'Block the sun, control global warming'

1: Research to block the sun to cool the earth and limit global warming is of interest to several researchers.
The field is currently experiencing a surge of interest as it has now become broadly accepted that global warming is both real and dangerous. A degree of urgency in efforts to research and implement potential solutions is based on the historic failure to control emissions, and the possibility that tipping points in the Earth's climate system are close at hand.[17] In particular the Arctic shrinkage is causing accelerated regional warming. Rapid action with geoengineering may be necessary. Other tipping points might be avoided by reducing the impact of global warming in order to stifle positive feedback and prevent the resulting accelerated climate change.
The study of geoengineering is a notably complex discipline, as it requires the collation of knowledge in:
• scientific disciplines including atmospheric chemistry ecology, meteorology plant biology
• engineering disciplines including aeronautical engineering, naval architecture ballistics
• management and control disciplines such as risk management operational research
Several notable organisations have recently or are soon to, investigate geoengineering with a view to evaluating its potential. Notably NASA the Royal Society the Institute of Mechanical Engineers and the UK Parliament, have all held inquiries or contests aimed at discovering and evaluating current knowledge of the subject.
The major environmental organisations such as Friends of the Earth and Greenpeace have typically been reluctant to endorse geoengineering. Some have argued that any public support for geoengineering may weaken the fragile political consensus to reduce greenhouse gas emissions.
Solar radiation management (SRM) projects seek to reduce the amount of sunlight hitting the Earth and thus counteract global warming. They do not reduce greenhouse gas concentrations in the atmosphere and thus do not address problems such as ocean acidification caused by these gases. The phenomenon of global dimming is widely-known, and is not necessarily a geoengineering technique, occurring naturally as a result of volcanoes and major forest fires. However its deliberate manipulation is a tool of the geoengineer.
Solar radiation management projects often have the advantage of speed. Whilst Greenhouse gas remediation offers a comprehensive possible solution to climate change, it does not give instant results for that solar radiation management is required.
Techniques that fall into this category include:
• Creating stratospheric sulfur aerosols
• Cool roof – using pale-coloured roofing and paving materials
• Cloud reflectivity enhancement – using fine sea water spray to whiten clouds and increase cloud reflectivity.
• Space sunshade - obstructing solar radiation with space-based mirrors or other structures
• Cloud seeding of cirrus clouds, possibly using airliners.
Few field experiments in geoengineering have been carried out. Most of what is known about the suggested techniques is based on small-scale trials and from simulations of global climate models and other computer modelling techniques. Some geoengineering schemes employ methods that have analogues in natural phenomena such as stratospheric sulfur aerosols and cloud condensation nuclei. As such, studies about the efficacy of these schemes can draw on information already available from other research, such as that following the 1991 eruption of Mount Pinatubo. However, comparative evaluation of the relative merits of each technology is complicated, especially given modelling uncertainties and the early stage of engineering development of many geoengineering schemes.
In a 2009 review study, Lenton and Vaughan evaluated a range of geoengineering schemes from those that sequester CO2 from the atmosphere and decrease longwave radiation trapping to those that decrease the Earth's receipt of shortwave radiation. In order to permit a comparison of disparate techniques, they used a common evaluation for each scheme based on its effect on net radiative forcing. As such the review examined the scientific plausibility of schemes rather than the practical considerations such as engineering feasibility or economic cost. Lenton and Vaughan found that "[air] capture and storage shows the greatest potential, combined with afforestation, reforestation and bio-char production", and noted that "other suggestions that have received considerable media attention, in particular “ocean pipes” appear to be ineffective". They concluded that "[climate] geoengineering is best considered as a potential complement to the mitigation of CO2 emissions, rather than as an alternative to it".
Reports into geoengineering have also been published in the United Kingdom by the Institution of Mechanical Engineers and the Royal Society. The IMechE report examined a small subset of proposed schemes (air capture, urban albedo and algal-based CO2 capture schemes), and its main conclusions were that geoengineering should be researched and trialled at the small scale alongside a wider decarbonisation of the economy.
The Royal Society review examined a wide range of geoengineering schemes and evaluated them in terms of effectiveness, affordability, timeliness and safety (assigning qualitative estimates in each assessment). Similarly to Lenton and Vaughan, the report divided schemes into "carbon dioxide removal" (CDR) and "solar radiation management" (SRM) approaches that respectively address longwave and shortwave radiation. The key recommendations of the report were that "Parties to the UNFCCC should make increased efforts towards mitigating and adapting to climate change, and in particular to agreeing to global emissions reductions", and that "[nothing] now known about geoengineering options gives any reason to diminish these efforts". Nonetheless, the report also recommended that "research and development of geoengineering options should be undertaken to investigate whether low risk methods can be made available if it becomes necessary to reduce the rate of warming this century".

Dr.A.Jagadeesh Nellore(AP)

Posted by: Dr.A.Jagadeesh - 31 Jan, 2010