The last SRM Method …. Spaced Based

The idea of putting sunshades in space was first proposed by James Early in 1989 and since then the idea has been developed and proposed as a solution to climate change.

Space Based SRM would work to reduce the amount of solar energy entering the Earth by placing reflective materials such as dust particles or discs into orbit around the earth. The effectiveness of space based SRM is pretty much indisputable and unlike other SRM methods there is no physical limit of the extent of solar radiation reduction.

Issues arise when the logistics of space based SRM methods are taken into consideration as both the costs and magnitude of the methods are very high.

Image 1

The first proposal by James Early mentioned above consisted of one single sun shield situated at the Sun Earth Lagrangrian point 1 (See image 1). The shield would measure 2000km in width and be 10μ thick in order to block 2% of the Sun’s solar radiation. The cost of implementing this method is between $1-10 trillion – not only is this range huge and therefore vague, the minimum cost of $1 trillion dollars is also huge and as a result other methods are likely to be considered over a space based shield. Moreover, the method becomes less feasible when the amount of work that would be needed to construct the shield in space is factored into the equation alongside the very high costs.

Addressing this issue is the developments of sunshields that are smaller in size but reflect the same amount of solar radiation (McInnes, 2010)– these highly engineered refractors are however significantly more expensive to produce thus although the magnitude of the space mirror may be reduced the costs would be even higher.

Alternatively and probably a more likely scenario would be the use of a large number of smaller sized discs with the same total surface area as that of one single disc (McInnes, 2010). The smaller sized discs could be free flying independent elements or they could form a large occulting disc (see image 2 below). An absorbing occulter uses lunar or near Earth asteroid material and the total occulting area grows over a period of 50-100 years to match the required reductions in solar insolation as carbon emissions rise.

Image 2 - Occulting Disc 

Roger Angel’s (2006) research proposes a cloud of free flying spacecraft, 100,000km in length, that consists of transparent material that deflects the path of radiation in order to reduce the suns heat by 1.8%. A total of 20million sunshades and launches would be required at the again very high cost of $600 billion.  In addition to this a further $30 billion would be required to build a launcher and $150 billion would be needed to cover the energy costs to use it.

Although space based methods are located outside the Earth, there are still environmental effects caused as a result of the methods. Lunt et al.’s (2008) study shows that the SRM world would be significantly different to a pre industrial world in a number of ways. Firstly Arctic sea ice would be lower, the ENSO would have a reduced amplification, the Atlantic Ocean overturning would be stronger and the hydrological cycle’s intensity would be less intense, most notably in the tropics. Such changes could have significant repercussions, ecologically and on societies, however these changes would be less catastrophic than those that would occur from global warming left unaddressed