A SUNSHADE TO COOL THE EARTH?
Well, I watched the sky on the night of October 14 to test Wiley Brooks' prediction, and the only thing appearing even remotely like a "Federation of Light 2000-mile long Space Craft" was the full Moon. In fact, it's hard to come up with a better 8-word description of the full Moon, except perhaps by replacing "2000-mile" with "2160-mile", the exact lunar diameter. So we had best forget about hitching a ride with extraterrestrials to remote Earthlike planets, and instead save the planet we're stuck on.
That means stopping global warming as soon as possible. The buildup of carbon dioxide in the atmosphere resulting from the globalization of fossil-fuel burning and deforestation shows no sign of slowing down. Recent climatic changes - the increased pace of Arctic ice meltdown, rising frequency of major hurricanes and killer heat waves, and the accelerating retreat of mountain glaciers - all signal that the global temperature is rising in lockstep with rising CO2, in accordance with predictions based on global climate models. While the atmospheric level of CO2 is still below 400 ppm (parts per million), it could reach 1000 ppm before the end of the next century, a level last seen at the start of the Eocene Period 60 million years ago. That age was characterized by tropical climate from pole to pole. If the past is guide to the future, the world is on the threshold of a mass extinction that should be somewhat similar to at least nine mass extinctions caused by rapid global warming in the last 600 million years, triggered by CO2 released during the lava flows that produced flood basalts (Ref. 1).
Perhaps more alarming than the impending CO2 level is its rate of increase, a geologically unprecedented rate that could overwhelm the capacity of the oceans to absorb and buffer against acidification, making the next mass extinction more deadly than its predecessors. Thus the industrial addition of CO2 to the atmosphere presents the world with two environmental problems: Problem 1 is higher temperatures, Problem 2 is more acidic oceans. In the best of all possible futures, both problems would be addressed by cutting back CO2 emissions to preindustrial levels. But even if this could be achieved instantly, the global temperature would continue to rise until the massive CO2 injection of the 20th Century has worked its way through the ocean-atmosphere system, a process that could take a century or more. In other words, the effects of global warming are upon us already. Instant action to rein in CO2 emissions might avert ocean acidification and mass extinctions, but would not stop global warming in its tracks.
What can humanity do to stop the relentless increase in global temperature? One obvious way is to put up a sunshade, a well known means of cooling off in hot weather. A 1000-mile-wide sunshade in space could reduce the sunlight reaching Earth by about 2%, enough to compensate for the warming that would otherwise take place if CO2 were to stabilize at 550 parts per million (twice the pre-industrial level). This idea was first floated 20 years ago by James T. Early, a scientist at Lawrence Livermore National Laboratory, who proposed placing the sunshade between Earth and Sun near the L1 Lagrange point (1.5 million km altitude). There it would stay put with a minimum of station keeping, because the forces exerted on it by Sun and Earth balance almost exactly. At L1, the sunshade would appear silhouetted against the disk of the sun regardless of the observer's location, and would therefore shade the entire globe evenly. Early's sunshade would be a thin, grooved glass sheet that refracts the sun's rays by half a degree, just enough to bypass the Earth.
Wow, this by itself could stop global warming, so why hasn't NASA run with the idea? It must have been deterred by the fine print in Early's paper (Ref. 2). The sunshield's mass would be 100 million tons which, at today's launch costs of $20,000 per kg to high orbit, would take ten quadrillion dollars just to pay the transportation bill. Early suggested fabricating it from lunar materials which would take much less energy to transport (and therefore less money), bringing the price down to perhaps a few trillion dollars. But that would first require the establishment of a Moon base, something NASA is not expecting to complete before 2024. So why start talking about sunshades already?
