By now, many around the world will have realized we are experiencing climate change, thanks to our predilection for burning fossil fuels. The politicians have made their usual platitudinous statements that this problem will be solved, say twenty years out. It is now thirty years since these statements started being made, and we find ourselves worse off than when the politicians started. Their basic idea seems to be that the crisis gets unmanageable in, say, sixty years, so we can leave it for now. What actually happens is, er, nothing in the immediate future. It can be left for politicians thirty years out from now. Then, when the thirty years has passed it is suddenly discovered that it is all a little harder than expected, but they can introduce things like carbon trading, which employs people like themselves, and they can exhort people to buy electric cars. (If you live somewhere like Calgary and want to go skiing at Banff, it appears you need to prepare your car four hours before using it, or maintain battery warmers because the batteries do not like the cold one bit.)
Bromley et al. in PLOS Climate (https://doi.org/10.1371/journal.pclm.0000133) have a solution. To overcome the forcing of the greenhouse gases currently in the atmosphere, according to this article all you have to do is to reduce the solar input by 1.8%. What could be simpler? This might be easier than increasing the albedo.
The question then is, how to do this? The proposed answer is to take fine fluffy dust from the Moon and propel it to the Earth-Sun L1 position. This will provide several days of shading, while the solar winds and radiation slowly clear this dust away. How much such dust? About ten billion kg, which is about a thousand times more mass than humans have currently ever sent into space. Over a ten year period, this corresponds to a sphere of radius roughly 200 m, which corresponds to the annual excavation from many open pit mines on Earth. The advantage of using the Moon, of course is that the gravitational force is about 17% that of Earth so you need much less energy to eject the dust. The difficulty is that you have to put sufficient equipment on the Moon’s surface to gather and eject the dust. One difficulty I see here is that while there is plenty of dust on the Moon, it is not in a particularly deep layer, which mean the equipment has to keep moving. Larger fluffy particles are apparently preferred, but fluffy particles would probably be formed in a fluid eruption, and as far as we know, that is less likely on the Moon.
Then there are problems. The most obvious one, apart from the cost of the whole exercise, is the need for accuracy. If the dust is outside the lines from the edges of the Sun-Earth, then the scattering can increase the solar radiation to Earth. Oops. The there is another problem. Unlike L4 and L5, which are regions, L1 really is a point where an object will corotate. If a particle is even 1 km off the point, it could drift away by up to 1000 km in a year, and if it does that, perforce it will drift out of the Sun-Earth line, in which case the dust will be enhancing the illumination of Earth. Again, oops. Added to this are a small number of further effects, the most obvious being solar wind and radiation pressure which will push objects away from L1.
The proposed approach is to launch dust at 4.7 km/s towards L1, and do it from the Moon when the Moon is close to being in line, so that the dust, as it streams towards L1 continues to provide shielding while it is in-flight. The launching would require 10^17 J, which is roughly the energy generated by a few square km of solar panels. One of the claimed advantages of this is that the dust could be sent in pulses, timed to cool places with major heat problems. It is probably unsurprising that bigger particles are less efficient at shading sunlight, at least on a per mass scale, simply because there is mass behind the front surface doing nothing. Particles too small neither last very long in the required position, nor do they offer as much shielding. As it happens, somewhat fortuitously, the best size is 0.2 μm, and that happens to be the average size of lunar regolith dust.
One of the advantages claimed for this method is that once a week or so is over, there are no long-term consequences from that dust. One of the disadvantages is that which goes for any planetary engineering proposal: What is the minimum agreement required from the world population, how do you get it, and what happens if someone does it anyway? Would you vote for it?