NOTE: This is an older article from 2012

http://www.livescience.com/23553-asteroid-dust-geoenineering-global-warming.html

Asteroid Dust Could Fight Climate Change on Earth
by Charles Q. Choi
Live Science 
September 28, 2012 

To combat global warming, scientists in Scotland now suggest an 
out-of-this-world 
solution - a giant dust cloud in space, blasted off an asteroid, which 
would act like a sunshade for Earth.

The world is warming and the climate is changing. Although many want to 
prevent these shifts by reducing emissions of greenhouse gases that trap 
heat from the sun, some controversially suggest deliberating manipulating 
the planet's climate with large-scale engineering projects, commonly called 
geoengineering.

Instead of altering the climate by targeting either the oceans or the 
atmosphere, some researchers have suggested geoengineering projects that 
would affect the entire planet from space. For instance, projects that 
reduced the amount of solar radiation Earth receives by 1.7 percent could 
offset the effects of a global increase in temperature of 3.6 degrees 
F (2 degrees C). The United Nations' Intergovernmental Panel on Climate 
Change (IPCC) has noted climate models suggest average global temperatures 
will likely rise by 2 to 11.5 degrees F (1.1 to 6.4 degrees C) by the 
end of this century.

"A 1.7 percent reduction is very small and will hardly be noticeable on 
Earth," said researcher Russell Bewick, a space scientist at the University 
of Strathclyde in Scotland. "People sometimes get the idea of giant screens 
blocking the entire sun. This is not the case ... as [the device] is constantly 
between the sun and the Earth, it acts merely as a very light shade or 
filter."

Shading Earth

One proposal to shade the Earth from the sun would place giant mirrors 
in space. The main problem with this concept is the immense cost and effort 
needed either to build and launch such reflectors or to construct them 
in outer space - the current cost to launch an object into low Earth orbit 
runs into thousands of dollars per pound. Another would use blankets of 
dust to blot out the sun, just as clouds do for Earth. These offer the 
virtue of simplicity compared with mirrors, but run the risk of getting 
dispersed over time by solar radiation and the gravitational pull of the 
sun, moon and planets. [Top 10 Craziest Environmental Ideas]

Now instead of having a dust cloud floating by itself in space, researchers 
suggest an asteroid could essentially gravitationally anchor a dust cloud 
in space to block sunlight and cool the Earth.

"I would like to make it clear that I would never suggest geoengineering 
in place of reducing our carbon emissions," Bewick told LiveScience. Instead, 
he said, "We can buy time to find a lasting solution to combat EarthÂ’s 
climate change. The dust cloud is not a permanent cure, but it could offset 
the effects of climate change for a given time to allow slow-acting measures 
like carbon capture to take effect."

The idea would be to place an asteroid at Lagrange point L1, a site where 
the gravitational pull of the sun and the Earth cancel out. This point 
is about four times the distance from the Earth to the moon.

The researchers suggest outfitting a near-Earth asteroid with a "mass 
driver," a device consisting of electromagnets that would hurl asteroid-derived 
matter away from the giant rock. The mass driver could serve both as a 
rocket to push the asteroid to the L1 point and as an engine to spew out 
sun-shielding dust. [5 Reasons to Care About Asteroids]

The researchers calculate that the largest near-Earth asteroid, 1036 Ganymed, 
could maintain a dust cloud large enough to block out 6.58 percent of 
the solar radiation that would normally reach Earth, more than enough 
to combat any current global warming trends. Such a cloud would be about 
11 million-billion pounds (5 million-billion kilograms) in mass and about 
1,600 miles (2,600 kilometers) wide.

Ganymed has a mass of about 286 million-billion lbs. (130 million-billion 
kg). An asteroid of this size might make one think of disaster movies, 
such as "Armageddon"; however, "rather than destroying the Earth, it could 
be used to help mankind," Bewick said.

Asteroid dust challenges

The main challenge of this proposal would be pushing an asteroid the size 
of Ganymed to the sun-Earth L1 point.

"The company Planetary Resources recently announced their intention to 
mine asteroids," Bewick said. "The study that they base their plans on 
reckons that it will be possible to capture an asteroid with a mass of 
500,000 kilograms (1.1 million lbs.) by 2025. Comparing this to the mass 
of Ganymed makes the task of capturing it seem unfeasible, at least in 
everything except the very far term. However, smaller asteroids could 
be moved and clustered at the first Lagrange point."

Safety is another concern.

"A very large asteroid is a potential threat to Earth, and therefore great 
care and testing would be required in the implementation of this scenario," 
Bewick said. "Due to this, the political challenges would probably match 
the scale of the engineering challenge. Even for the capture of much smaller 
asteroids, there will likely be reservations from all areas of society, 
though the risks would be much less."

Also, there's no way to fully test this dust cloud on a large scale to 
verify its effectiveness before implementing it, "something that is common 
to all geoengineering schemes," Bewick said. "On the global scale, it 
is not possible to test because the test would essentially be the real 
thing, except probably in a diluted form. Climate modeling can be performed, 
but without some large-scale testing, the results from these models cannot 
be fully verified."

Still, if geoengineers did use asteroids to generate clouds, they could 
drastically reduce how much dust the projects spew out "should any catastrophic 
climate response be observed," Bewick said, "with the cloud dispersing 
naturally over time."

The scientists will detail their findings in the Nov. 12 issue of the 
journal Advances in Space Research.

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