6.9.3
Summary
Despite the
assumption of some form of negative CO2 emissions in many scenarios, including
those leading to 2100 concentrations approaching 450 ppmv CO2eq, whether
proposed CDR or SRM geoengineering techniques can actually play a useful role
in transformation pathways is uncertain as the efficacy and risks of many
techniques are poorly understood at present. CDR techniques aim to reduce CO2
(or potentially other GHG) concentrations. A broad definition of CDR would
cover afforestation and BECCS, which are sometimes classified as mitigation
techniques, but also proposals that are very distinct in terms of technical
maturity, scientific understanding, and risks from mitigation such as ocean
iron fertilization. The former are often included in current integrated models
and scenarios and are, in terms of their impact on the climate, directly
comparable with techniques that are considered to be conventional mitigation,
notably fossil CCS and bio‐energy use. Both BECCS and
afforestation may play a key role in reaching low‐GHG
concentrations, but at a large scale have substantial land‐use demands
that may conflict with other mitigation strategies and societal needs such as
food production. Whether other CDR techniques would be able to supplement
mitigation at any significant scale in the future depends upon efficacy, cost,
and risks of these techniques, which at present are highly uncertain. The
properties of potential carbon storage reservoirs are also critically
important, as limits to reservoir capacity and longevity will constrain the
quantity and permanence of CO2 storage. Furthermore, some CDR techniques such
as ocean iron fertilization may pose transboundary risks. The impacts of CDR
would be relatively slow: climate effects would unfold over the course of
decades.
In contrast
to CDR, SRM would aim to cool the climate by shielding sunlight. These
techniques would not reduce elevated GHG concentrations, and thus not affect
other consequences of high‐GHG concentrations, such as ocean
acidification. Some SRM proposals could potentially cause a large cooling
within years, much quicker than mitigation or CDR, and a few studies suggest
that costs might be considerably lower than CDR for some SRM techniques. It has
thus been suggested that SRM could be used to quickly reduce global
temperatures or to limit temperature rise while mitigation activities are being
implemented. However, to avoid warming, SRM would need to be maintained as long
as GHG concentrations remain elevated. Modelling studies show that SRM may be
able to reduce global average temperatures but would not perfectly reverse all
climatic changes that occur due to elevated GHG concentrations, especially at
local to regional scales. For example, SRM is expected to weaken the global
hydrological cycle with consequences for regional precipitation patterns and
surface hydrology, and is expected to change the seasonality and variability of
climate. Because the potential climate impacts of any SRM intervention are
uncertain and evidence is very limited, it is too early to conclude how
effective SRM would be in reducing climate risks. SRM approaches may also carry
significant non‐climatic side‐effects. For
example, sulphate aerosol injection would modify stratospheric chemistry,
potentially reducing ozone levels, and would change the appearance of the sky. The
risks of SRM interventions and large‐scale
experiments, alongside any potential benefits, raise a number of ethical and
political questions that would require public engagement and international
cooperation to address adequately.
6.10
Gaps in knowledge and data
The
questions that motivate this chapter all address the broad characteristics of
possible long‐term transformation pathways toward
stabilization of GHG concentrations. The discussion has not focused on today’s
global or country‐specific technology strategies,
policy strategies, or other elements of a near‐term strategy.
It is therefore within this long‐term strategic context that gaps in
knowledge and data should be viewed. Throughout this chapter, a number of areas
of further development have been highlighted. Several areas would be most
valuable to further the development of information and insights regarding long‐term transformation pathways.
These
include the following: development of a broader set of socioeconomic and
technological storylines to support the development of future scenarios;
scenarios pursuing a wider set of climate goals including those related to
temperature change; more mitigation scenarios that include impacts from, and
adaptations to, a changing climate, including energy and land‐use systems critical for mitigation; expanded treatment of the benefits
and risks of CDR and SRM options; expanded treatment of co‐benefits and
risks of mitigation pathways; improvements in the treatment and understanding
of mitigation options and responses in end‐use sectors in
transformation pathways; and more sophisticated treatments of land use and land
use‐based mitigation options in mitigation scenarios. In addition, a major
weakness of the current integrated modelling suite is that regional definitions
are often not comparable across models. An important area of advancement would
be to develop some clearly defined regional definitions that can be met by most
or all models.
6.11
Frequently Asked Questions
FAQ 6.1. Is it
possible to bring climate change under control given where we are and what
options are available to us? What are the implications of delaying mitigation
or limits on technology options?
