Climate engineering

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An oceanic phytoplankton bloom in the South Atlantic Ocean, off the coast of Argentina. The aim of ocean iron fertilization in theory is to increase such blooms by adding some iron, which would then draw carbon from the atmosphere and fix it on the seabed.

Climate engineering, also referred to as geoengineering, is the deliberate and large-scale intervention in the Earth’s climatic system with the aim of reducing global warming.[1][2][3] Climate engineering has two categories of technologies- carbon dioxide removal and solar radiation management. Carbon dioxide removal addresses a cause of climate change by removing one of the greenhouse gases from the atmosphere. Solar radiation management attempts to offset effects of greenhouse gases by causing the Earth to absorb less solar radiation.

Geoengineering has been proposed as a potential third option for tackling global warming, alongside mitigation and adaptation.[4] Scientists do not typically suggest geoengineering the climate as an alternative to emissions control, but rather an accompanying strategy.[5] Reviews of geoengineering techniques for climate control have emphasised that they are not substitutes for emission controls and have identified potentially stronger and weaker schemes.[6][7][8] The costs, benefits, and risks of many geoengineering approaches to climate change are not well understood.[9][10] However, a study from 2014 concluded that the most common climate engineering methods are either relatively ineffective or have potentially severe side effects and cannot be stopped without causing rapid climate change.[11]

There are no known large-scale climate engineering projects except one conducted outside the scientific mainstream by Russ George. Almost all research has consisted of computer modelling or laboratory tests, and attempts to move to real-world experimentation have proved controversial. Some limited tree planting[12] and cool roof[13] projects are already underway. Ocean iron fertilization has been given small-scale research trials.[14] Field research into sulfur aerosols has also started.[15]

Voices of caution against viewing geoengineered interventions as a simple solution to climate change are largely due to the risks and partially unknown side-effects of the technologies in question. Given the vastly insufficient action on emissions reductions in climate policy to date some have argued though that the risks of such interventions are to be seen in the context of risks of dangerous climate change.[16] As a rule of thumb it would appear that the scale of risks and costs of each climate engineering option appear to be somewhat inverse: The lower the costs, the greater the risks.[16][unbalanced opinion] Some have suggested that the concept of geoengineering the climate presents a moral hazard because it could reduce political and public pressure for emissions reduction.[17] Groups such as ETC Group[18] and individuals such as Raymond Pierrehumbert have called for a moratorium on deployment and out-of-doors testing of geoengineering techniques for climate control.[19][20]

Background[edit]

Several notable organizations have investigated geoengineering with a view to evaluating its potential, including the US Congress,[21] NASA,[22] the Royal Society,[23] the Institute of Mechanical Engineers,[24][25] and the UK Parliament.[26] The Asilomar International Conference on Climate Intervention Technologies was convened to identify and develop risk reduction guidelines for climate intervention experimentation.[27]

Major environmental organisations such as Friends of the Earth[28] and Greenpeace[29] have typically been reluctant to endorse solar radiation management, but are often more supportive of some carbon dioxide removal projects, such as afforestation and peatland restoration. Some authors have argued that any public support for geoengineering may weaken the fragile political consensus to reduce greenhouse gas emissions.[30]

Proposed strategies[edit]

Several geoengineering strategies have been proposed. IPCC documents detail several notable proposals.[31] These fall into two main categories: solar radiation management and carbon dioxide removal. However, other proposals exist.

The Geoengineering Climate: Technical Evaluation and Discussion of Impacts project of the National Academy of Sciences funded by United States agencies, including NOAA, NASA, and the CIA,[32] commenced in March 2013, is expected to issue a report in fall 2014.

"An ad hoc committee will conduct a technical evaluation of a limited number of proposed geoengineering techniques, including examples of both solar radiation management (SRM) and carbon dioxide removal (CDR) techniques, and comment generally on the potential impacts of deploying these technologies, including possible environmental, economic, and national security concerns. The study will:

  1. Evaluate what is currently known about the science of several (3-4) selected example techniques, including potential risks and consequences (both intended and unintended), such as impacts, or lack thereof, on ocean acidification,
  2. Describe what is known about the viability for implementation of the proposed techniques including technological and cost considerations,
  3. Briefly explain other geoengineering technologies that have been proposed (beyond the selected examples), and
  4. Identify future research needed to provide a credible scientific underpinning for future discussions.

