Solar geoengineering to cool the planet
The last chance to stop global warming — or a delusion of grandeur? Scientists are working on innovative ways to artificially cool the planet. As the planet continues to get warmer, could geoengineering be our best shot at a solution? “There is no doubt that humans are able to artificially cool the planet,” explains David Keith from Harvard University. Keith is a researcher in solar engineering — a very controversial field. Mostly because it’s all about discovering if and how humans can manipulate solar radiation on Earth in order to slow down climate change. Here are different forms this idea could take — which may or may not work.
Mimic the power of volcanoes
When the Pinatubo volcano in the Philippines erupted on June 15, 1991, tons of ash and gas shot into the atmosphere and travelled for miles. It was the second-largest volcanic eruption of the century. To the surprise of many scientists, the event cooled the Earth by around half a degree Celsius in the months that followed. Tiny particles in the air called aerosols reflected more sunlight back into space compared to normal conditions. The result: reduced global warming.
Scientists like Keith want to artificially mimic this volcano effect. The theory behind it is known as stratospheric aerosol injection (SAI). It involves introducing sulfur aerosols into the stratosphere between 15 and 50 kilometers (9 and 31 miles) above the Earth’s surface. The aerosols would then, theoretically, combine with water particles and reflect more sunlight than usual for the next one to three years.
“There’s evidence from basically every single climate model that shows that if you do a pretty even north-to-south east-to-west distribution of aerosols in the stratosphere you can reduce many of the most important climate hazards,” says Keith. “So, changes in water availability, changes in temperatures, including extreme temperatures.”
In order to make it permanently cooler, the aerosols would need to be put into the stratosphere over decades and over a large area. Achieving this would require balloons, artillery, airplanes or even huge towers. But this seemingly simple solution also poses some considerable risks. Some scientists fear it could lead to an increase in extreme weather conditions, trigger acid rain or damage the ozone layer. Critics even view the technology as a potential climate weapon.
Use the sea as a mirror
It sounds unbelievable, but some scientists are researching how to cool the planet by covering large parts of the ocean with artificial foam. This process is also known as “ocean foaming” or “micro-bubbles.”
About 70% of the Earth’s surface is covered by ocean. The water — which is mostly dark due to its depth — reflects very little sunlight and stores a lot of heat. The lighter the surface is, the less it heats up. This is called the albedo effect. And it could also be harnessed on the water.
“The idea of micro-bubbles in the ocean is making a foam to reflect away some portion of incoming solar radiation and to deploy it in strategic locations where you could possibly effectuate certain climate outcomes,” explains Corey Gabriel, a climate scientist from the University of California San Diego.
In theory, this foam could reflect 10 times more sunlight than dark water surfaces. With enough foam, this should be able to cool the planet by 0.5 degrees Celsius. Some scientists have suggested that the foam could be stirred up with the help of specialised ships. Or container ships around the world could deploy it in different areas of the ocean. The method, however, remains largely unexplored and is far from being a viable solution. And the impact that huge amounts of sea foam could have on marine ecosystems is still unclear. Its potential impacts on the climate, as well as local weather events, would also be very difficult to control.