It is an unpalatable truth that unless we can succeed in greatly reducing CO₂ emissions we are headed for a very uncomfortable and challenging climate future, and geoengineering will be the only option left to limit further temperature increases. Our research found that some geoengineering techniques could have serious unintended and detrimental effects on many people and ecosystems - yet we are still failing to take the only action that will prevent us from having to rely on them. Geoengineering and its consequences are the price we may have to pay for failure to act on climate change.

—Professor John Shepherd, chair of the Royal Society’s geoengineering study

The report assesses the two main kinds of geoengineering techniques: Carbon Dioxide Removal (CDR) and Solar Radiation Management (SRM). CDR techniques address the root of the problem—rising CO₂—and so have fewer uncertainties and risks, as they work to return the Earth to a more normal state. They are therefore considered preferable to SRM techniques, but none has yet been demonstrated to be effective at an affordable cost, with acceptable environmental impacts, and they only work to reduce temperatures over very long timescales.

SRM techniques act by reflecting the sun’s energy away from Earth—i.e., they lower temperatures rapidly, but do not affect CO₂ levels. They therefore fail to address the wider effects of rising CO₂, such as ocean acidification, and would need to be deployed for a very long time. Although they are relatively cheap to deploy, there are considerable uncertainties about their regional consequences, and they only reduce some, but not all, of the effects of climate change, while possibly creating other problems. The report concludes that SRM techniques could be useful if a threshold is reached where action to reduce temperatures must be taken rapidly, but that they are not an alternative to emissions reductions or CDR techniques.

None of the geoengineering technologies so far suggested is a magic bullet, and all have risks and uncertainties associated with them. It is essential that we strive to cut emissions now, but we must also face the very real possibility that we will fail. If “Plan B” is to be an option in the future, considerable research and development of the different methods, their environmental impacts and governance issues must be undertaken now. Used irresponsibly or without regard for possible side effects, geoengineering could have catastrophic consequences similar to those of climate change itself. We must ensure that a governance framework is in place to prevent this.

—Professor John Shepherd

Of the CDR techniques assessed, the following were considered to have most useful potential:

• CO₂ capture from ambient air – this would be the preferred method of geoengineering, as it effectively reverses the cause of climate change. At this stage no cost-effective methods have yet been demonstrated and much more research and development is needed.

• Enhanced weathering – this technique, which utilizes naturally occurring reactions of CO2 from the air with rocks and minerals, was identified as a prospective longer-term option. However more research is needed to find cost-effective methods and to understand the wider environmental implications.

• Land use and afforestation – the report found that land use management could and should play a small but significant role in reducing the growth of atmospheric CO₂ concentrations. However the scope for applying this technique would be limited by land use conflicts, and all the competing demands for land must be considered when assessing the potential for afforestation and reforestation.

Should temperatures rise to such a level where more rapid action needs to be taken, the following SRM techniques were considered to have most potential:

• Stratospheric aerosols – these were found to be feasible, and previous volcanic eruptions have effectively provided short-term preliminary case studies of the potential effectiveness of this method. The cost was assessed as likely to be relatively low and the timescale of action short. However, there are some serious questions over adverse effects, particularly depletion of stratospheric ozone.

• Space-based methods – these were considered to be a potential SRM technique for long-term use, if the major problems of implementation and maintenance could be solved. At present the techniques remain prohibitively expensive, complex and would be slow to implement.

• Cloud albedo approaches (eg. cloud ships) – the effects would be localized and the impacts on regional weather patterns and ocean currents are of considerable concern but are not well understood. The feasibility and effectiveness of the technique is uncertain. A great deal more research would be needed before this technique could be seriously considered.

The following techniques were considered to have lower potential:

• Biochar (CDR technique) – the report identified significant doubts relating to the potential scope, effectiveness and safety of this technique and recommended that substantial research would be required before it could be considered for eligibility for UN carbon credits.

• Ocean fertilization (CDR technique) – the report found that this technique had not been proved to be effective and had high potential for unintended and undesirable ecological side effects.

• Surface albedo approaches (SRM technique, including white roof methods, reflective crops and desert reflectors) – these were found to be ineffective, expensive and, in some cases, likely to have serious impacts on local and regional weather patterns.

The report makes a number of recommendations, including:

• Parties to the UNFCCC should make increased efforts towards mitigating and adapting to climate change, and in particular to agreeing to global emissions reductions of at least 50% on 1990 levels by 2050 and more thereafter. Nothing now known about geoengineering options gives any reason to diminish these efforts.

• Further 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. This should include appropriate observations, the development and use of climate models, and carefully planned and executed experiments.

• Evaluations of the geoengineering methods should take account of the major differences between the main two classes of methods—CDR and SRM.

• Geoengineering methods of both types should only be considered as part of a wider package of options for addressing climate change. CDR methods should be regarded as preferable to SRM methods as a way to augment continuing mitigation action in the long term. However, SRM methods may provide a potentially useful short-term backup to mitigation in case rapid reductions in global temperatures are needed.

• CDR methods that have been demonstrated to be safe, effective, sustainable and affordable should be deployed alongside conventional mitigation methods as soon as they can be made available.

• SRM methods should not be applied unless there is a need to rapidly limit or reduce global average temperatures. Because of the uncertainties over side-effects and sustainability they should only be applied for a limited time period, and if accompanied by aggressive programs of conventional mitigation and/or CDR so that their use may be discontinued in due course.

• To ensure that geoengineering methods can be adequately evaluated, and applied responsibly and effectively should the need arise, three priority programs of work are recommended:

  1. internationally coordinated research and technological development on the more promising methods identified in the report;
  2. international collaborative activities to further explore and evaluate the feasibility, benefits, environmental impacts, risks and opportunities presented by geoengineering, and the associated governance issues; and
  3. the development and implementation of governance frameworks to guide both research and development in the short term, and possible deployment in the longer term, including the initiation of stakeholder engagement and a public dialogue process.

• The governance challenges posed by geoengineering should be explored in more detail by an international body such as the UN Commission for Sustainable Development, and processes established for the development of policy mechanisms to resolve them.

• The Royal Society in collaboration with international science partners should develop a code of practice for geoengineering research and provide recommendations to the international scientific community for a voluntary research governance framework. This should provide guidance and transparency for geoengineering research, and apply to researchers working in the public, private and commercial sectors. It should include:

  1. Consideration of what types and scales of research require regulation including validation and monitoring;
  2. The establishment of a de minimis standard for regulation of research;
  3. Guidance on the evaluation of methods including relevant criteria, and life cycle analysis and carbon/climate accounting.

• Relevant international scientific organizations should coordinate an international programme of research on geoengineering methods with the aim of providing an adequate evidence base with which to assess their technical feasibility and risks, and reducing uncertainties within ten years.

• Relevant UK government departments should together fund a 10-year geoengineering research program at a level of the order of £10M per annum. This should actively contribute to the international program and be closely linked to climate research programs.

• The Royal Society, in collaboration with other appropriate bodies, should initiate a process of dialogue and engagement to explore public and civil society attitudes, concerns and uncertainties about geoengineering as a response to climate change.

Resources

• Geoengineering the climate: Science, governance and uncertainty (RS Policy document 10/09, September 2009)