Cirrus Clouds and Climate Engineering: New Findings on Ice Nucleation and Theoretical Basis

Abstract

Geo-engineering, henceforth referred to as climate engineering, can be described as an intentional intervention on the Earth’s climate system for the purpose of temporarily reducing the increase in surface temperatures due to global warming. While it is generally acknowledged that climate engineering cannot solve the problem of global warming resulting from unrestricted greenhouse gas (GHG) emissions (Launder and Thompson, 2010), it may “buy time” for non-carbon energy systems to dominate global energy production and for GHG emissions to be reduced to safe levels. The longer meaningful global policy decisions on GHG emissions are delayed, the stronger the demand is likely to be for climate engineering research and development. As described by Anderson and Bows (2010), even if an effective global treaty on GHG emissions were to take effect now, it would still be extremely difficult to prevent mean global surface temperatures from rising above 2°C (above which it is argued that the consequences of climate change would be unacceptable). It is thus defensible to argue that some combination of GHG mitigation and climate engineering may be necessary to limit the mean increase in global surface temperatures to 2°C. A modeling study by Arora et al. (2011) also finds that a mean global warming exceeding 2°C may be unavoidable. Using updated GHG emission scenarios and an upgraded Earth system model (which accounts for aerosol effects and represents the carbon-cycle more realistically), the study finds that even under the lowest, most optimistic GHG emission scenario, the global average temperature will still increase more than 2°C (the limit agreed to by various governments in the Copenhagen accord) by 2100. To limit warming to 2°C by 2100, carbon dioxide emissions would need to be reduced to zero over the next 50 years followed by ongoing carbon sequestration (removal of CO2 from the atmosphere) through the end of this century. While few scientists advocate tinkering with the earth’s climate (Schneider 2010), climate engineering of some kind may become a necessity rather than an option. Two types of climate engineering have been recognized: carbon dioxide removal (CDR) strategies and solar radiation management (SRM). CDR approaches can be biological, such as iron fertilization of the oceans to increase phytoplankton uptake of CO2 (Lampitt et al., 2010; Smetacek and Naqvi, 2010), or they can be physically based, such as the direct capture