As the world continues to commit to reduce greenhouse gas (GHG) emissions, with the objective of achieve net zero emissions by 2050, a growing number of researchers are studying other courses of action to avoid the most pernicious effects of global warming, in case the increasingly likely case occurs that current mitigation and adaptation efforts prove insufficient. While the latter are currently the only options we have to deal with the consequences of global warming, the idea that we might need a plan B wins out big. Plan A, decarbonization, is not working as we expected, so it would be convenient if, from the middle of this century, we were in a position to apply geoengineering techniques.
One of these techniques is solar Geoengineering, a general term that groups different approaches to increase the reflectivity of the Earth, in order to compensate for the effects of GHGs accumulated in the atmosphere. It is a field of study, incipient 20 years ago, but which is currently the subject of multiple research works followed with growing interest by various governments and institutions.
For example, in the US, the National Academies of Sciences, Engineering and Medicine They have recommended that their government invest $200 million over the next five years to further investigate the issue. In 2021, these institutions published a report in which they point out that given the urgency of the risks raised by a planet that heats up rapidly, The federal government, in addition to having a solid portfolio of mitigation and adaptation policies, should carry out, in coordination with other nations, solar geoengineering research.
Currently, in addition to the US, Solar geoengineering is the subject of research in Australia, China, Germany, India, Norway and Sweden. In order to protect the Great Barrier Reef, Australia is already carrying out physical experiments in the lower part of the atmosphere (Cloud Brightening Project), while Harvard University is working on its own experiment (Stratospheric Controlled Perturbation Experiment or SCoPEx).
The modality of solar geoengineering currently the most researched (of which the SCoPEx is a good example) is the injection of aerosols into the stratosphere, a mechanism that basically reproduces the effects of a volcanic eruption from the release of reflective particles that temporarily cool the planet. Scientists have long known that when a volcano erupts, it releases large amounts of sulfur dioxide into the stratosphere. The resulting sulfate aerosols can remain there for several years, creating a reflective veil on a global scale. For example, when Pinatubo in the Philippines erupted in 1991, injecting 10-20 million tons of sulfur 20-30 km high, it caused a drop of 0.5°C over a year.
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For their part, Australian scientists are conducting experiments “sea cloud seeding & rdquor ;. This technique is based on the fact that clouds located about 800 meters above the ocean surface can be highly reflective. The ocean absorbs about 95% of solar radiation, But when microscopic droplets of seawater are released into the air over the ocean as they evaporate, they leave nanometer-sized salt crystals behind that can stimulate the thickening of clouds and increase their reflective properties.
At this moment there is a great controversy about solar geoengineering, not only scientific, but also about its geopolitical and ethical implications. In any case, those who support his study put forward a solid argument: solar geoengineering should never be a substitute for reducing emissions or to try to adapt to a warmer environment; rather, it is a tool that, backed by a large research effort, could become an option for cooling the atmosphere if current efforts prove insufficient.