4 ms·

So how many sunshades (or square meters of mirror foil) could we get to orbit to regulate global warming?

by dandare 10y ago

aetherson 10y ago
The earth, as it turns out, is pretty big. I don't think that you can get meaningful amounts of sunshades into orbit via rocket launches from Earth, even really, really efficient rocket launches from Earth. As a wild-and-crazy concept, doing the lunar space elevator thing that Stross mentions in his blog post would allow you to build a manufacturing facility on the moon that turned regolith into a sunshade and then ship them up the lunar space elevator and drop them off into Earth orbit at a moderately reasonable cost. If you aren't too concerned about the mass of a sunshade, there are lots of ways to constitute them, so this seems like it would be one of the easier manufacturing jobs you might imagine locating on the Moon.
BurningFrog 10y ago
Gold is supposedly the most malleable metal. One ounce - the size of a quarter - can be hammered out to 10 square meters. I'll let someone else do the math.
- mathgorges 10y ago
  The radius of Earth (according to Google) is 6371 km π * 6371^2 ≈1.28e8 km^2 = 1.28e11 m^2 = 1.28e10 oz of gold So, you would need 800 million pounds of gold, which would cost (at current spot price of 1324.80/oz) almost 18 trillion dollars. Gold is probably not the best material for this
  - pacificmint 10y ago
    800 million pounds is about 360,000 metric tons. The total amount of gold we have mined so far is somewhere around 170,000 metric tons. So if you used all the gold in the world, you'd only have about half of what you need. At the same time, I was surprised that it is even in the same ballpark.
  - BurningFrog 10y ago
    Thanks for the math help :) That's looks like the size to cover the entire planet and completely remove all sunlight. But to counteract global warming, we'd need a much smaller area. If it's 1%, we're down to a mere $180B. I'm sure you're right that other materials would be far more economical. My gut says Aluminum.
    - maxander 10y ago
      Given that the costs of global warming are talked in the trillions, this means that this silly thought experiment would actually be a rationally economical solution. Which just illustrates how terrible global warning really is, I suppose.
philipkglass 10y ago
Suppose that you can build a reflector surface with a 10 micron aluminum foil (27 grams per square meter) and an additional 13 grams of support mass to keep it rigid/oriented, for a total mass of 40 grams per square meter. Near Earth but outside atmosphere the solar constant is about 1366 watts per square meter. That puts an upper bound on how much warming you can prevent per m^2; in reality the Earth's atmosphere and surface already reflect a fair part of that energy without absorbing it. If you send the reflectors to geostationary orbit they'll be in sunlight constantly, but I don't know if their full penumbra will actually fall on Earth, plus that reduces the deliverable payload mass. Instead let's make another unrealistic simplifying assumption for the sake of argument: pretend that the shade array goes to LEO but it's reflecting sunlight away from Earth 100% of the time. At 40 grams per square meter of reflector and 1366 watts per square meter that's an upper bound of 34.15 watts per gram or 34.15 megawatts per tonne of avoided insolation. With one expendable launch of 500 tonnes to LEO that's an upper bound of 17,075 megawatts of avoided insolation per launch. In 2007 the IPCC estimated the net anthropogenic component of radiative forcing for the Earth system at ~1.5 watts/m^2, or 765,108,000 megawatts altogether (1.5 * 510072000 * 10^6 watts). Using the assumptions previously given, one maximum-payload launch could mitigate about 0.002% of anthropogenic radiative forcing. Adjust the achievable mitigation upward proportionately if you think that the shield system can be implemented with less mass and adjust it downward if you want to replace my optimistic upper bounds assumptions with more realistic (lower) ones.

So how many sunshades (or square meters of mirror foil) could we get to orbit to regulate global warming?

by dandare 10y ago

So how many sunshades (or square meters of mirror foil) could we get to orbit to regulate global warming?

The earth, as it turns out, is pretty big. I don't think that you can get meaningful amounts of sunshades into orbit via rocket launches from Earth, even really, really efficient rocket launches from Earth. As a wild-and-crazy concept, doing the lunar space elevator thing that Stross mentions in his blog post would allow you to build a manufacturing facility on the moon that turned regolith into a sunshade and then ship them up the lunar space elevator and drop them off into Earth orbit at a moderately reasonable cost. If you aren't too concerned about the mass of a sunshade, there are lots of ways to constitute them, so this seems like it would be one of the easier manufacturing jobs you might imagine locating on the Moon.

BurningFrog 10y ago

Gold is supposedly the most malleable metal. One ounce - the size of a quarter - can be hammered out to 10 square meters. I'll let someone else do the math.

mathgorges 10y ago
The radius of Earth (according to Google) is 6371 km π * 6371^2 ≈1.28e8 km^2 = 1.28e11 m^2 = 1.28e10 oz of gold So, you would need 800 million pounds of gold, which would cost (at current spot price of 1324.80/oz) almost 18 trillion dollars. Gold is probably not the best material for this
- pacificmint 10y ago
  800 million pounds is about 360,000 metric tons. The total amount of gold we have mined so far is somewhere around 170,000 metric tons. So if you used all the gold in the world, you'd only have about half of what you need. At the same time, I was surprised that it is even in the same ballpark.
- BurningFrog 10y ago
  Thanks for the math help :) That's looks like the size to cover the entire planet and completely remove all sunlight. But to counteract global warming, we'd need a much smaller area. If it's 1%, we're down to a mere $180B. I'm sure you're right that other materials would be far more economical. My gut says Aluminum.
  - maxander 10y ago
    Given that the costs of global warming are talked in the trillions, this means that this silly thought experiment would actually be a rationally economical solution. Which just illustrates how terrible global warning really is, I suppose.

philipkglass 10y ago

Suppose that you can build a reflector surface with a 10 micron aluminum foil (27 grams per square meter) and an additional 13 grams of support mass to keep it rigid/oriented, for a total mass of 40 grams per square meter. Near Earth but outside atmosphere the solar constant is about 1366 watts per square meter. That puts an upper bound on how much warming you can prevent per m^2; in reality the Earth's atmosphere and surface already reflect a fair part of that energy without absorbing it. If you send the reflectors to geostationary orbit they'll be in sunlight constantly, but I don't know if their full penumbra will actually fall on Earth, plus that reduces the deliverable payload mass. Instead let's make another unrealistic simplifying assumption for the sake of argument: pretend that the shade array goes to LEO but it's reflecting sunlight away from Earth 100% of the time. At 40 grams per square meter of reflector and 1366 watts per square meter that's an upper bound of 34.15 watts per gram or 34.15 megawatts per tonne of avoided insolation. With one expendable launch of 500 tonnes to LEO that's an upper bound of 17,075 megawatts of avoided insolation per launch. In 2007 the IPCC estimated the net anthropogenic component of radiative forcing for the Earth system at ~1.5 watts/m^2, or 765,108,000 megawatts altogether (1.5 * 510072000 * 10^6 watts). Using the assumptions previously given, one maximum-payload launch could mitigate about 0.002% of anthropogenic radiative forcing. Adjust the achievable mitigation upward proportionately if you think that the shield system can be implemented with less mass and adjust it downward if you want to replace my optimistic upper bounds assumptions with more realistic (lower) ones.