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There is recorded evidence from solar eclipses that the moon's shadow has a detectable weather effect.

If we placed a disk in space we could project a cold spot onto the planet and control it's position using the position of the spacecraft. In simple terms warm air moves towards cold, so that could be used to pull weather systems out of their normal track.

  1. What is the smallest disk that would create a 300km shadow
    • Where would be the best place to put it between the earth and sun
  2. What size of effect would you have?
    • Could you move a monsoon from flooded Asia to drought Australia
    • How big would the shadow need to be to have an appreciable effect?
  3. If it was always "on" (i.e. you could turn it "off" by rotating it on edge), would the cooling effect be significant?

It's not going to stop global warming but it might buy some time and help redistribute the water more evenly.

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  • $\begingroup$ Somebody has to hold the disk. It won't stay in place voluntarily. Guys, in principle, you all can assume that every simple suggestion has already been made uncounted times and can be found in more or less serious internet sites. What we need is better understanding for the mechanisms that drive climate change, and how to avoid them. This information is freely available to everyone, just avoid tabloid style sites and pseudoscience. $\endgroup$ – user18607 Jan 10 '20 at 15:30
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    $\begingroup$ Wouldn't the lagrangian point "hold" the disk in place? $\endgroup$ – Martin Jan 10 '20 at 15:36
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    $\begingroup$ Simpsons already did it! $\endgroup$ – Jean-Marie Prival Jan 10 '20 at 15:37
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    $\begingroup$ @Martin, i suggest you ask this in spcace.SE. The only Lagrange point that makes sense is Earth - Sun - L1, and it is unstable (needs continuous correction). Satellites have already been put there. But what we really need to do is cut down greenhouse gas emissions, anything else is not sustainable, or not practicable (a 300km sail in L1 belongs to the latter). $\endgroup$ – user18607 Jan 10 '20 at 16:01
  • $\begingroup$ we have had this question in different flavors many times in the past,baloons-satelites-injecting material into the atmosphere and now the disc,the only thing left is somebody suggesting a cut in CO2. $\endgroup$ – trond hansen Jan 10 '20 at 19:55
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Maybe this question belongs also into the space department here.

The only Lagrange point that makes sense is Earth - Sun - L1, and it is unstable (needs continuous correction). Satellites have already been put there, e.g. SOHO. But what we really need to do is cut down greenhouse gas emissions, anything else is not sustainable, or not practicable (a 300km sail in L1 belongs to the latter). Looking at the problems NASA has with the heat shield of the James Webb telescope i am tempted to say that it is not makeable with current technology.

Geostationary orbit is not an option. The spacing between satellites is much too small and the shield would only cover the equator. Even in geosynchronuous orbits the satellite spacing is down to 73km (https://en.wikipedia.org/wiki/List_of_satellites_in_geosynchronous_orbit) i read, so that's also occupied for such a frond. It'll collide in the ascending/descending nodes with other stuff.

The risks of geo- and climate engineering, e.g. lack of knowledge about possible side effects and the potentially drastical acceleration of global warming when engineering efforts cease (out of money error ;-)) and the time when they were in effect has not been used to cut down greenhouse gas emissions, are huge.

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It would have to be a hell of a big disc, and in a geostationary orbit. No, it's not practical, we can never control the weather with satellites in space. It's a non-starter. What might be done with satellites is to reflect the sun's rays into frostbound valleys where there is a small town in shadow which is not getting the benefits of spring as early as other nearby towns. It could also be used for night time street lighting. However, I doubt whether the results would justify the expense, and there are bound to be people who wouldn't like it. The things you mention in your question are not possible.

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  • $\begingroup$ I agree a satellite in geostationary orbit would need to be HUGE, but one at the largrange point could be much smaller. $\endgroup$ – Martin Jan 10 '20 at 16:43

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