Giant Space Mirrors...Science-Fiction or Science-Fantastic?

Generic sci-fi poster

Giant space mirrors. They sound like something out of the latest 'end of the world' sci-fi film that will inevitably collide with an asteroid, sending the object hurtling towards Earth to threaten humanities very existence. 

At least, that's what you'd think...

In 2001, American climate scientist Lowell Wood proposed the insertion of ‘giant space mirrors’ into space to the United States government as a strategy to protect Earth from the worsening impacts of climate change. A giant space mirror would attempt to reduce the solar energy the Earth receives by reflecting solar rays back out to space. It is thought that a space mirror system could weaken global insolation from the solar rays at a rate of 1 W m^-2 per decade. This would increase the Earth’s albedo effect whilst balancing out the impact radiative impact of the planet’s ever increasing greenhouse gas emissions.

A theoretical idea of what a space mirror could look like
http://www.nerc.ac.uk/planetearth/stories/302/

Could it help?

The principle reason for the use of space mirrors is that it could have a very positive effect of limiting sea-level rise. Over 634 million people around the world live in an area of low elevation, including 46% of the population of Bangladesh who live within 10m of sea level. Thus, any impact that a geoengineering scheme can have on limiting sea-level rise may be of undeniable assistance to millions on our planet. 

Is it viable?

When assessing the practicality of this notion, one can quickly realise that the insertion of giant space mirrors is flawed. Firstly, Lowell Wood’s proposed space mirror requires a surface area of 600,000 miles². That's over twice the size of the state of Texas! This staggering assessment then leads to the thought of how costly space mirrors may be. The economic viewpoint is examined well by Takanobu Kosugi. His estimates vary depending on how much the planet would need to be cooled by. By 3ᵒC, costs my exceed $240 billion, however by 6ᵒC costs may be up to $1.9 trillion. Kosugi bases these figures too on the fact that mass production of required space parts would lead to reduced costs, a thought that carries no certainty.

To conclude, although it must be admitted that space mirrors would reduce global temperatures, at a cost of $1.9 trillion, they are certainly not a viable option as they do not address other key climate issues such as ocean acidification. Therefore it is with regret that I must label this geoengineering theory as nothing more than a good bit of science-fiction.