Geoengineering

The modern concept of geoengineering (or climate engineering) is usually taken to mean proposals to deliberately manipulate the Earth's climate to counteract the effects of global warming from greenhouse gas emissions. The National Academy of Sciences defines geoengineering as "options that would involve large-scale engineering of our environment in order to combat or counteract the effects of changes in atmospheric chemistry." The Intergovernmental Panel on Climate Change (IPCC) (2007) concluded that geoengineering options, such as ocean fertilization to remove CO2 from the atmosphere, remained largely unproven.

Techniques and research
Some geoengineering techniques are based on carbon sequestration. These include direct methods, such as capturing carbon and storing it underground, and indirect methods, such as fertilizing the ocean with iron or nitrogen in the hope that the resulting algal bloom will provide long-term storage of carbon dioxide. Alternatively, solar radiation management techniques are designed to block absorption of the sun's rays, and do not reduce greenhouse gas concentrations. Examples of proposed solar radiation management techniques include the production of stratospheric sulfur aerosols, space mirrors, and cloud reflectivity enhancement, all designed to reflect sunlight.

Ocean iron fertilization is at an advanced stage of research, with small-scale research trials and global modelling having been completed. Field research into sulfur aerosols has also started, with the first small-scale test carried out in Russia in early 2009.

Side effects
Most techniques have at least some side effects. Two decades of scientific study have shown that ocean fertilisation offers a low probability of lasting benefits and a high probability of harm, while possible negative side effects from sulfur aerosols include drought, ozone depletion, whitening of the sky, decreased solar light, and uneven and unknown effects on clouds and ecosystems, including the potential of uncontrollable cooling.

2010 study: Geoengineering wont address sea level rise
A 2010 study published in the journal Proceedings of the National Academy of Sciences (PNAS) found that even the most extreme geoengineering approaches will not stop sea levels from rising due to climate change, and that as many as 150 million people could be affected as ocean levels increases by 30cm to 70cm by the end of this century, which could result in flooding of low-lying coastal areas, including some of the world's largest cities.

Scientists led by John Moore from Beijing Normal University, China, write that to combat global warming, people need to concentrate on sharply curbing greenhouse gas emissions and not rely too much on proposed geoengineering methods. Another researcher, Dr. Jevrejeva, and her colleagues examined two geoengineering schemes with five different scenarios: 1.) limiting incoming solar radiation through the injection of SO2 (sulphur dioxide) aerosols into the stratosphere; 2.) giant mirrors launched into orbit; 3.) modifying the carbon cycle by planting more trees (afforestation); 4.) converting organic material into charcoal (biochar); and 5.) using renewable energy from materials derived from biological sources (bioenergy). Using computer models, the team found that, if taken individually, even the most extreme of these methods would result in severe sea-level rise.

Reactions
Some commentators have suggested that consideration of geoengineering presents a moral hazard because it threatens to reduce the political and popular pressure for emissions reduction. Typically, the scientists and engineers proposing geoengineering strategies do not suggest that they are 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.

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