Some people are not waiting for NASA to build a Moon base. Roger Angel recently proposed cooling the Earth by deploying a cloud of fresnel lenses rather than one huge sunshade (Ref. 3). He demonstrated the required diffraction properties of a candidate lens material using private rather than NASA funding (Ref. 4). Each one of Angel's 16 trillion lenses would be a 60-cm diameter silicon nitride screen, having a mass of only 1.2 grams. Totaling only 20 million tons, Angel's concept reduces by a factor of five the mass needed at L1 to stop global warming. Even though it will still cost a few trillion dollars, Angel's project can begin immediately because his lenses can be launched from Earth. Unfortunately the launcher he has chosen to reduce costs, an electromagnetic "coil gun", must exert 4,000 gees acceleration on the lenses to achieve escape velocity. It is far from obvious that the lenses, to be launched in stacks of 800 thousand, would survive the crushing forces without shattering, and without being pressure-welded together by the launch experience, unable to separate from each other for deployment.
Surely there are better sunshade plans just waiting to be hatched. How about a network of carbon nanotubes woven into diffracting screens? Early's glass lens would be 10 microns thick (1/5 the thickness of a human hair), and Angel's silicon nitride lenses would be 1.06 microns thick. But carbon nanotube lenses might be 100 times thinner than that, potentially reducing total sunshade mass to 200,000 tons and launch costs to ten billion dollars. How about transporting the lenses to space with a space elevator, a thin ribbon stretching from the ground to beyond geostationary orbit? A payload carrier powered by on-board solar panels could crawl up this ribbon at arbitrarily low accelerations, reducing not only the stresses on the stack of lenses but also the carbon footprint of the entire launch operation. This is something the next President of the United States could direct NASA to investigate. Global warming is a global crisis that calls for all hands on deck, even NASA's, and all minds thinking outside their traditional boxes.
References
1. "Under a Green Sky: Global Warming, the Mass Extinctions of the Past, and What They Mean for Our Future", by Peter D. Ward, Smithsonian Books, 2007.
2. "Space-based solar shield to offset greenhouse effect", Journal of the British Interplanetary Society, December 1989, pages 567-569.
3. "Feasibility of cooling the Earth with a cloud of small spacecraft near the inner Lagrange point (L1)", Proceedings of the National Academy of Sciences, November 14, 2006, pages 17184-17189.
4. "Space Sunshield", episode in "Project Earth" TV series, Discovery Channel, 2008.
That means stopping global warming as soon as possible. The buildup of carbon dioxide in the atmosphere resulting from the globalization of fossil-fuel burning and deforestation shows no sign of slowing down. Recent climatic changes - the increased pace of Arctic ice meltdown, rising frequency of major hurricanes and killer heat waves, and the accelerating retreat of mountain glaciers - all signal that the global temperature is rising in lockstep with rising CO2, in accordance with predictions based on global climate models. While the atmospheric level of CO2 is still below 400 ppm (parts per million), it could reach 1000 ppm before the end of the next century, a level last seen at the start of the Eocene Period 60 million years ago. That age was characterized by tropical climate from pole to pole. If the past is guide to the future, the world is on the threshold of a mass extinction that should be somewhat similar to at least nine mass extinctions caused by rapid global warming in the last 600 million years, triggered by CO2 released during the lava flows that produced flood basalts (Ref. 1).
Perhaps more alarming than the impending CO2 level is its rate of increase, a geologically unprecedented rate that could overwhelm the capacity of the oceans to absorb and buffer against acidification, making the next mass extinction more deadly than its predecessors. Thus the industrial addition of CO2 to the atmosphere presents the world with two environmental problems: Problem 1 is higher temperatures, Problem 2 is more acidic oceans. In the best of all possible futures, both problems would be addressed by cutting back CO2 emissions to preindustrial levels. But even if this could be achieved instantly, the global temperature would continue to rise until the massive CO2 injection of the 20th Century has worked its way through the ocean-atmosphere system, a process that could take a century or more. In other words, the effects of global warming are upon us already. Instant action to rein in CO2 emissions might avert ocean acidification and mass extinctions, but would not stop global warming in its tracks.
