Creating a shield of moon dust around the Earth to help reverse the effects of climate change was recently investigated in the PLOS Climate journal.
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In 2015, the global community agreed to pursue efforts to limit average global temperature rise to less than 1.5 °C above pre-industrial levels. Experts agree that this limit would prevent some of the most catastrophic impacts of global climate change.
While many experts publicly champion initiatives designed to meet the 1.5 °C limit, some experts say that exceeding the limit is unavoidable given the carbon emissions already in the atmosphere, according to Scientific American.
Low-key acknowledgment of this reality has given credence to controversial proposals focused on engineering our way out of a global climate crisis. These “geoengineering” or “climate intervention” proposals generally fall into two categories: remove greenhouse gases from the atmosphere or reduce warming from the sun.
Although the technology for these proposals does not currently exist at the scales needed, and some proposals potentially carry significant adverse side effects, it does not stop them from being taken seriously.
In the new PLOS Climate report, the study authors argue that a solar shield could reduce the amount of solar radiation that reaches Earth without significant negative impacts on Earth.
They also argue that a solar shield would not block out a disruptive amount of sunlight and would only dim approximately 1 or 2 percent of annual solar radiation.
Smoke aerosols emitted by large wildfires have produced a rapid and substantial cooling effect. However, wildfires also release tons of carbon dioxide, and any positive climate impact of fires is difficult to calculate.
The Challenges of Putting Up a Solar Shield
The study authors outline the challenges of developing and installing a solar shield. The most practical approach based on existing literature, the authors say, is using a massive dust cloud that orbits between the Earth and the Sun.
One of the biggest challenges with this approach is getting a dust cloud to track Earth’s orbit. In addition to battling gravity, a dust cloud would have to withstand radiation pressure from the Sun.
The study team said establishing a cloud inside the LaGrange point ‘L1’ would allow it to track our planet on an Earth-synchronous orbit. LaGrange points are points relative to the Earth and Sun where the gravitation forces of the two bodies cancel each other out to allow for a stable orbit.
This orbit would allow the dust cloud to resist the gravitational pull of the Sun and the Earth and the physical force of the Sun’s radiation.
The study team then assessed the various shadows that would be created by different types of dust cloud. In addition to blocking out radiation, the dust must be made of highly refractive material to resist radiation pressure from the sun. When an object deflects radiation rather than absorbs it, the pressure of photons is minimized.
The biggest challenge is creating a large enough cloud to have the desired impact on climate.
The study team found that about 109 kg of material would be needed, approximately one hundred times the greatest mass ever sent into space.
Grinding the dust into sub-micron grains would increase the surface area of a cloud, but it would also reduce the amount of shielding it would provide. Regardless of grain size, the cloud must be periodically replenished because the dust would drift out of alignment over time.
The Future of Building a Solar Shield
Ultimately, the study team concluded that the most practical approach would be to mine the fluffy dust covering the Moon’s surface, called regolith.
Moon dust could feasibly be launched along a solar orbit within the L1 point. With this approach, every photon deflected or absorbed by the dust cloud would have been earthbound. If the cloud were launched farther or closer, this efficiency would decrease.
Because the biggest, most reflective dust cloud will not have much of an impact if it does not last very long, the study team determined that launching it from the L1 point at speeds of around 10 meters per second would help the cloud to resist the effects of solar radiation.
At this point, the development is very much in the theoretical stage, and it is unclear if the study team's proposal would be effective or have unintended consequences. The study published in the PLOS Climate journal opens the door to further scientific inquiry and discourse, stimulating innovative thinking and collaborative efforts to confront the global climate crisis.
While a lunar-solar shield may hold promise, the path ahead demands meticulous study and deliberation to ensure sound decision-making and responsible stewardship of our planet's future.
References and Further Reading
Keller, J. K., & Eshel, G. (2023). Climate mitigation to avoid catastrophic warming is feasible but requires early and sustained action. PLOS Climate, 2(1), e0000133. https://doi.org/10.1371/journal.pclm.0000133
McGraw, P. (2023). The world will likely miss 1.5 degrees C. Why isn't anyone saying so? Scientific American. https://www.scientificamerican.com/article/the-world-will-likely-miss-1-5-degrees-c-why-isnt-anyone-saying-so
National Geographic Society. (2021). How extreme fire weather can cool the planet. National Geographic. https://www.nationalgeographic.com/environment/article/how-extreme-fire-weather-can-cool-the-planet?loggedin=true&rnd=1684259628448
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