The SRM approaches proposed to date can be divided into four broad categories: space, stratosphere, cloud, and surface based. Space-based proposals involve placing satellites with reflective surfaces in space. However, to counteract GHG-induced warming, 10 square miles of reflective surface would need to be put into orbit each day for as long as CO2 emissions continue to increase at current rates. The most widely discussed option for stratosphere-based SRM is the injection of sulfate aerosols, which would reflect some amount of incoming solar radiation back to space, offsetting some of the warming associated with GHGs. Another SRM option is to "whiten" clouds, or make them more reflective, by increasing the number of water droplets in the clouds. This could potentially be achieved over remote parts of the ocean by distributing a fine seawater spray in the air. Surface-based options include whitening roofs in the built environment, and planting more reflective crops. While these proposals merit incoming Solar Radïanon
Increase surface albedo
! GEOLOGICAL !
COASTAL \ CJl'
SEDIMENTS \ Enhance
1 1 \ upwelling top of atmosphere tmpopause
Enhance down welling
FIGURE 2.9 Various geoengineering options,including both solar radiation management and carbon dioxide removal. For further details see Figure 15.1. SOURCE: Lenton and Vaughn (2009).
further research, their efficacy and environmental consequences are not currently well understood.
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