Every 5 years or so a 'solution' to climate change along these lines is proposed... presumably with a straight face-

https://journals.plos.org/climate/article?id=10.1371/journal.pclm.0000133

I remember reading a similar paper in the late 1990's and being amazed that no one really took a moment to think it over before attempting to submit it... they did a LOT of solid math that may be vaguely correct, but they never really sat down to think about what it would entail to implement it.

The basic idea is you deposit moon dust in a cloud between the earth and the sun to reduce the solar flux on the surface of the Earth... the people that write these papers never discuss what the reduced solar flux will do to reduce photosynthesis, potentially reducing the uptake of CO2 by plants, nor do they look at how the dust would shift the spectral distribution of light we receive and the impact that might have...

Here are some wonderful examples of their undergraduate level 'analysis':

To achieve sunlight attenuation of 1.8%, equivalent to about 6 days per year of an obscured Sun, the mass of dust in the scenarios we consider must exceed 10^10 kg. The more promising approaches include using high-porosity, fluffy grains to increase the extinction efficiency per unit mass, and launching this material in directed jets from a platform orbiting at L1. A simpler approach is to ballistically eject dust grains from the Moon’s surface on a free trajectory toward L1, providing sun shade for several days or more. Advantages compared to an Earth launch include a ready reservoir of dust on the lunar surface and less kinetic energy required to achieve a sun-shielding orbit.

So... to be clear- IDEALLY the 10 BILLION kg of lunar dust would be transported to the L1 Lagrange point where we would have a platform in orbit that would disperse the dust in directed jets to create the dust cloud that will shade the Earth... But the authors recognize that this may be a wee bit impractical, and being the SERIOUS scientists they are, they own up to the fact that the ideal scenario might not be 'practical'. They suggest it might be 'easier' (but sadly not as 'efficient') to launch the dust directly from the surface of the moon (250,000 miles from the Earth) to the L1 point (~ 1 million miles from the Earth)....

The authors note that Coal dust would be especially efficient for making this sun attenuating cloud- which is a shame because, well, the moon has no known coal beds... nevertheless, they continue to mention how great coal dust would be for this application... They grudgingly resign themselves to the fact that they will have to use moon dust, because -oddly enough- there seems to be a supply of it on the moon... Unfortunately there is a little complication- if they want to keep the total mass of moon dust launched to the 'low' value of 10 billion kg, they really want only the BEST dust... sooo...

As in the figure, the peaks of the attenuation curves for spherical particles as a function of grain size are fairly sharp at just under a micron for most of the materials considered. This result provides a guide to how dust might be mined, sifted or milled to achieve a desired level of attenuation, especially for natural materials that have a broad size distribution. Particle shapes of also impact attenuation by allowing more massive grains with elongated or porous configurations to scatter sunlight more effectively. Since more massive dust particles are less susceptible to the effects of radiation pressure and the solar wind, there may be a benefit to producing dust clouds with these “designer” materials, as discussed below. Production and delivery costs would differ, also impacting the feasibility of each grain type as a solar shield.

The dust may need to mined sifted and milled - the authors acknowledge this MIGHT impact the economics of this approach... the accountants will have to weigh the economic tradeoffs of hand sorting and crafting of 'Artisanal designer dust' that is maximally efficient at blocking sunlight, versus just launching a larger amount of 'locally sourced' free range dust with lower efficiency... such a trade study is- sadly- outside the scope of this important paper... these researchers are 'idea men' and they leave the mundane details to the bean counters.

The researchers provide a very useful graph (figure 1a) showing the optimal particle size if you were to use various materials - for instance, if you had to work with a billion kg of sea salt you probably want a particle size of ~250nm, on the other hand, if you were fortunate enough to have a billion kg of gold (A billion kg of gold would be about the cheapest part of this plan, by the way) you would want particle sizes ~50-100nm. If you had a billion kg of coal dust (yes coal dust again!) then a particle size of ~170nm might be best. Oddly, there is no guidance in the paper as to what the optimal particle size should be if you only have a billion kg of green cheese- perhaps the authors are saving this for a subsequent paper...?

