[meteorite-list] Asteroid Dust Could Fight Climate Change on Earth

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 25 Feb 2016 14:31:40 -0800 (PST)
Message-ID: <201602252231.u1PMVe0k001263_at_zagami.jpl.nasa.gov>

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 Earth?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.
Received on Thu 25 Feb 2016 05:31:40 PM PST