The study will also discuss historical examples of related technologies (e.g., cloud seeding and other weather modification) for lessons that might be learned about societal reactions, examine what international agreements exist which may be relevant to the experimental testing or deployment of geoengineering technologies, and briefly explore potential societal and ethical considerations related to geoengineering. This study is intended to provide a careful, clear scientific foundation that informs ethical, legal, and political discussions surrounding geoengineering.

The project has support from the National Academy of Sciences, the U.S. intelligence community, the National Oceanic and Atmospheric Administration, and the National Aeronautics and Space Administration. The approximate start date for the project is March 2013; a report is expected be issued in fall 2014."[33]

Solar radiation management[edit]

Solar radiation management (SRM)[2][34] projects seek to reduce sunlight absorbed (ultra-violet, near infra-red and visible). This would be achieved by deflecting sunlight away from the Earth, or by increasing the reflectivity (albedo) of the atmosphere or the Earth's surface. These methods do not reduce greenhouse gas concentrations in the atmosphere, and thus do not seek to address problems such as the ocean acidification caused by CO2. Solar radiation management projects often have the advantage of speedy deployment and effect. While greenhouse gas remediation offers a more comprehensive possible solution to climate change, it does not give instantaneous results; for that, solar radiation management is required.[dubious ]

Solar radiation management methods[2] may include:

Carbon dioxide removal[edit]

Carbon dioxide removal projects seek to remove greenhouse gases from the atmosphere. Proposed methods include those that directly remove such gases from the atmosphere, as well as indirect methods that seek to use natural processes (e.g. tree planting). Many projects overlap with carbon capture and storage and carbon sequestration projects, and may not be considered to be geoengineering by all commentators. Techniques in this category include:

Significant reduction in ice volume in the Arctic Ocean in the range between 1979 and 2007 years

Detonation of a nuclear bomb on the lunar surface[edit]

It has been proposed that a nuclear missile could be fired into the lunar surface, thus creating a dust cloud between the Earth and the sun. This would deflect solar radiation and reduce warming, until the cloud eventually dissipated. Benefits of this strategy include that it is relatively cheap compared to other climate engineering projects, and that it does not involve specific ecosystem changes, and the resultant unknowns in effects on specific species on the planet Earth. Disadvantages include its uncertain level of effectiveness, ie that it might be 'too effective', and actually result in global cooling. The disadvantage quoted by many, that it would destabilise the moon's effect on tides and other earthly phenomena, is of course false, since the effect on the moon as a whole would be entirely negligible.

Justification[edit]

Tipping points and positive feedback[edit]

Climate change during the last 65 million years. The Paleocene–Eocene Thermal Maximum is labelled PETM.

It is argued that climate change may cross tipping points[37] where elements of the climate system may 'tip' from one stable state to another stable state, much like a glass tipping over. When the new state is reached, further warming may be caused by positive feedback effects,.[38] An example of a proposed causal chain leading to runaway global warming is the collapse of Arctic sea ice triggering subsequent release of methane.[39]

The precise identity of such "tipping points" is not clear, with scientists taking differing views on whether specific systems are capable of "tipping" and the point at which this "tipping" will occur.[40] An example of a previous tipping point is that which preceded the rapid warming leading up to the Paleocene–Eocene Thermal Maximum. Once a tipping point is crossed, cuts in anthropogenic greenhouse gas emissions will not be able to reverse the change. Conservation of resources and reduction of greenhouse emissions, used in conjunction with geoengineering, are therefore considered a viable option by some commentators.[41][42][43] Geoengineering offers the hope of temporarily reversing some aspects of climate change and allowing the natural climate to be substantially preserved whilst greenhouse gas emissions are brought under control and removed from the atmosphere by natural or artificial processes.

Costs[edit]

Some geoengineering techniques, such as cool roof techniques, can be achieved at little or no cost, and may even offer a financial payback.[44] IPCC (2007) concluded that reliable cost estimates for geoengineering options had not been published.[45] More recently, early research into costs of solar radiation management have been published.[46] This suggests that "well designed systems" might be available for costs in the order of a few hundred million dollars per year.[47] These are much lower than costs to achieve comprehensive reductions in CO2 emissions.[citation needed] Such costs would be within the budget of most nations, and even a handful of rich individuals.[48]

