To keep the planet's temperature down, one idea is to create an upper layer of the atmosphere using aerosols that reflect some of the sun's energy into space.All About Space (Image credit to Future) This article was brought to you by All About Space.All About Space magazine takes readers on an amazing journey through the solar system and beyond. It covers everything from the incredible technology and spacecraft that allow humanity to go into orbit to the complexity of space science.According to the U.K. Met Office, the Earth hit a grim milestone in 2021. The atmospheric concentration of carbon dioxide (CO2) reached 150% of its preindustrial value. The world must reduce its net carbon dioxide emissions to zero by 2050 to prevent the worst effects from climate change.Even if we could achieve this goal, it would not stop the rise in temperature. It takes time to see the impact of CO2 reductions on global temperature; the negative effects of global warming will continue for many decades. Is there any other way to reduce temperature rise faster?Harvard University researchers believe it is possible to temporarily reduce global temperatures by changing the composition of Earth’s upper atmosphere. In what they call the Stratospheric Controlled Perturbation Experiment, (SCoPEx), researchers were hoping to prove their theory and some of the technology. The team still hopes that the experiment will continue, even though the work has been halted.The sun is the ultimate source of Earth’s heat. It bathes the planet's daytime side in an infrared radiation stream that provides constant heat. The atmosphere reflects about 30% of this heat back into space, while the rest heats the planet at night and radiates back into space. Preindustrial times saw a delicate balance where the incoming heat was offset by the heat lost to space. This ensured that the average global temperature remained constant.Problem is that CO2 emissions are causing a disruption in this balance. They absorb some heat and trap it inside the atmosphere. The temperature rises more if there is more carbon dioxide in the atmosphere. To prevent climate change's worst effects, humans must decrease the amount of carbon dioxide in our atmosphere over the long-term. However, there are other ways to reduce global temperature.For example, volcanic eruptions can cause dust clouds to rise high into the stratosphere. This layer is the uppermost layer of the atmosphere and acts as a shield against some sun's heat reaching Earth's surface. For example, the Northern Hemisphere's average temperature dropped by approximately 1 degree Fahrenheit (more that half a degree Celsius) during the 1991 eruption of Mount Pinatubo. This was due to the fact that the volcano in the Philippines, Mount Pinatubo, erupted in 1991. SCoPEx wants to learn from such eruptions and inject particles into the upper atmosphere to lower temperatures.Simple idea of stratospheric Aerosol Injection, also known as SAI. At altitudes up to 12.4 miles (20 km), a high-flying aircraft, or helium balloon, would release aerosols in the stratosphere. This is much higher than what planes normally fly. The aerosols, which are too small to be seen from the ground as clouds but large enough to reflect some of the sun's energy into space, would remain suspended in air.Simulations show that SAI is a feasible concept. According to a 2018 report by the Intergovernmental Panel on Climate Change (IPCC), a fleet high-flying planes could release enough aerosols in order to offset current levels. However, the aerosols must be replenished every few year and only address one aspect of climate change, the greenhouse effect. It's best described as a temporary solution to rising temperatures and countries simultaneously reducing carbon dioxide levels.The research into SAI so far has been purely theoretical. However, there is limited real-world data available from volcanic eruptions. SCoPEx hopes to take real-world measurements in controlled conditions that will allow for better calibration of computer models. Frank Keutsch (principal investigator in the Department of Chemistry and Chemical Biology, Harvard University) said to the Boston Globe that ground-truthing models is necessary if we want to give decision-makers useful information about whether it could work.Most sulfur-based compounds are emitted by volcanoes. These compounds not only cool down the atmosphere, but also cause damage to Earth's protective layer of ozone which protects us from UV radiation. The SCoPEx team is now focusing on calcium carbonate chalk dust, which, in other words, researchers hope will have the desired cooling effect but not harm the ozone layer.Proposed experimentThe team would like to deploy a large uncrewed helium ballon that is similar to a weather balloon, but with propellers so that the ground team can maneuver it in controlled manner. Scientists were able to launch the balloon with the help of the Swedish Space Corporation.The balloon will not release any material into the stratosphere on its first flight, which is planned for next year. It would instead ascend to 12.4 miles. Here, the team would test its maneuvering system, and verify that all scientific instruments work correctly.A second flight of controlled calcium carbonate release would be performed at the same altitude if the test run was successful. The balloon would move in a straight line throughout the release. This would create a narrow plume of aerosol particles that measures 0.6 miles (1km) in length. According to SCoPEx, the balloon would then return through the plume and observe how the particles scatter over time and how much they reflect sunlight.The SCoPEx test flight was valuable for our understanding of SAI. However, it is important to keep the project in perspective. David Keith, a Harvard professor of Applied Physics, stated that the goal of the project is not to alter the climate or to see if sunlight can be reflected. "The goal is to improve our models of how aerosols form within the stratosphere."Keith stated that it will take at least a decade to complete large-scale aerosol releases. He said that the release could involve injecting 1.5 million tons [1.4million metric tons] of aerosol into the stratosphere each year. "Roughly 100 aircraft would be required to fly payloads at 12 miles [20km] altitude."The controversyHowever, SAI is still controversial. One concern is that humans caused the climate crisis by putting greenhouse gases into the atmosphere. So how can we be certain that aerosols will help? While computer modeling indicates that SAI is safe there are still risks. It could cause disruptions in weather patterns and crop damage by decreasing the amount of sunlight that crops receive. If sulfide aerosols were used, they can also harm the ozone layer.Some scientists are even wary about following the SAI route.Douglas MacMartin, a senior researcher associate and senior lecturer on mechanical and aerospace engineering at Cornell University, and a research assistant in computing and mathematical sciences, said that "that we might actually attempt to control the whole climate is a pretty frightening idea." In a 2018 discussion on what the IPCC called solar radiation modification (SRM), the panel concluded that the combined uncertainties of technological maturity, physical understanding, and the challenges of governance limit the ability to implement SRM in near future.These concerns led to the SCoPEx team postponing their maiden voyage of the helium balloon "until a more thorough social engagement process can be conducted in order to address issues related solar geoengineering research, Sweden"Keith said that there is a real danger in some organizations applying SAI without the scientific data SCoPEX needs. Second, SAI research will be criticized by corporations and governments that refuse to reduce carbon dioxide emissions.This could make it impossible to reap the potential benefits of SAI. Lizzie Burns is the managing director of Harvard’s Solar Geoengineering Research Program. She said, "It's kinda like a painkiller." It doesn't necessarily mean that you don't need surgery if you are taking pain medication.
