Feasibility of cooling the Earth with a cloud of small spacecraft near the inner Lagrange point (L1)

Abstract

If it were to become apparent that dangerous changes in global climate were inevitable, despite greenhouse gas controls, active methods to cool the Earth on an emergency basis might be desirable. The concept considered here is to block 1.8% of the solar flux with a space sunshade orbited near the inner Lagrange point (L1), in-line between the Earth and sun. Following the work of J. Early [Early, JT (1989) J Br Interplanet Soc 42:567-569], transparent material would be used to deflect the sunlight, rather than to absorb it, to minimize the shift in balance out from L1 caused by radiation pressure. Three advances aimed at practical implementation are presented. First is an optical design for a very thin refractive screen with low reflectivity, leading to a total sunshade mass of Ϸ20 million tons. Second is a concept aimed at reducing transportation cost to $50͞kg by using electromagnetic acceleration to escape Earth's gravity, followed by ion propulsion. Third is an implementation of the sunshade as a cloud of many spacecraft, autonomously stabilized by modulating solar radiation pressure. These meter-sized ''flyers'' would be assembled completely before launch, avoiding any need for construction or unfolding in space. They would weigh a gram each, be launched in stacks of 800,000, and remain for a projected lifetime of 50 years within a 100,000-km-long cloud. The concept builds on existing technologies. It seems feasible that it could be developed and deployed in Ϸ25 years at a cost of a few trillion dollars, <0.5% of world gross domestic product (GDP) over that time.geoengineering ͉ global warming ͉ space sunshade P rojections by the Intergovernmental Panel on Climate Change are for global temperature to rise between 1.5 and 4.5°C by 2100 (1), but recent studies suggest a larger range of uncertainty. Increases as high as 11°C might be possible given CO 2 stabilizing at twice preindustrial content (2). Holding to even this level of CO 2 will require major use of alternative energy sources and improvements in efficiency (3). Unfortunately, global warming reasonably could be expected to take the form of abrupt and unpredictable changes, rather than a gradual increase (4). If it were to become apparent over the next decade or two that disastrous climate change driven by warming was in fact likely or even in progress, then a method to reduce the sun's heat input would become an emergency priority. A 1.8% reduction is projected to fully reverse the warming effect of a doubling of CO 2 (5), although not the chemical effects.One way known to reduce heat input, observed after volcanic eruptions, is to increase aerosol scattering in the stratosphere (6). Deployment of 3 to 5 million tons͞year of sulfur would be needed to mitigate a doubling of CO 2 . This amount is not incompatible with a major reduction in the current atmospheric sulfur pollution of 55 million tons͞year that goes mostly into the troposphere. The approach we examine here to reduce solar warming is to scatter away sunlight in space before it enters the Ear...

Can crop albedo be increased through the modification of leaf trichomes, and could this cool regional climate?

“…In boreal forests, cooling caused by the increased albedo of the new vegetation that follows wildfire exceeds the warming caused by greenhouse gas emissions from the fire and the reduced CO 2 uptake rates that occur during early succession (Randerson et al 2006). Strategies to cool air temperatures by increasing the planetary albedo have been proposed, and include such approaches as injecting reflective aerosols into the stratosphere (Crutzen 2006;Wigley 2006), or deploying space-borne orbital sunshades (Angel 2003). These global albedo manipulations, or geo-engineering proposals, have been criticized as expensive and risky (Brewer 2007).…”

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“…Le dernier projet que nous désirons évoquer est celui proposé par l'astronome de l'université d'Arizona Roger Angel (2006). L'idée consiste à bloquer 1,8 % du rayonnement solaire au moyen d'un parasol constitué de disques de 60 cm de diamètre, fabriqués en matériau optique ultraléger.…”

Risk and uncertainty in hydrometeorological hazards

“…Crutzen, 2006; water droplets: e.g. Ricke et al, 2010); other suggestions include increasing the reflectivity of urban structures (Oleson et al, 2010) or crops , or positioning reflective structures between the earth and sun (Angel, 2006). One advantage of SRM over GHG reduction is that it could potentially cool the climate much more quickly.…”