In their 2009 report Geoengineering the climate the Royal Society adjudged afforestation and stratospheric aerosols as the methods with the "highest affordability" (meaning lowest costs). Furthermore stratospheric aerosol injection, having the highest effectiveness and affordability, would be the nearest approximation to the "ideal method", with the (significant) disadvantage of high uncertainties considering safety and unwanted side effects. While afforestation scored highly for safety, it was found to be of limited effectiveness for treating climate change (see Table 5.1, Figure 5.1., pages 48–49)[2]

Ethics and responsibility[edit]

Climate engineering would represent a large-scale, intentional effort to modify the environment, which differ from inadvertent climate change through activities such as burning fossil fuels. Intentional climate change is viewed very differently from a moral standpoint.[49] This raises questions of whether we as humans have the right to change the climate, and under what conditions this right obtains. Furthermore, ethical arguments often confront larger considerations of worldview, including individual and social religious commitments. For many, religious beliefs are pivotal in defining the role of human beings in the wider world. Some religious communities might claim that humans have no responsibility in managing the climate, instead seeing such world systems as the exclusive domain of a Creator. In contrast, other religious communities might see the human role as one of "stewardship" or benevolent management of the world.[50] The question of ethics also relates to issues of policy decision-making. For example, the selection of a globally agreed target temperature is a significant problem in any geoengineering governance regime, as different countries or interest groups may seek different global temperatures.[51]

What most ethicists, policy-makers, and scientists agree on is this: Solar radiation management is an incomplete solution to global warming.[52] The possible option of geoengineering may reduce incentives to reduce emissions of greenhouse gases. It is argued that geoengineering could be used to 'buy time' before drastic climate change happens, allowing mitigation and adaptation measures more time to be implemented and work.[53] But the opposition points out that the resources spent on geoengineering could be used for mitigation and efforts to reduce emissions of greenhouse gases. Geoengineering also does not resolve other issues related to increasing levels of carbon dioxide.

Political viability[edit]

It has been argued that regardless of the economic, scientific and technical aspects, the difficulty of achieving concerted political action on climate change requires other approaches.[54] Those arguing political expediency say the difficulty of achieving meaningful emissions cuts[55] and the effective failure of the Kyoto Protocol demonstrate the practical difficulties of achieving carbon dioxide emissions reduction by the agreement of the international community.[56] However, others point to support for geoengineering proposals among think tanks with a history of climate change skepticism and opposition to emissions reductions as evidence that the prospect of geoengineering is itself already politicized and being promoted as part of an argument against the need for (and viability of) emissions reductions; that, rather than geoengineering being a solution to the difficulties of emissions reductions, the prospect of geoengineering is being used as part of an argument to stall emissions reductions in the first place.[57]

Geoenginering poses several challenges in the context of governance because of issues of power and jurisdiction.[47] Geoengineering as a climate change solution differs from other mitigation and adaptation strategies. Unlike a carbon trading system that would be focused on participation from multiple parties along with transparency, monitoring measures and compliance procedures; this is not necessarily required by geoengineering. Bengtsson[58] (2006) argues that "the artificial release of sulphate aerosols is a commitment of at least several hundred years". This highlights the importance for a political framework that is sustainable enough to contain a multilateral commitment over such a long period and yet is flexible as the techniques innovate through time. There are many controversies surrounding this topic and hence, geoengineering has been made into a very political issue. Most discussions and debates are not about which geoengineering technique is better than the other, or which one is more economically and socially feasible. Discussions are broadly on who will have control over the deployment of geoengineering and under what governance regime the deployment can be monitored and supervised. This is especially important due to the regional variability of the effects of many geoengineering techniques, benefiting some countries while damaging others. The challenge posed by geoengineering is not how to get countries to do it. It is to address the fundamental question of who should decide whether and how geoengineering should be attempted – a problem of governance.[59]

Risks and criticisms[edit]

Change in sea surface pH caused by anthropogenic CO2 between the 1700s and the 1990s. This ocean acidification will still be a major problem unless atmospheric CO2 is reduced.

Various criticisms have been made of geoengineering,[60] particularly Solar Radiaton Management (SRM) methods.[61] Decision making suffers from intransitivity of policy choice.[62] Some commentators appear fundamentally opposed. Groups such as ETC Group[18] and individuals such as Raymond Pierrehumbert have called for a moratorium on geoengineering techniques.[19][20]

Ineffectiveness[edit]

The effectiveness of the schemes proposed may fall short of predictions. In ocean iron fertilization, for example, the amount of carbon dioxide removed from the atmosphere may be much lower than predicted, as carbon taken up by plankton may be released back into the atmosphere from dead plankton, rather than being carried to the bottom of the sea and sequestered.[63]

Incomplete solution to CO2 emissions[edit]

Techniques that do not remove greenhouse gases from the atmosphere may control global warming, but do not reduce other effects from these gases, such as ocean acidification.[64] While not an argument against geoengineering per se, this is an argument against reliance on geoengineering to the exclusion of greenhouse gas reduction.

