Ya I think that we'll fail to make any measurable impact on global warming in our lifetimes, because it's much easier to sabotage movements than to invest in them. So we'll inevitably reach for a solution that's a sure thing, and the only one I know of that's scalable is a 1-10 atom thick sunshield at the L1 Lagrange point. It's a problem similar in scope to a light sail, so there's no mystery to it other than trying to grow the dang thing in space.

So if Earth gets a sunshield, it's no more difficult to grow one for Venus. Then eclipsing it and getting it to room temperature would only take a matter of weeks maybe? That would reduce the atmospheric pressure too. Seems like an orders of magnitude easier problem than waiting around for Mars to warm up and pressurize. Although on that note, we could build a giant reflector at the L2 point behind Mars to have room temperature immediately there too.

Looks like a solar sail can be as light as 0.00002 kg/m2, the Earth has a cross section of about 125 million km2, or 1.25e14 m2, so that's 2.5 billion kg or 2.5 million metric tons. Of course there's always a way to make a thinner sail, and we may not need to block all of the light, so I think a million metric tons is a reasonable estimate. Sounds like a lot, but a locomotive is 1000 metric tons, so 1000 train engines or 10,000 heavy launches to save Earth doesn't seem unreasonable. Also we probably only need 1% of that area to have a measurable effect on climate, and that way we wouldn't have to see the shadow either. So we're talking 10 train engines or 100 heavy launches.

https://en.wikipedia.org/wiki/Solar_sail#Materials

Nuking the core is neither sufficient nor necessary for the magnetosphere. Not sufficient because all of the nukes together are orders of magnitude too little to melt it, not necessary because a spinning ball of liquid metal is a really inefficient way to make a magnet.

IIRC one of the plans for an artificial magnetosphere for Mars only needed a 1 GW supply to the magnetic coil.

The core nuking thing I pulled out of my ass but I guess it sounds serious given a sufficiently fantastical context.

Doing a little more reading I came across the superconducting latitudinal "wrap the planet in a solenoid" thing, as well as magnets at L1 etc. I guess that's possible, but that's more of a 2000-years-out sort of set of ideas.

There's a philosophical debate to be had about how far out humans should be thinking when expending resources. If you build for tomorrow, you solve yesterday's problems. If you build for the next millenium, you solve nobody's problems.

> 2000-years-out sort of set of ideas.

Nah, if we really cared we could do either in like a decade or two depending on the Starship timeline.

> If you build for tomorrow, you solve yesterday's problems. If you build for the next millenium, you solve nobody's problems.

Essentially agree; this is why I don’t buy into longtermism: https://kitsunesoftware.wordpress.com/2020/01/08/morality-th...

If our species declared Total War Against The Lack of a Martian Magnetosphere, I could see that happening. However, that implies that our species are in a state of development and coordination that would largely obviate the existential need to create a "Planet B" as people imagine it.

Thanks for the link to the blog post, I enjoyed it.

I'm not firmly in the terraforming camp, but something I'd like to point out is that humans don't need exactly 1 atm. About 0.5 atm would be sufficient. It's analogous to what is found in Bolivia's altiplano. Mar's gravity is sufficient to hold onto oxygen and nitrogen.

True, although if you've fixed the "atmosphere gets stripped away" problem, you've achieved the hard part.

Watch any of the videos on terraforming Venus by Isaac Arthur on YouTube.

A brief summary of proposed methods and their feasibility and a link to further literature may do a bit better at getting your point across than the name of a youtube channel that close to 0% of the people reading this are going to seek out at your say-so.

> a link to further literature

See above.