Geoengineering refers to proposals to deliberately manipulate the Earth’s climate, usually to counteract the effects of Global warming. Advocates of the idea promote it based on the possibility that climate change may become so advanced that severe and dangerous effects are inevitable, or that positive feedback mechanisms may cause runaway climate change, even if emissions are substantially reduced. Most scientists, environmentalists, and engineers who advocate geoengineering see it as an additional measure required to stabilize the climate, not as a cheaper alternative to a low carbon economy.
Some geoengineering techniques seek to reduce greenhouse gases in the atmosphere directly. These include direct methods (e.g. carbon dioxide air capture) and indirect methods (e.g. ocean iron fertilization). Strategies for reducing greenhouse gases include creating biochar (anaerobic charcoal), and using biomass energy with carbon capture and storage.
Alternatively, solar radiation management techniques do not reduce greenhouse gas concentrations, and can only address the warming effects of carbon dioxide and other gases; they cannot address problems such as ocean acidification. Examples of these techniques include the production of stratospheric sulfur aerosols, cloud reflectivity enhancement, and space-based sunshades such as mirrors.
A degree of urgency in efforts to research and implement potential solutions is based on the possibility that tipping points in the Earth’s climate system are close at hand. In particular the Arctic shrinkage is causing accelerated regional warming due to positive feedback, as reflective Arctic sea ice gives way to open water, absorbing heat from the summer sun. Such positive feedback is characteristic of a tipping point, and can accelerate global warming and even cause abrupt climate change.
Bearing in mind the threats from climate change, it can be argued that attempting geoengineering represents a lesser risk than not pursuing such strategies. While the understanding of geoengineering techniques is limited, the risks of global warming are at least partially understood, and are severe. It has been argued that regardless of the economic, scientific and technical aspects, the difficulty of achieving concerted political action on climate change requires other approaches.
Many members of the scientific and technical communities fear that the effects of various geoengineering schemes are not well understood. Performance of the systems may become ineffective, unpredictable or unstable as a result of external events. The techniques themselves may cause significant foreseen or unforeseen harm. There may be unintended climatic consequences, such as changes to the hydrological cycle including droughts or floods, caused by the geoengineering techniques, but not predicted by models. Such effects may be cumulative or chaotic in nature, making prediction and control very difficult.
Geoengineering could in some cases create a clear division between winners and losers. Most of the proposed interventions are regional, such as modifications in the Arctic. Such interventions would compel those in the affected regions to tolerate the effects of geoengineering for the supposed benefit of the global climate.
Wikipedia on Geoengineering