News & Views item - september

News & Views item - September 2009

Royal Society Publishes Geoengineering the climate: Science, governance and uncertainty. (September 2, 2009)

Professor John Shepherd

In some 90 pages a committee of twelve, chaired by Professor John Shepherd, delivered its assessment of the options for fighting global warming with geoengineering.

In his forward to the report, Martin Rees, president of the Royal Society said:

The continuing rise in the atmospheric concentration of greenhouse gases, mainly caused by the burning of fossil fuels, is driving changes in the Earth’s climate. The long-term consequences will be exceedingly threatening, especially if nations continue ‘business as usual’ in the coming decades. Most nations now recognise the need to shift to a low-carbon economy, and nothing should divert us from the main priority of reducing global greenhouse gas emissions. But if such reductions achieve too little, too late, there will surely be pressure to consider a ‘plan B’—to seek ways to counteract the climatic effects of greenhouse gas emissions by ‘geoengineering’.

...In this report, the Royal Society aims to provide an authoritative and balanced assessment of the main geoengineering options. Far more detailed study would be needed before any method could even be seriously considered for deployment on the requisite international scale. Moreover, it is already clear than none offers a ‘silver bullet’, and that some options are far more problematic than others.

This report is therefore offered as a clarification of the scientific and technical aspects of geoengineering, and as a contribution to debates on climate policy.

The report points out that while geoengineering technologies were very likely to be technically possible, and some were considered to be potentially useful to augment the continuing efforts to mitigate climate change by reducing emissions, it identified major uncertainties regarding their effectiveness, costs and environmental impacts.

The committee's chairman, Professor Shepherd said: 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.

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.

The report assesses the two main kinds of geoengineering techniques – Carbon Dioxide Removal (CDR) and Solar Radiation Management (SRM). The former have fewer uncertainties and risks, and are considered preferable to Solar Radiation Management, but none has yet been demonstrated to be effective at an affordable cost with acceptable environmental impacts. Furthermore, they only work to reduce temperatures over very long timescales.

Solar Radiation Management techniques act by reflecting the sun’s energy away from Earth. They would lower temperatures rapidly, but not affect CO₂levels and therefore fail to address the wider effects of rising CO₂, such as ocean acidification. Although relatively cheap to deploy, there are considerable uncertainties about their regional consequences.

In summary the report considers the following three techniques to be the most promising:

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 utilises 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 Solar Radiation Management 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 localised 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 report considered the the following approaches "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 fertilisation (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.

Princeton University geoscientist Michael Oppenheimer, co-author (with Robert H. Boyle) of a 1990 book, Dead Heat: The Race Against The Greenhouse Effect and a long-time participant in the Intergovernmental Panel on Climate Change(IPCC), told ScienceInsider: "'It’s a pretty good report; it’s definitely constructive,' but he emphasizes the uncertainties even more than the report does. The report’s recommendation for further research will, he predicts, make it clear that the risk of geoengineering is too high, no matter how fierce the greenhouse turns out to be."