Artificial cooling of the Earth through technologies that reduce incoming sunlight would not be enough to prevent extreme warming for long periods of time if it were not combined with a reduction in greenhouse gases, a new study confirms.
The study uses modeling to examine what would happen if hypothetically greenhouse gases were allowed to develop over the next century, while “solar geoengineering” was used to reduce global warming.
Solar geoengineering is a term used to describe a set of largely hypothetical technologies that would reflect sunlight far from Earth to reduce rising global temperatures and some of its associated impacts.
The most commonly proposed method for achieving this would be by releasing reflective particles, known as aerosols, into the stratosphere. Once released, the aerosols will form a protective shell around the Earth, scientists expect, reflecting incoming sunlight.
The idea has a natural analogue in volcanic eruptions, which in the past have temporarily cooled global temperatures. When a volcano erupts, it often sends a cloud of ash high into the atmosphere, which can lead to the production of aerosols that reflect far away sunlight.
Although in theory solar geoengineering could reduce the rise in temperature, it will not be able to deal directly with its root cause, which is the greenhouse gas emissions emitted by humans.
The new study, published in Notices of the National Academy of Sciences, found that hypothetically solar geoengineering would not be effective in reducing warming if greenhouse gases were allowed to rise to extremely high levels.
This is because extremely high levels of greenhouse gases in the atmosphere would cause low-lying clouds, known as stratocumulus clouds, to thin out and eventually disintegrate.
Stratocumulus clouds themselves cool the Earth, shading large parts of its surface from sunlight. If the straocomumlus clouds covering the subtropical oceans disintegrate completely, this could lead to an additional 5C global warming, the study said.
“Stratocumulus clouds are thinning at elevated concentrations of greenhouse gases and their exposure to sunlight is declining,” said study lead author Prof. Tapio Schneider, a climate scientist at the California Institute of Technology. The independent.
“Solar geoengineering may not be safe to prevent severe warming if it is extended for more than a century and greenhouse gas emissions continue to increase during this time.”
The study found that in simulations involving solar geoengineering, subtropical stratocumulus clouds decay when atmospheric carbon dioxide levels exceed 1,700 parts per million (ppm). This is more than four times the current level.
“I think the article provides another argument for why solar geoengineering cannot be a ‘no-jail’ card that frees us from the need to reduce our CO2 emissions; we can’t just burn all the fossil fuels in the ground and solve the problem of solar geoengineering, “said Dr. Doug McMartin, a senior fellow at Cornell University in New York who is not involved in the article. The independent.
“It’s just as important to emphasize that the scenario they’re looking at is really quite extreme.”
Carbon dioxide levels would reach just 1,700 ppm in the “super-extreme worst case”, where little is being done to tackle emissions after the 21st century, added Dr Pete Irvine, a professor of climate change at University College London. who also did not participate in the study.
So far, most research in the field of solar geoengineering has been done using computer simulations, which means that little is known about its potential effects on the real world.
In the future, however, a team of scientists from Harvard University plans to perform one of the first field tests for solar geoengineering.
The project, known as the Stratosphere Controlled Disturbance Experiment (SCoPEx), plans to use a high-altitude balloon to launch a package containing aerosols 20 km up into the stratosphere.
The amount of aerosols released will not be enough to have a cooling effect on the planet, researchers say, but it could allow scientists to collect data on how aerosol particles interact with air.
The scientists initially announced their intentions to carry out the experiment in 2017, but the project has so far been delayed by “technical problems”, according to the project’s blog.
Previous research has highlighted various social and ethical considerations related to solar geoengineering.
One is that if the technology is to be developed, it could be seen as a ‘quick fix’ to the climate crisis, with countries sticking to their commitments to reduce their greenhouse gas emissions. Another is that the technology can be misused by single actors or countries with malicious intent.
“The question of whether to do solar geoengineering is not purely scientific, but includes managerial, ethical and political issues,” said Prof. Schneider.