What can humanity do to stop the relentless increase in global temperature? One obvious way is to put up a sunshade, a well known means of cooling off in hot weather. A 1000-mile-wide sunshade in space could reduce the sunlight reaching Earth by about 2%, enough to compensate for the warming that would otherwise take place if CO2 were to stabilize at 550 parts per million (twice the pre-industrial level). This idea was first floated 20 years ago by James T. Early, a scientist at Lawrence Livermore National Laboratory, who proposed placing the sunshade between Earth and Sun near the L1 Lagrange point (1.5 million km altitude). There it would stay put with a minimum of station keeping, because the forces exerted on it by Sun and Earth balance almost exactly. At L1, the sunshade would appear silhouetted against the disk of the sun regardless of the observer's location, and would therefore shade the entire globe evenly. Early's sunshade would be a thin, grooved glass sheet that refracts the sun's rays by half a degree, just enough to bypass the Earth.
Wow, this by itself could stop global warming, so why hasn't NASA run with the idea? It must have been deterred by the fine print in Early's paper (Ref. 2). The sunshield's mass would be 100 million tons which, at today's launch costs of $20,000 per kg to high orbit, would take ten quadrillion dollars just to pay the transportation bill. Early suggested fabricating it from lunar materials which would take much less energy to transport (and therefore less money), bringing the price down to perhaps a few trillion dollars. But that would first require the establishment of a Moon base, something NASA is not expecting to complete before 2024. So why start talking about sunshades already?
Some people are not waiting for NASA to build a Moon base. Roger Angel recently proposed cooling the Earth by deploying a cloud of fresnel lenses rather than one huge sunshade (Ref. 3). He demonstrated the required diffraction properties of a candidate lens material using private rather than NASA funding (Ref. 4). Each one of Angel's 16 trillion lenses would be a 60-cm diameter silicon nitride screen, having a mass of only 1.2 grams. Totaling only 20 million tons, Angel's concept reduces by a factor of five the mass needed at L1 to stop global warming. Even though it will still cost a few trillion dollars, Angel's project can begin immediately because his lenses can be launched from Earth. Unfortunately the launcher he has chosen to reduce costs, an electromagnetic "coil gun", must exert 4,000 gees acceleration on the lenses to achieve escape velocity. It is far from obvious that the lenses, to be launched in stacks of 800 thousand, would survive the crushing forces without shattering, and without being pressure-welded together by the launch experience, unable to separate from each other for deployment.
Surely there are better sunshade plans just waiting to be hatched. How about a network of carbon nanotubes woven into diffracting screens? Early's glass lens would be 10 microns thick (1/5 the thickness of a human hair), and Angel's silicon nitride lenses would be 1.06 microns thick. But carbon nanotube lenses might be 100 times thinner than that, potentially reducing total sunshade mass to 200,000 tons and launch costs to ten billion dollars. How about transporting the lenses to space with a space elevator, a thin ribbon stretching from the ground to beyond geostationary orbit? A payload carrier powered by on-board solar panels could crawl up this ribbon at arbitrarily low accelerations, reducing not only the stresses on the stack of lenses but also the carbon footprint of the entire launch operation. This is something the next President of the United States could direct NASA to investigate. Global warming is a global crisis that calls for all hands on deck, even NASA's, and all minds thinking outside their traditional boxes.
References
1. "Under a Green Sky: Global Warming, the Mass Extinctions of the Past, and What They Mean for Our Future", by Peter D. Ward, Smithsonian Books, 2007.
2. "Space-based solar shield to offset greenhouse effect", Journal of the British Interplanetary Society, December 1989, pages 567-569.
3. "Feasibility of cooling the Earth with a cloud of small spacecraft near the inner Lagrange point (L1)", Proceedings of the National Academy of Sciences, November 14, 2006, pages 17184-17189.
4. "Space Sunshield", episode in "Project Earth" TV series, Discovery Channel, 2008.
Labels: global warming, NASA, space sunshade
posted by Michael Pelizzari at 12:50 AM
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