List of proposed geoengineering schemes

Solar Radiation Management
General proposals

Atmospheric projects
General proposals
 * Reflective aerosols or dust
 * Stratospheric sulfur aerosols
 * Reflective metal flakes
 * Reflective atmospheric dust
 * marine cloud brightening
 * Ocean sulfur cycle enhancement
 * Ocean mixing  This technique can give only 0.016W/m2 of globally-averaged negative forcing, which is essentially insignificant for geoengineering purposes.
 * Reflective balloons
 * Modified ship /aircraft exhaust composition

Cloud seeding
Cloud stimulation can be carried out using a variety of methods, such as burning sulfur in ships or power plants to form sulfate aerosol in order to stimulate additional low marine clouds to reflect sunlight. Liquid nitrogen can also be used, as can silver iodide "Earlier, Reck (1978) studied the effect of increases in cloud cover and, using a radiative-convective atmospheric model, found that a 4 to 5 percent increase in low-level cloud cover would be sufficient to offset the warming predicted from a doubling of preindustrial CO2. This value is in reasonable agreement with Randall et al. (1984), who estimated that a 4 percent increase was required in the amount of marine stratocumulus, which comprises the bulk of the low clouds on a global basis."

Cool roof


Painting pavements and roof materials in white or pale colours to reflect solar radiation, known as 'cool roof' technology, and encouraged by legislation in some areas (notably California). This is a benign technique, although limited in its ultimate effectiveness by the costrained surface area available for treatment. This technique can give between 0.01-0.19W/m2 of globally-averaged negative forcing, depending on whether cities or all settlements are so treated. This is generally insignificant when compared to the 3.7W/m2 of positive forcing from a doubling of CO2. However, in many cases it can be achieved at little or no cost by simply selecting different materials. Further, it can reduce the need for air conditioning, which causes CO2 emissions which worsen global warming. For this reason alone it is still demonstrably worth pursuing.

Reflective sheeting
Reflective plastic sheets covering 67,000 square miles of desert, to reflect the Sun’s energy. This technique can give globally-averaged 1.74W/m2 of negative forcing, which is insufficient to offset the 3.7W/m2 of positive forcing from a doubling of CO2, but is still a very significant contribution and is sufficient to offset the current level of warming (approx. 1.7W/m2). However, the effect would be strongly regional, and would not be ideal for controlling Arctic shrinkage, which is one of the most significant problems resulting from global warming.

Forestry

 * Tropical reforestation
 * Grassland modification
 * High-albedo crops.

Space projects

 * Space sunshade
 * Mining moon dust

Dispersive solutions
Several authors have proposed dispersing light before it reaches the Earth by putting a very large diffraction grating or lens in space, perhaps at the L1 point between the Earth and the Sun. This plan was proposed in 1989 by J. T. Early, and in 1997 by Edward Teller, Lowell Wood, and Roderick Hyde. In 2004, physicist and science fiction author Gregory Benford calculated that a concave rotating Fresnel lens 1000 kilometres across, yet only a few millimeters thick, floating in space at the L1 point, would reduce the solar energy reaching the Earth by approximately 0.5% to 1%. He estimated that this would cost around US$10 billion up front, and another $10 billion in supportive cost during its lifespan. Side-effects include that, if this lens were built and global warming were avoided, there would be less incentive to reduce greenhouse gases, and humans might continue to produce too much carbon dioxide until it caused some other environmental catastrophe, such as a chemical change in ocean water that could be disastrous to ocean life.


 * Diffraction grating or lens in space, (L1 point)

Biological processes

 * Ocean iron fertilization
 * Ocean urea fertilisation
 * Reforestation
 * Peat production
 * Ocean mixing

Physical processes

 * Biochar burial
 * Bio-energy with carbon storage
 * Burying biomass
 * Biomass ocean storage
 * Carbon capture and storage

Chemical techniques

 * Mineral carbonation / mineral sequestration.
 * Carbon negative cement manufacture
 * Oil shale ash

Chemical scrubbers

 * Carbon air capture
 * Ocean acid neutralisation
 * Ocean hydrochloric acid removal

Other greenhouse gas remediation

 * CFC laser photochemistry