They also provide guidance on optimal particle size if you can tailor the shape of the individual particle- for instance if you make all of the particles to be solid spheres, versus rods, or even hollow tubes... It was very kind of the authors to provide this guidance... That is one less thing we have to figure out to implement this solution! It really reduces the work involved...

Fig 1 provides examples of the attenuation as a function of dust particle size for a variety of materials. Coal dust, (Yup, they are still hung up on coal dust...) which is an efficient absorber, provides the strongest attenuation when dust particles are approximately a few tenths of a micron in radius. Glass, when formed into elongated, hollow tubes, has a peak attenuation when the volume-equivalent radius is about ten microns.

The authors then go on to point one little complicating factor- particles placed at L1 won't conveniently stay where you put them, they will drift from solar wind and photon pressure. This means your dust will drift out of alignment between the sun and Earth in a matter of days... no biggie- you just gotta launch more dust...

When providing shade to Earth, both the attenuation and the persistence of each grain at L1 matter. A simple measure of this joint effect, the cumulative attenuation defined as A0, gives an estimate of the effectiveness of a grain type and quantity for impacting Earth climate. For example, a ten-year reduction of sunlight at Earth equivalent to the Maunder Minimum would have a value of 0.025 attenuation-years, or about 9 attenuation-days. For comparison, Fig 5 shows the cumulative attenuation for 10^9 kg of of dust composed of materials listed in Table 1. Coal dust with radii near 0.1 μm is most effective, in part because of its low density and high scattering efficiency. (Note from RL- Is it just me, or do the authors seem to RESENT the fact there isn't abundant coal dust on the moon?) With a maximum cumulative attenuation of 0.03 days, approximately 300 times more dust of this size and composition (~ 1.5 × 10^11 kg) would need to be delivered to L1 to reproduce the Maunder Minimum.

Over the course of a year you will need a minimum of around 10 billion kg of dust to be launched - ok...MAYBE as much as 100 billion kg (its just an extra zero, and we all know zero is NOTHING!)... per year. There are 260 working days in the year (Union rules will mean the astronauts sifting and loading the the dust bombs get holidays and weekends off)- so the lunar crew simply needs to sift, load and launch 38.5 to 385 MILLION kg of dust per day. This may SOUND like a lot, but that is only because it is... however the authors assure us it is not THAT bad!

For context, 10^11 kg of materials considered here would fill a sphere with a radius of roughly 200 m, comparable to the amount of material excavated per year in a single open-pit mine. The total mass launched into space over human history is considerably less, with estimates under 2 × 10^7 kg.

So, as you can see this proposal is TOTALLY workable, and is NOT in any way just an exercise in creating a sensational paper that will get picked up and repeated breathlessly without any seriousanalysis in the popular press!

It is a SIMPLE strategy to address the threat of global warming! If you don't believe me, just take THEIR word for it...

Because of the simplicity of this strategy—a ready source of dust, a ballistic launch with no subsequent orbit corrections—and its low cost in terms of energy compared with a launch from Earth, it could provide a good alternative to maintaining sun-shielding material at L1.

SEE- you have to appreciate the beautiful simplicity of this concept now!

Roughly 10^10 kg of dust per year is needed for Earth-climate impact, which is approximately 700 times more mass than humans have launched into space. A lower bound on the energy requirement of delivering this material comes from the potential difference between the Earth’s surface and L1,~ 6.3 × 10^7 J/kg. Thus, 10^10 kg of material for a solar shield from Earth would require close to 10^18 J, more than the energy spent in 20,000 Saturn V launches.

Ok... well they goofed here, but every good paper must have at least one tiny error... its actually closer to 5000 times the mass of everything we have launched into space... even IF their energy calculation is correct- that is 28 million kg ... per DAY every day, year after year...from the MOON... from a place where the infrastructure to support it would need to be built from scratch... in a vacuum... with the nearest Dunkin' Donuts a quarter of a million miles away...

WHY do I get the feeling that THIS POST is the first legitimate peer review the paper got? Yet it was regurgitated by press world wide- it is an inexcusable waste of pixels... It sells people the lie that a solution is in the works, so no immediate drastic actions are needed here on Earth... crap like this only does harm.