Control and predictability problems[edit]

The full effects of various geoengineering schemes are not well understood.[10] Matthews et al.[65] compared geoengineering to a number of previous environmental interventions and concluded that "Given our current level of understanding of the climate system, it is likely that the result of at least some geoengineering efforts would follow previous ecological examples where increased human intervention has led to an overall increase in negative environmental consequences."

Performance of the systems may become ineffective, unpredictable or unstable as a result of external events, such as volcanic eruptions, phytoplankton blooms, El Niño, solar flares, etc., potentially leading to profound and unpredictable disruption to the climate system.

It may be difficult to predict the effectiveness of projects,[66] with models of techniques giving widely varying results.[67] In the instances of systems which involve tipping points, this may result in irreversible effects. Climate modelling is far from an exact science even when applied to comparatively well-understood natural climate systems, and it is made more complex by the need to understand novel and unnatural processes which by definition lack relevant observation data.[68]

Side effects[edit]

The techniques themselves may cause significant foreseen or unforeseen harm. For example, the use of reflective balloons may result in significant litter,[69] which may be harmful to wildlife.

Ozone depletion is a risk of some geoengineering techniques, notably those involving sulfur delivery into the stratosphere.[70]

The active nature of geoengineering may in some cases create a clear division between winners and losers. Most of the proposed interventions are regional, such as albedo modification in the Arctic.[71]

There may be unintended climatic consequences, such as changes to the hydrological cycle[72] including droughts[73] or floods, caused by the geoengineering techniques, but possibly not predicted by the models used to plan them.[74] Such effects may be cumulative or chaotic in nature, making prediction and control very difficult.[75]

Not all side effects are negative, and an increase in agricultural productivity has been predicted by some studies.[76]

Unreliable systems[edit]

The performance of the interventions may be inconsistent due to mechanical failure, non-availability of consumables or funding problems.

The geoengineering techniques would, in many instances, be vulnerable to being switched off or deliberately destroyed. As examples, cloud making ships could be switched off or sunk and space mirrors could be tilted to make them useless. Anyone capable of exerting such power may seek to abuse it for commercial gain, military advantage or simple terrorism.

Termination shock[edit]

If solar radiation management were to abruptly stop, the climate would rapidly warm.[77] This would cause a sudden rise in global temperatures towards levels which would have existed without the use of the geoengineering technique. The rapid rise in temperature may lead to more severe consequences than a gradual rise of the same magnitude.[77]

Weaponisation[edit]

In 1976, 85 countries signed the U.N. Convention on the Prohibition of Military or Any Other Hostile Use of Environmental Modification Techniques.[47] The Environmental Modification Convention generally prohibits weaponising geoengineering techniques. However, this does not eliminate the risk. Geoengineering techniques may serve as weapons of mass destruction, creating droughts or famines designed to destroy or disable an enemy.[78] They could also be used simply to make battlefield conditions more favourable to one side or the other in a war.[79] For example, laser-guided weapons are confounded by clouds, and thus switching off cloud machines would favour forces using such weapons, and switching them on would favour ground forces defending against them.[80]

Whilst laws or treaties may prevent the manipulation of the climate as a weapon of war,[81] it could be argued that geoengineering is itself a manipulation, and thus destroying or disabling the geoengineering structures is not prohibited. A new legal framework may be necessary in the event that large-scale geoengineering becomes established.[original research?]

Carnegie's Ken Caldeira said, "It will make it harder to achieve broad consensus on developing and governing these technologies if there is suspicion that gaining military advantage is an underlying motivation for its development..."[82]

Effect on sunlight, sky and clouds[edit]

Managing solar radiation using aerosols or cloud cover would change the ratio between direct and indirect solar radiation. This may affect plant life[83] and solar energy.[84] There will be a significant effect on the appearance of the sky from aerosol projects, notably a hazing of blue skies and a change in the appearance of sunsets.[85] Aerosols may affect the formation of clouds, especially cirrus clouds.[86]

Moral hazard[edit]

