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Photo Source: MIT if carbon emissions on the planet are getting out of control, how should we deal with the crisis of global warming? Scientists have come up with a possible strategy: directly change external conditions so that the earth receives less sunlight.

In recent years, do you feel like you've heard more and more reports of extreme weather: heat waves sweeping the world, abnormal precipitation and droughts, rampant wildfires and rising sea levels? Global warming has changed from an early warning to our reality, making the climate system more unstable and seriously endangering the survival of human beings and many other species. According to the current trend, can we mitigate or reverse climate change? It seems difficult for most people to give a positive answer. Scientists have come up with possible backup plans to avoid the worst outcome for mankind.

As the main cause of global warming, emissions of greenhouse gases such as carbon dioxide and methane are still on the rise. The sixth assessment report of the United Nations Intergovernmental Panel on Climate change (IPCC) shows that in order to achieve the Paris Agreement's goal of keeping the global average temperature rise below 1.5C, net zero carbon dioxide emissions will be achieved by the early 1950s, which requires immediate deep emission reduction measures in all areas, otherwise it will no longer be possible to achieve this goal. In fact, even under the most ideal circumstances, if mankind were to stop all greenhouse gas emissions from today, the earth's temperature would continue to rise because ocean currents would bring excess heat from the deep sea back to the surface. It will only gradually decline after it has stabilized over the next few decades. Therefore, at least in the near future, the task of solving global warming is arduous and urgent.

In the global warming bar chart from 1850 to 2021, the color of each bar corresponds to the global average temperature in a given year. The warmer the color, the higher the temperature, and the darker the color, the more extreme the temperature. The data are from the British Met Office. Image source: Ed Hawkins | University of Reading in order to solve this problem, geoengineering (geoengineering) came into being. In order to deal with human-induced climate change, geoengineering aims to use new technologies to carry out cautious and large-scale intervention in the natural system of the earth. Such technologies are generally divided into two main categories. The first is greenhouse gas elimination (GGR), which aims to remove greenhouse gases from the Earth's atmosphere, such as the use of biochar to solidify and store greenhouse gases, enhanced mineral weathering and afforestation. The other is solar radiation control (SRM), which is a bit bold and unexpected: if you can't limit carbon emissions, can you start directly from the source and reflect a small portion of the sunlight that hits the earth back into the universe?

In a paper published in 1989 in the magazine of the British Interstellar Society, James Early (James Early) proposed that lunar material be used to create an extremely thin glass barrier with a diameter of 2000 km and transport it to the first Lagrangian point (L1) about 1.5 million km from Earth. In this position, the gravitational forces of the sun and the earth cancel out, so the space barrier is more stable. The glass barrier conceived by Early can block about 1.8 per cent of solar radiation directed at the earth and is expected to completely offset greenhouse gases in the 21st century, reversing the crisis of global warming. On top of this, American astronomy and optical scientist Roger Angel (Roger Angel) proposed an improved scheme in 2006: to solve the problem of building and transporting giant barriers, many small spacecraft several meters wide could be connected to form large barriers. Each small spacecraft is equipped with an extremely thin transparent optical barrier to deflect sunlight. Through the use of electromagnetic acceleration and ion propulsion, the barrier assembled on Earth is transported to the first Lagrangian point and is expected to last up to 50 years.

Set up a space barrier between the earth and the sun to reduce the solar radiation that reaches the earth. Photo Source: MIT recently, based on these studies, an interdisciplinary team at the Massachusetts Institute of Technology (MIT) came up with a new idea-replacing small spacecraft with bubbles. Not only that, the inflating process takes place after entering outer space, and the formed bubbles will form a huge barrier. This greatly improves the feasibility of the space barrier. In the preliminary experiment, in order to simulate the extremely cold vacuum environment in outer space, the research team created a stable frozen bubble at 0.0028 atmospheric pressure and maintained it at a temperature of-50 °C. At present, scientists are studying possible ways of inflating, such as the formation of bubbles using silicon-based melting materials, graphene-reinforced ionic liquids or other low vapor pressure melting materials. By controlling inflation, the thickness of the bubble film is similar to the wavelength of sunlight (about 400-600 nm), which may become one of the film structures with the highest efficiency of refraction of solar radiation.

