Are space sunshades the solution?

Another suggested way to mitigate global warming is using small spacecrafts, placed between Earth and sun as a ‘sunshade for the earth’. This method is analysed in an article by Roger Angel (2006). The idea comes from observations of great volcanic events, after which particles in the atmosphere lead to a cooling effect by scattering and reflecting sunlight. The same idea was used for the sulphur injections, which I described before. However, shielding the earth with space sunshades does not have the same negative side effects for the environment that sulphur has. 

The proposed location for the sunshade is near the Earth-sun inner Lagrange point (L1), which is a point between sun and Earth where theoretically gravity alone makes sure the sunshade remains stationary. The penumbra of the sunshade would cover the whole Earth in this position. However, little spacecrafts rather than just particles are necessary to stay in one formation.

The advantage of this technology is, that neither ocean nor atmosphere is modified, which makes this method more environmentally friendly. Furthermore Angel (2006) argues, that the results are easier to predict than the results for other methods, as only one factor (solar radiation) is changed.

The downside is, that it requires a sunshade at a really large scale, which is not only difficult to achieve technically but is also very expensive.

(source: Angel 2006: 17184)

 The idea is to launch many individual ‘flyers’ (Angel 2006) from the Earth. This way there is no need for a single large sunshade. Still there is a very high cost for transportation. Angel (2006) estimates it to be $50/kg. The whole project would have a cost of 1 trillion $, with a cost average of 100 billion/year (‘0.2% of current world gross domestic product’ Angel 2006: 17189). Also it is not enough to just bring the flyers away from the atmosphere. Additional energy is needed to reach the final location. An optimistic goal is that the flyers will stay in place for approximately 50 years, if the technology is improved further and works as ideal as it is hoped. After this they have to be replaces, but a life period for several decades would be a great achievement compared to other techniques. Angel (2006) further suggests that 20 launchers are needed, each launching 20 million flyers, one every 5 minutes. Launching the flyers obviously requires energy, but the positive effect they have once they reach their destination outweighs this negative on climate.

To sum it up, a cloud of small sunshade has the potential to mitigate the current trend of global warming by scattering incoming solar radiation. The environmental impacts, apart from the energy that is needed to produce and launch the flyers, are by far smaller than the impacts of e.g. ocean fertilization or sulphur injections, which makes the idea even more interesting.

However, this is one of the methods with the highest technological level and very high costs. Even if the costs can be reduced to the goal of 50$/kg with more research, the method is still more expensive than most other geoengineering ideas. Therefore I think, that even if the methods works good in theory, the high costs could be the reason why governments might not want to use it. Another question is, how big are the cost if we do nothing? Adaptation to climate change later might be even more expensive, than trying to mitigate it now. So, shouldn’t we make an efforts to raise the money for geoengineering now, rather than paying for the consequences later?

Literature:

Angel, R. (2006) ‘Feasibility of cooling the Earth with a cloud of small spacecraft near the inner Lagrange point (L1)’ PNAS, 103, 46, 17184-17189.
available online: http://www.pnas.org/content/103/46/17184.full.pdf