Geoengineering is a name for various proposals to deliberately manipulate the Earth’s climate to counteract the effects of global warming. The National Academy of Sciences has defined geoengineering as “options that would involve large-scale engineering of our environment in order to combat or counteract the effects of changes in atmospheric chemistry”:
The 2007 IPCC report concluded that geoengineering options, such as ocean fertilization to remove CO2 from the atmosphere, remained largely unproven. It was judged that reliable cost estimates for geoengineering had not yet been published:
However, there is still considerable interest in geoengineering, because many people deem it difficult to reduce carbon emissions in time to prevent dangerous global warming.
Enhanced weathering. Although relatively small-impact compared to some other schemes, still a huge project that would involve global scale modification of the planet’s feedback mechanisms.
Seeding the ocean with iron to increase phytoplankton populations. The idea is that iron availability is the bottleneck preventing increasing phytoplankton growth, which would take more carbon dioxide from the atmosphere. This plan appears to depend upon the phytoplankton sinking to the ocean bottom, sequestering carbon dixoide. What happens otherwise is unclear.
Cloud seeding. The idea is to introduce chemicals into the atmosphere and encourage cloud formation. The clouds will reflect solar radiation and reduce the rate of warming.
Sunlight reflection from the upper atmosphere. Placing small particles of certain kinds in the upper atmosphere is apparently a relatively inexpensive way of reflecting a significant fraction of incoming sunlight back into space. Early proposals suggested sulphate particles, but these may react chemically with ozone in an adverse way. An alternative proposal is suspension of tiny, harmless particles (sized at one-third of a micron) at about 80,000 feet up in the stratosphere.
A proposal by Ornstein et al is irrigated afforestation of deserts?. Some comments: the afforestation would also help to neutralize some of the past CO2 emissions. A weak point in the proposal is that desalination is energy intensive. Perhaps it could be combined with the DESERTEC project. To secure the carbon fixation the afforestation could be combined with the production of biochar.
There is an analysis by Tim Lenton of the University of East Anglia which concludes that only geoengineering that reflects sunlight are able to have a large enough effect over a sufficiently short time interval. (He also projects that most of these are mechanisms that need continually replenishing, and in the event of discontinuing an even more dramatic rise in temperatures could occur.)
John Baez interviewed Gregory Benford in Week 310 of This Week’s Finds, and Benford discussed a number of geoengineering ideas, including experiments and a proposal for an experiments. These are also discussed here:
Gregory Benford, Climate controls, Reason Magazine, November 1997.
Robert A. Metzger and Gregory Benford, Sequestering of atmospheric carbon through permanent disposal of crop residue, Climatic Change 49 (2001), 11-19.
Stuart E. Strand and Gregory Benford, Ocean sequestration of crop residue carbon: recycling fossil fuel carbon back to deep sediments, Environmental Science and Technology 43 (2009), 1000-1007.
This is another experiment that will be carried out:
Geoengineering faces ban is an excellent article in Nature News summarising some of the latest geoengineering developments.
American Geophysical Union (AGU), 2009: AGU position statement: Geoengineering the climate system see: http://www.agu.org/sci_pol/positions/geoengineering.shtml.
American Meteorological Society, 2009: Geoengineering the climate system: A policy statement of the American Meteorological Society, Bulletin of the American Meteorological Society 90(9), 1369–1370.
Kelsi Bracmort and Richard K. Lattanzio, Geoengineering: Governance and Technology Policy, Congressional Research Service, 2 January 2013.
During 22-26 March 2010 there was a conference at Asilomar that recommended a list of principles for geoengineering research. The conference was called the Asilomar International Conference on Climate Intervention, and its recommendations appear in this report:
Here are some of the references from this report:
P. J. Crutzen, Albedo enhancement by stratospheric sulfur injections: A contribution to resolve a policy dilemma?, Climatic Change 77 (2006), 211– 220, doi:10.1007/s10584-006-9101-y.
M. C. MacCracken, Beyond Mitigation: Potential Options for Counter-Balancing the Climatic and Environmental Consequences of the Rising Concentrations of Greenhouse Gases, Background Paper to the 2010 World Development Report, Policy Research Working Paper (RWP) 4938, The World Bank, Washington, DC, May 2009, 43 pp.
Rayner, S., C. Redgwell, J. Savulescu, N. Pidgeon and T. Kruger, 2009: Memorandum on draft principles for the conduct of geoengineering research, (the ‘Oxford Principles’) reproduced in House of Commons Science and Technology Committee, The Regulation of Geoengineering, Fifth Report of the Session 2009-10, Report together with formal minutes, oral and written evidence, HC 221, 18 March 2010.
Royal Society (prepared by J. Shepherd et al.), Geoengineering the Climate: Science, Governance and Uncertainty, Science Policy Centre of The Royal Society, London, 2009, 98 pp.
S. H. Schneider, Earth systems: Engineering and management, Nature 409 (2001), 417–421.
UNEP (prepared by C. P. McMullen and J. Jappour), Climate Change Science Compendium 2009, United Nations Environment Programme, Nairobi, Earthprint, 2009, 70 pp.
T. M. Wigley, A combined mitigation/geoengineering approach to climate stabilization, Science 314 (2006), 452–454. doi:10.1126/science.1131728.
Some articles that discuss potential drawbacks of geoengineering (see also the Nathan Urban’s blog comment)
Matthews and Caldeira, Transient climate–carbon simulations of planetary geoengineering, PNAS 104 (2007)
Trenberth and Dai, Effects of Mount Pinatubo volcanic eruption on the hydrological cycle as an analog of geoengineering Geophys. Res. Lett. 34 (2007)
Robock, 20 reasons why geoengineering may be a bad idea Bulletin of the Atomic Scientists (2008)
Ban-Weiss and Caldeira Geoengineering as an optimization problem Environ. Res. Lett. 5 (2010) 034009
Goes, Tuana and Keller The economics (or lack thereof) of aerosol geoengineering Climatic Change (2011)
Gardiner, Some Early Ethics of Geoengineering the Climate (in prep.)