A cloud of dust suspended between the sun and the earth may be able to block enough sunlight to combat global climate change. Should this option prove necessary, grains about one micron in size, composed of lunar dust and launched from the surface of the moon, would be a good option, researchers wrote from the University of Utah and the Smithsonian in the United States in early February in the science journal PLOS Climate.
Sunlight that does not reach the surface of the earth cannot heat the earth either. With that idea in mind, techniques to intercept 1 to 2 percent of sunlight are being investigated. A dust cloud in space is one of the options, others are making clouds more reflective, releasing particles into the stratosphere or placing a sun shield in space. The collective term for this type of intervention is geoengineeringalso climate engineering named. The ideas are controversial because the effect on the climate is difficult to predict and the consequences can be enormous. Almost all of these techniques are still in a very early stage of research.
Gold
The idea of a dust cloud has been looked at before. It is possible to block sunlight with such a cloud, but it is difficult, among other things, that the dust quickly disperses. This new study compared grains of different materials – including glass, gold and lunar dust – and their shapes and their performance at different locations in space. Considered were where the grains should come from, and how much energy it takes to launch a large cloud of dust.
A grain of a micrometer (0.001 millimeter) in size with a porous shape would work best, the researchers write. Very small grains, a few nanometers in size, do reflect a lot of light, but they also do this partly forwards instead of backwards, as desired. In addition, they are not very resistant to the forces associated with the radiation of the sun. Grains of a few micrometres hold up better, but they do not reflect light as efficiently.
The trajectory in which the cloud has to do its work is located at Lagrange point 1 (L1). An efficient place, because all photons that pass there are on their way to the earth’s surface. It is also a more or less stable point, where the forces of the sun and earth are in balance. However, under forces from the moon, the dust cloud still drifts apart, after about a week the effect is no longer enough. This means that the temperature reduction can be used seasonally, but also that an almost continuous supply of grains is required.
Annually 1010 kilograms of grains are needed. That is 700 times more mass than humanity has put into space so far. If you feed this from earth, it will cost roughly 1018 joules of energy – 20,000 times the energy required to launch Saturn V. When launched from the moon, where the dust then drifts towards L1 via a natural path, ‘only’ 1017 joules required – 2,500 Saturn V launches. The required energy could be generated on the moon itself, the researchers suggest.
Mine on the moon
“I think it’s a nice piece of work, and it’s good that this is taken into account so that the research field grows,” says Jeannette Heiligers, assistant professor of astrodynamics & space missions at TU Delft. “A lot of assumptions always have to be made with these kinds of calculations. Here, for example, that you can create perfect particles, and that you have a mine available on the moon. In fact, you should be investigating such a technique with many more disciplines at the same time. Then it can be taken into account how feasible a mine on the moon really is in terms of required technology, time frame and costs. Climate scientists could therefore say more about seasonal application. That is now being mentioned, but the consequences are not elaborated.”
Based on the new publication, it is very difficult to say whether a dust cloud between the sun and the moon is better or worse than other geoengineering techniques, says Heiligers. “You have to be able to weigh up four criteria for this: effectiveness, safety, feasibility in terms of time, and costs. This research mainly says something about effectiveness.”