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Solar radiation management〔(【引用サイトリンク】title=A Framework to Prevent the Catastrophic Effects of Global Warming using Solar Radiation Management (Geo-Engineering) )〕 (SRM) projects (proposed and theoretical) are a type of climate engineering which seek to reflect sunlight and thus reduce global warming.〔(【引用サイトリンク】title=Metapress Hosting Services for Academic Publishers )〕 Proposed examples include the creation of stratospheric sulfate aerosols. Their principal advantages as an approach to climate engineering is the speed with which they can be deployed and become fully active, their potential low financial cost, and the reversibility of their direct climatic effects. Solar radiation management projects could, for example, be used as a temporary response while levels of greenhouse gases can be brought under control by greenhouse gas remediation techniques. They would not reduce greenhouse gas concentrations in the atmosphere, and thus do not address problems such as ocean acidification caused by excess carbon dioxide (CO2). By comparison, other climate engineering techniques based on greenhouse gas remediation, such as ocean iron fertilization, need to sequester the anthropogenic carbon excess before any reversal of global warming would occur. ==Background== Climate engineering projects have been proposed in order to reduce global warming. The effect of rising greenhouse gas concentrations in the atmosphere on global climate is a warming effect on the planet. By modifying the albedo of the Earth's surface, or by preventing sunlight reaching the Earth by using a solar shade, this warming effect can be cancelled out — although the cancellation is imperfect, with regional discrepancies remaining. Therefore, solar radiation management, or albedo modification, is considered to be a potential option for addressing climate change. As the National Academy of Sciences states in its 2015 report: “The two main options for responding to the risks of climate change involve mitigation—reducing and eventually eliminating human-caused emissions of CO2 and other greenhouse gases (GHGs)—and adaptation—reducing the vulnerability of human and natural systems to changes in climate. A third potentially viable option, currently under development but not yet widely deployed, is carbon dioxide removal (CDR) from the atmosphere accompanied by reliable sequestration. A fourth, more speculative family of approaches called albedo modification seeks to offset climate warming by greenhouse gases by increasing the amount of sunlight reflected back to space.” In this context, solar radiation management is widely viewed as a complement, not a substitute, to climate change mitigation and adaptation efforts. As The Royal Society concluded in its 2009 report: “Geoengineering methods are not a substitute for climate change mitigation, and should only be considered as part of a wider package of options for addressing climate change.” Or put another way: “The safest and most predictable method of moderating climate change is to take early and effective action to reduce emissions of greenhouse gases. No geoengineering method can provide an easy or readily acceptable alternative solution to the problem of climate change. Geoengineering methods could however potentially be useful in future to augment continuing efforts to mitigate climate change by reducing emissions, and so should be subject to more detailed research and analysis.”〔 The phenomenon of global dimming is widely known, and is not necessarily a climate engineering technique. It already occurs under current conditions, due to aerosols caused by pollution, or caused naturally as a result of volcanoes and major forest fires. However, its deliberate manipulation is a tool of the geoengineer. By intentionally changing the Earth's albedo, or reflectivity, scientists propose that we could reflect more heat back out into space, or intercept sunlight before it reaches the Earth through a literal shade built in space. A 2% albedo increase would roughly halve the effect of CO2 doubling. The National Academy of Sciences describes several of the potential benefits and risks of solar radiation management: “Modeling studies have shown that large amounts of cooling, equivalent in scale to the predicted warming due to doubling the CO2 concentration in the atmosphere, can be produced by the introduction of tens of millions of tons of aerosols into the stratosphere. …Preliminary modeling results suggest that albedo modification may be able to counter many of the damaging effects of high greenhouse gas concentrations on temperature and the hydrological cycle and reduce some impacts to sea ice. Models also strongly suggest that the benefits and risks will not be uniformly distributed around the globe.” The applicability of many techniques listed here has not been comprehensively tested. Even if the effects in computer simulation models or of small-scale interventions are known, there may be cumulative problems such as ozone depletion, which become apparent only from large scale experiments. Various small-scale experiments have been carried out on techniques such as cloud seeding, increasing the volume of stratospheric sulfate aerosols and implementing cool roof technology. As early as 1974, Russian expert Mikhail Budyko suggested that if global warming became a problem, we could cool down the planet by burning sulfur in the stratosphere, which would create a haze. Paul Crutzen suggested that this would cost 25 to 50 billion dollars per year.〔 (【引用サイトリンク】title=Aerosols: Effects of Haze and Cloud )〕〔 〕 A preliminary study by Edward Teller and others in 1997 presented the pros and cons of various relatively "low-tech" proposals to mitigate global warming through scattering/reflecting sunlight away from the Earth via insertion of various materials in the upper stratosphere, low earth orbit, and locations. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「solar radiation management」の詳細全文を読む スポンサード リンク
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