In order to slow down climate changes likely caused by the increase in human-generated greenhouse gases, some scientists and policymakers are exploring ways in which to cool the planet. A number of geoengineering strategies, or ways in which the environment might be manipulated to offset global warming, have emerged, though there is not yet an agreed upon definition of which methods should be categorized as geoengineering.
According to the Royal Society’s report on geoengineering the climate, released in 2009, there are two main approaches. One involves deflecting a small amount of the sun’s light and heat away from the planet to lower global temperatures; this could include the use of reflective aerosols or mirrors high in the atmosphere, or may require the deliberate formation of clouds. A second general method for cooling the planet involves removing carbon dioxide (CO2) from the atmosphere, either via sequestration or CO2 capture, or possibly through ocean iron fertilization to promote the growth of CO2-consuming algae.
These different geoengineering methods are at various levels of technological development, have very different costs/benefits, and are not expected to work equally efficiently. Currently, the only methods that are really considered ready or near-ready for deployment are forestation, and capture from fossil fuels combined with underground storage. For all the other methods there is much more uncertainty and/or much higher projected costs.