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PaperclipPerfector  7d ago (text post)   1910 thread views

Friday Fun Thread for November 14, 2025

Be advised: this thread is not for serious in-depth discussion of weighty topics (we have a link for that), this thread is not for anything Culture War related. This thread is for Fun. You got jokes? Share 'em. You got silly questions? Ask 'em.

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Wouldn't actually extending the day with a giant space mirror significantly mess up the climate, plants, and animal behavior?

If you're sending up space mirrors to orbit in order to light your cities, you can just as easily send up space sunshades to the Lagrange point in order to fine-tune global temperature - blocking only 2% of sun light from reaching the earth would cancel global warming. You'd also need less sunshades than space mirrors, since the sunshade always deflects sun light, while the space mirror supposedly only puts light onto the planet for a few hours per day in winter.

But yes, it would mess with plants and animals - though probably less than current light pollution does.

I'm pretty sure that indiscriminate general shading of the planet would substantially disrupt crop production as well as wild flora. For global warming geoengineering purposes you want to increase albedo in the IR range, but retain the spectrum primarily involved in photosynthesis.

If you are only using the mirrors to light your cities, it also seems highly pointless. The biggest direct cost with going to work or school with limited daylight is traffic crashes. If you are only interested in lighting limited areas, we already have the ability to do that it's called a lamp. Using fully shaded and cutoff lensed high-mast lighting limits light pollution and you can install them over the highways leading into the city. If you've ever commuted into a city by car it should be clear the areas where crashes occur due to insufficient lighting are on the unlit highways running in, not the relatively well lit city core.

Using a giant mirror to illuminate an area would also probably not produce the pleasant light people associate with a mild partly sunny day. It would practically be more probably like the light from a full moon, which will not fix the sleep problems and productivity losses associated with short winter days. For people with seasonal affective disorder you need something way stronger either something like a Lumenator or moving closer to the equator. Blasting a whole city with noon-levels of irradiance so a bit of light can trickle in through some peoples windows seems way less efficient than just having people who need it replace their old lights bulbs with corn bulbs.

Agreed on all points, maybe my original answer should have included the remark that both mirrors and sunshades are pretty dumb - but fun to think about.

I'm pretty sure that indiscriminate general shading of the planet would substantially disrupt crop production as well as wild flora.

To be pedantic, the sunshade-at-Lagrange-Point-1 idea would really just dim the sun by 2%. No matter if you use thousands of independent sunshades or one big one, when viewed from Earth it will only occlude a tiny part of the suns disk. Every spot on earth would receive 98% of normal sunlight. This wouldn't "substantially" disrupt crop production, it would just diminish it by around 2% (naively - except in cases where the limiting factor is available water or soil nitrogen/phosphorus or pests/weeds or ...). Making a sunshade that's larger but transmits the red and blue wavelegths relevant for photosynthesis would be smart, but probably even more ludicrously expensive than just having a thin film of aluminum on a polymere membrane which indiscriminately reflects all sun light.

Ultimately, if it matters you could also pretty easily "turn off" a sunshade by flipping it 90° (you probably need this capability anyway, because you have some degree of maneuverability in space using radiation pressure). If you really need a boost to the global growing season a little, you could always just turn it off.

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