Geoengineering

The concept of geoengineering (or climate engineering, climate remediation, and climate intervention) refers to "the deliberate large-scale intervention in the Earth’s climate system, in order to moderate global warming". The discipline divides broadly into two categories, as described by the Royal Society: "Carbon dioxide removal techniques address the root cause of climate change by removing greenhouse gases from the atmosphere. Solar radiation management techniques attempt to offset effects of increased greenhouse gas concentrations by causing the Earth to absorb less solar radiation." The Intergovernmental Panel on Climate Change concluded in 2007 that geoengineering options remained largely unproven. It was judged that reliable cost estimates for geoengineering had not yet been published.

Geoengineering has been proposed as a potential third option for tackling global warming, alongside mitigation and adaptation. Scientists do not typically suggest geoengineering as an alternative to emissions control, but rather an accompanying strategy. Reviews of geoengineering techniques have emphasised that they are not substitutes for emission controls and have identified potentially stronger and weaker schemes. However, such is the lifetime of some greenhouse gases in the atmosphere, most notably carbon dioxide, that geoengineering represents the only currently known method for reducing Earth's temperature in the short term (years to decades).

To date, no large-scale geoengineering projects have been acknowledged publicly, and almost all research has consisted of computer modelling or laboratory tests. Some limited tree planting and cool roof projects are already underway, and ocean iron fertilization is at a beginning stage of research, with small-scale research trials and global modelling having been completed. Field research into sulfur aerosols has also started.

Various criticisms have been made of geoengineering and some commentators appear fundamentally opposed. Some have suggested that the concept of geoengineering presents a moral hazard because it could reduce the political and popular pressure for emissions reduction. Groups such as ETC Group and individuals such as Raymond Pierrehumbert have called for a moratorium on deployment and out-of-doors testing of geoengineering techniques. The effectiveness of the schemes proposed may fall short of predictions. The full effects of various geoengineering schemes are not well understood.