5 hours ago, mistermack said:

That sounds like a heck of a lot. Were they talking about a shield that could completely block out the Sun? To "correct" the climate, it would surely be only necessary to block a small proportion of the total sunlight. At a guess, less than one percent. 

My source - Sanchez and McInnes - were looking at blocking the amount estimated to be needed - about 1.7% of sunlight.

 

Quote

The scale of the geoengineering scheme studied here is clearly vast, and requires a leap of the imagination over current space engineering endeavours. It has been argued nevertheless that the cost of such an endeavour will still be comparable to other terrestrial geoengineering proposals [2]. In terms of human engineering projects, the mass and scale of the sunshades will also be similar to current terrestrial civil engineering projects such as the Chinese Three Gorges Dam [20], and require a mass production of coated thin material equivalent to the current world decadal production of aluminium foil.

As much mass as Three Gorges Dam, but in space. I suppose the grand space dreamers will suggest we "just" mine the moon or asteroids.

I didn't see any estimates of how long the hardware would last or how much ongoing maintenance; given how speculative it is that might look like a minor detail. I think that without extraordinary advances in space capabilities (and even then) this isn't a climate solution we can use.

 

It's certainly pie-in-the-sky at the moment, there's no doubt about that. In the future though, (a long time in the future) it will surely be a more practical proposition. Mining the Moon or asteroids would be the only practical way that it could happen, and that's probably at least a hundred years away. Probably two hundred. 

You would think that whether it's via nuclear, or via renewables with energy storage, the global emissions of CO2 will be under control by then, so whatever the climate is doing, I can't imagine that space reflectors on that scale will ever be worth the effort and investment needed. 

For a tiny fraction of what it would cost, you could cut out all CO2 emissions worldwide with a mix of nuclear and renewables. Cars and trucks are going to be electric fairly soon anyway.