The existence of such techniques may reduce the political and social impetus to reduce carbon emissions.[87] However, this issue has been researched in an in-depth study by Ipsos MORI for NERC,[88] which does not support the Moral Hazard argument. Other modelling work suggests that the threat of geoengineering by a rogue state may in fact increase the likelihood of emissions reduction.[89] The issue of moral hazard means that many environmental groups and campaigners are reluctant to advocate geoengineering for fear of reducing the imperative to cut greenhouse gas emissions.[90]

Other criticism comes from those who see geoengineering projects as reacting to the symptoms of global warming rather than addressing the real causes of climate change. Because geoengineering is a form of controlling the risks associated with global warming, it leads to a moral hazard problem. The problem is that knowledge that geoengineering is possible could lead to climate impacts seeming less fearsome, which could in turn lead to an even weaker commitment to reducing greenhouse gas emissions.[91]

Governance[edit]

Geoengineering opens up various political and economic issues. David Keith argues that the cost of geoengineering the Earth is within the realm of small countries, large corporations, or even very wealthy individuals.[92] Steve Rayner agrees that not all geoengineering possibilities are expensive, and that some, such as ocean iron fertilisation, are within the reach of very wealthy individuals, calling them a "Greenfinger" (after the fictional Goldfinger).[93][94] David Victor suggests that geoengineering is within the reach of any individual who has a small fraction of the bank account of Bill Gates, who takes it upon him or her self to be the "self-appointed protector of the planet".[95] However, it has been argued that a rogue state threatening geoengineering may strengthen action on mitigation.[89]

This may seem to eliminates any control over who gets to decide when to cool the Earth and how this should be done.[92] The resulting power would be enormous, and could not necessarily be readily controlled by legal, political or regulatory systems.[93] The legal and regulatory systems may face a significant challenge in effectively regulating the use of these technologies in a manner that allows for an acceptable result for society. There are however significant incentives for states to cooperate in choosing a specific geoengineering policy, which make unilateral deployment a rather unlikely event.[96]

A small number carbon offsetting firms have in the past attempted to set up unregulated and unsupervised geoengineering projects. In the long-run such firms may aim to sell carbon credits to individuals, firms or countries.

Geoengineering has the potential to cause significant environmental damage, and could even end up releasing further greenhouse gases into the atmosphere.[97] Opposition to some early schemes has been intense, with respected environmental groups campaigning against them.[98] Some researchers have suggested that building a global agreement on geoengineering deployment will be very difficult, and instead power blocs are likely to emerge.[99]

There is presently a lack of a universally agreed framework for the regulation of either geoengineering activity or research. The London Convention addresses some aspects of the law in relation to biomass ocean storage and ocean fertilization. Scientists at the Oxford Martin School at Oxford University have proposed a set of voluntary principles, which may guide geoengineering research. The short version of the 'Oxford Principles'[100] is:

  • Principle 1: Geoengineering to be regulated as a public good.
  • Principle 2: Public participation in geoengineering decision-making
  • Principle 3: Disclosure of geoengineering research and open publication of results
  • Principle 4: Independent assessment of impacts
  • Principle 5: Governance before deployment

These principles have been endorsed by the House of Commons of the United Kingdom Science and Technology Select Committee on “The Regulation of Geoengineering”,[101] and have been referred to by authors discussing the issue of governance.[102]

The Asilomar conference was replicated to deal with the issue of geoengineering governance,[102] and covered in a TV documentary, broadcast in Canada.

Implementation issues[edit]

There is no general consensus that geoengineering is safe, appropriate or effective, for the reasons listed above. Other environmentalists see calls for geoengineering as part of an explicit strategy to delay emissions reductions on the part of those with connections to coal and oil industries.[103][improper synthesis?]

All proposed geoengineering techniques require implementation on a relatively large scale, in order to make a significant difference to the Earth's climate. The least costly schemes are budgeted at a cost of millions,[104] with many more complex schemes such as space sunshade costing far more.

Many techniques, again such as space sunshade, require a complex technical development process before they are ready to be implemented. There is no clear institutional mechanism for handling this research and development process. As a result, many promising techniques do not have the engineering development or experimental evidence to determine their feasibility or efficacy at present.

