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Comment by WhompingWindows | Hacker News Reader

With the rapidly declining costs of getting payloads to outerspace, I think we should discuss blocking radiation from the sun in some way. We clearly are not going to transition our entire energy system fast enough, but using mirrors/reflectors is a reversible and reasonable way to slow the warming of the planet.

Let's say we take rockets from SpaceX out to 2050: wouldn't that be ample time for cost declines to make trillions of small mirrors possible?

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This might help contain temperature changes, but it won't prevent ocean acidification due to rising CO2 levels. I'm curious what percent of the damage is done by CO2 levels vs directly by temperature.

But which metric do you use for "percent of damage" ?

Even if it was actually feasible to regulate how much sun the Earth gets you'd have to consider these points:

1) Climate lag. There are some 40 years of lag between emissions and changes to the climate. Even if stopped all human emissions today temperatures would keep rising for 40 years.

2) Climate feedbacks. There are a number of systems (methane, arctic ice, etc) that will keep altering the climate even if we stopped all emissions today.

The next 100 or so years are going to be rough no matter what humanity does.

If you run the numbers you'll see that this is not a viable option. It's too expensive to get enough payload in space, the earth can't afford it.

I mean if you're making mirrors, why do we need to put them in space at great cost? Just put them on earth. The cost of the actual mirrors is basically zero compared to to the cost of putting that mirror in orbit. The earth mirrors might be slightly less efficient but you can just make up for that with more mirrors.

I'm not necessarily disagreeing with your conclusions here, but I'd like to discuss this a little more if that's ok with you.

> It's too expensive to get enough payload in space

Full disclosure: I'm a pretty big SpaceX fan.

At first glance, SpaceX is currently charging about $1000USD/kg to LEO. It's widely believed that SpaceX's internal cost is a fairly small fraction of that; let's assume it's $500USD/kg to LEO.

The Big One will be Starship + Superheavy, assuming it flies. That stack will be entirely reusable, so its base cost (ignoring build amortization of the build) will be fuel + operational expenses.

Musk said that he hopes that Starship + Superheavy will be able to deliver 120 metric tons to low earth orbit for 4x the price of a 747 flight, or about $2 million USD, which yields a cost of less than $20USD/kg to LEO.

A lot of speculation there, and $20/kg is still a lot more expensive than mirrors on the ground...maybe. How much more effective would mirrors be stationed at Lagrange Point 1?

I suspect your overall conclusion is correct though.

The earth is kinda big. The sun strikes over 49,000,000 square miles at any given moment. A solid surface shade blocking 1% would need to be nearly half a million square miles if we could hold it in place like at lagrange 1. If we could launch a fuel that burns into a gas that can effectively block/reflect light that reduces the mass to about 250 sq. miles of fuel times whatever is the necessary density of the gas cloud.

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