Many
commonly discussed concentration goals, including the goal of reaching 450 ppm
CO2eq by the end of the 21st century, are both physically and technologically
possible. However, meeting long‐term climate goals will require
large‐scale transformations in human societies, from the way that we produce
and consume energy to how we use the land surface, that are inconsistent with
both long‐term and short‐term trends. For example, to achieve
a 450 ppm CO2eq concentration by 2100, supplies of low‐carbon energy — energy from nuclear power, solar power, wind power, hydroelectric
power, bioenergy, and fossil resources with carbon dioxide capture and storage — might need to increase five‐fold or more
over the next 40 years. The possibility of meeting any concentration goal
therefore depends not just on the available technologies and current emissions
and concentrations, but also on the capacity of human societies to bear the
associated economic implications, accept the associated rapid and large‐scale deployment of technologies, develop the necessary institutions to
manage the transformation, and reconcile the transformation with other policy
priorities such as sustainable development. Improvements in the costs and
performance of mitigation technologies will ease the burden of this
transformation. In contrast, if the world’s countries cannot take on
sufficiently ambitious mitigation over the next 20 years, or obstacles impede
the deployment of important mitigation technologies at large scale, goals such
as 450 ppm CO2eq by 2100 may no longer be possible.
FAQ 6.2. What are the
most important technologies for mitigation? Is there a silver bullet
technology?
Limiting
CO2eq concentrations will require a portfolio of options, because no single
option is sufficient to reduce CO2eq concentrations and eventually eliminate
net CO2 emissions. Options include a range of energy supply technologies such
as nuclear power, solar energy, wind power, and hydroelectric power, as well as
bioenergy and fossil resources with carbon dioxide capture and storage. A range
of end‐use technologies will be needed to reduce energy consumption, and
therefore the need for low‐carbon energy, and to allow the use
of low‐carbon fuels in transportation, buildings, and industry. Halting
deforestation and encouraging an increase in forested land will help to halt or
reverse LUC CO2 emissions. Furthermore, there are opportunities to reduce non‐CO2 emissions from land use and industrial sources. Many of these
options must be deployed to some degree to stabilize CO2eq concentrations. A
portfolio approach can be tailored to local circumstances to take into account
other priorities such as those associated with sustainable development. At the
same time, if emissions reductions are too modest over the coming two decades,
it may no longer be possible to reach a goal of 450 ppm CO2eq by the end of the
century without large‐scale deployment of carbon dioxide
removal technologies. Thus, while no individual technology is sufficient,
carbon dioxide removal technologies could become necessary in such a scenario.
FAQ 6.3. How much
would it cost to bring climate change under control?
Aggregate
economic mitigation cost metrics are an important criterion for evaluating
transformation pathways and can indicate the level of difficulty associated
with particular pathways. However, the broader socio‐economic
implications of mitigation go beyond measures of aggregate economic costs, as
transformation pathways involve a range of tradeoffs that link to other policy
priorities. Global mitigation cost estimates vary widely due to methodological
differences along with differences in assumptions about future emissions
drivers, technologies, and policy conditions. Most scenario studies collected
for this assessment that are based on the idealized assumptions that all
countries of the world begin mitigation immediately, there is a single global
carbon price applied to well‐functioning markets, and key
technologies are available, find that meeting a 430-480 ppm CO2eq goal by
century’s end would entail a reduction in the amount global consumers spend of
1-4% in 2030, 2-6% in 2050, and 3-11% in 2100 relative to what would happen
without mitigation. To put these losses in context, studies assume that
consumption spending might grow from four‐ to over ten‐fold over the century without mitigation. Less ambitious goals are
associated with lower costs this century. Substantially higher and lower
estimates have been obtained by studies that consider interactions with pre‐existing distortions, non‐climate market failures, and
complementary policies. Studies explicitly exploring the implications of less‐idealized policy approaches and limited technology performance or
availability have consistently produced higher cost estimates. Delaying
mitigation would reduce near‐term costs; however studies indicate
that subsequent costs will rise much more rapidly to higher levels.
The complete chapters and report here:
Chapter 3
Social, Economic and Ethical
Concepts and Methods
Chapter 6
Assessing Transformation Pathways
Final Draft:
Climate
Change 2014: Mitigation of Climate Change
IPCC
Working Group III Contribution to AR5