The team created a frozen bubble film in the MIT lab with a diameter of 20 millimeters. Photo: MIT the research team estimates that the size of such a bubble film when unfolded in space will be similar to that of Brazil. Because of its large area and thin thickness, it will be greatly affected by solar radiation pressure. Therefore, the best position of the bubble barrier will be closer to the sun than the first Lagrangian point, and the modified position is about 2.5 million kilometers from the earth.

An artistic picture of the bubble barrier from the earth's perspective. Image source: MIT at present, the space bubble is still a preliminary idea, there are still many places that need to be studied and simulated, such as its transportation mode, stability and maintenance mechanism in space, accurate radiation reflection model, and so on. If the scheme is found to be feasible after analysis, the research team will first test it on a lower track. Under the ideal situation that all technical problems can be solved, it can be put into practice in this century. According to Rogge Angel's preliminary estimates, the project would cost 0.5% of global GDP over 50 years, but the exact amount needs to be further calculated.

A schematic diagram of the space bubble barrier. Image source: MIT's previously common solar radiation control techniques are mostly used in the interior of the earth, such as increasing the reflectivity of clouds or the earth's surface, or dissolving small reflective particles (such as sulfate particles) into the troposphere or stratosphere. However, the latter met with strong opposition. Earlier this year, more than 60 international policy experts and scientists called on the government to stop such projects because it is likely to disrupt monsoon rains in some areas and fail to achieve extensive and effective control.

In contrast, the implementation of the bubble barrier scheme in outer space avoids further risks to the Earth's ecosystem. At the same time, one of the biggest advantages of this scheme is that it is completely reversible: simply by continuing to inflate, the force on the surface of the bubble exceeds the equilibrium point, and the bubble will burst. This approach also reduces the amount of garbage left in the universe after abandoning the barrier.

However, the earth's environment is complex, and like all solar radiation control technologies, the impact of the air bubble barrier on the earth's environment is still worrying. Some studies have shown that reduced solar radiation can cause climate effects such as weakening the trajectory of tropical storms, while cooling tropical areas may help the survival of the malaria parasite and increase the risk of malaria transmission. Because such technologies only balance the total amount of greenhouse gases and do not reduce carbon emissions, it cannot solve all the problems, such as ocean acidification caused by excessive carbon dioxide emissions. In addition, if such programs stop suddenly, there may be a "stop shock" (termination shock) phenomenon on the earth, leading to a rapid rise in the earth's temperature. In terms of public policy, how to cooperate with the emission reduction plan and the solar radiation control plan is also an issue that needs to be discussed. The space bubble program is not a substitute for human emission reduction measures, but a supplementary and backup plan. "We believe that if the need for geoengineering becomes urgent, further improving the feasibility of solar radiation barrier research will help us make more informed decisions in the future," said Carlo Ratti of the Massachusetts Institute of Technology.

In the face of serious environmental problems, protecting natural systems such as vegetation and oceans that absorb and store carbon and reducing carbon emissions from human activities are still the most important and fundamental solutions. From the transition from fossil fuels to clean energy, to choosing green travel methods in daily life and avoiding extravagance and waste, every country and field in the world is actively improving policies and developing new technologies in response to global warming. For each of us, we might as well be less negative and do what we can.

Reference website:

Https://www.ipcc.ch

Https://www.climate.gov/news-features/climate-qa/can-we-slow-or-even-reverse-global-warming

Https://www.gov.uk/government/publications/geo-engineering-research-the-government-s-view/uk-governments-view-on-greenhouse-gas-removal-technologies-and-solar-radiation-management

Https://www.homepages.ed.ac.uk/shs/Climatechange/Data%20sources/Early%20earth%20shield1989.pdf

Https://www.pnas.org/doi/abs/10.1073/pnas.0608163103

Https://senseable.mit.edu/space-bubbles/

Https://www.france24.com/en/live-news/20220117-dimming-sun-s-rays-should-be-off-limits-say-experts

Https://www.cdstm.cn/gallery/hycx/qyzx/202205/t20220516_1069178.html

Https://www.dropbox.com/sh/gk415yke8shtb84/AADfZbzC8xISX-lTmEkJJ7V2a?dl=0

Photo Source: http://showyourstripes.info/c/globe/

This article comes from the official account of Wechat: global Science (ID:huanqiukexue), written by | Meng Fanqiong revision | Wang Yu

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