Once a technique has been developed and tested, its implementation is still likely to be difficult. Climate change is by nature a global problem, and therefore no one institution, company or government is responsible for it. The substantial costs of most geoengineering techniques therefore cannot currently be apportioned. Roll-out of such technologies is therefore likely to be delayed until these issues can be resolved. A notable exception is the use of small albedo manipulation projects, known as cool roof, in which the colour of roofing or paving surfaces can be manipulated to reflect solar radiation back into space. These can be, and are, implemented by individuals, companies and governments without controversy.[105]

Due to the radical changes caused by geoengineering interventions, legal issues are also an impediment to implementation. The changes resulting from geoengineering necessarily benefit some people and disadvantage others. There may therefore be legal challenges to the implementation of geoengineering techniques by those adversely affected by them.[106]

Evaluation of geoengineering[edit]

Most of what is known about the suggested techniques is based on laboratory experiments, observations of natural phenomena and on computer modelling techniques. Some geoengineering schemes employ methods that have analogues in natural phenomena such as stratospheric sulfur aerosols and cloud condensation nuclei. As such, studies about the efficacy of these schemes can draw on information already available from other research, such as that following the 1991 eruption of Mount Pinatubo. However, comparative evaluation of the relative merits of each technology is complicated, especially given modelling uncertainties and the early stage of engineering development of many geoengineering schemes.[107]

Reports into geoengineering have also been published in the United Kingdom by the Institution of Mechanical Engineers[7] and the Royal Society.[8] The IMechE report examined a small subset of proposed schemes (air capture, urban albedo and algal-based CO2 capture schemes), and its main conclusions were that geoengineering should be researched and trialled at the small scale alongside a wider decarbonisation of the economy.[7]

The Royal Society review examined a wide range of geoengineering schemes and evaluated them in terms of effectiveness, affordability, timeliness and safety (assigning qualitative estimates in each assessment). Similarly to Lenton and Vaughan,[6] the report divided schemes into "carbon dioxide removal" (CDR) and "solar radiation management" (SRM) approaches that respectively address longwave and shortwave radiation. The key recommendations of the report were that "Parties to the UNFCCC should make increased efforts towards mitigating and adapting to climate change, and in particular to agreeing to global emissions reductions", and that "[nothing] now known about geoengineering options gives any reason to diminish these efforts".[8] Nonetheless, the report also recommended that "research and development of geoengineering options should be undertaken to investigate whether low risk methods can be made available if it becomes necessary to reduce the rate of warming this century".[8]

In a 2009 review study, Lenton and Vaughan evaluated a range of geoengineering schemes from those that sequester CO2 from the atmosphere and decrease longwave radiation trapping, to those that decrease the Earth's receipt of shortwave radiation.[6] In order to permit a comparison of disparate techniques, they used a common evaluation for each scheme based on its effect on net radiative forcing. As such, the review examined the scientific plausibility of schemes rather than the practical considerations such as engineering feasibility or economic cost. Lenton and Vaughan found that "[air] capture and storage shows the greatest potential, combined with afforestation, reforestation and bio-char production", and noted that "other suggestions that have received considerable media attention, in particular "ocean pipes" appear to be ineffective".[6] They concluded that "[climate] geoengineering is best considered as a potential complement to the mitigation of CO2 emissions, rather than as an alternative to it".[6]

In October 2011, a Bipartisan Policy Center panel issued a report urging immediate researching and testing in case "the climate system reaches a 'tipping point' and swift remedial action is required".[108] The National Academy of Sciences is running 21-month project which will study how humans might influence weather patterns, assess dangers and investigate possible national security implications of geoengineering attempts. The project will be funded by the CIA, the National Oceanic and Atmospheric Administration, and NASA.[109]

Intergovernmental Panel on Climate Change[edit]

The Intergovernmental Panel on Climate Change (IPCC) has assessed the scientific literature on climate engineering (referred to as "geoengineering" in its reports). The IPCC's Fourth Assessment Report was published in 2007. It states:[45]

Geo-engineering options, such as ocean fertilization to remove CO2 directly from the atmosphere, or blocking sunlight by bringing material into the upper atmosphere, remain largely speculative and unproven, and with the risk of unknown side-effects. Reliable cost estimates for these options have not been published

Working Group I's contribution to the IPCC's Fifth Assessment Report was published in 2013. It states:[110]

Models suggest that if SRM methods were realizable they would be effective in countering increasing temperatures, and would be less, but still, effective in countering some other climate changes. SRM would not counter all effects of climate change, and all proposed geoengineering methods also carry risks and side effects. Additional consequences cannot yet be anticipated as the level of scientific understanding about both SRM and CDR is low. There are also many (political, ethical, and practical) issues involving geoengineering that are beyond the scope of this report.

See also[edit]

References[edit]

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