Scientists agree that we need to swiftly and dramatically cut emissions of heat-trapping gases. Also necessary: safely and sustainably removing carbon dioxide from the atmosphere, and accelerating investments to prepare for the impacts of climate change.
Solar geoengineering is the idea that we could slow global warming by increasing the amount of sunlight reflected back to space or by allowing more heat to escape Earth’s atmosphere.
Global warming is caused by a buildup of carbon dioxide and other greenhouse gases that trap heat from the Sun within Earth’s atmosphere. Reducing the amount of sunlight that reaches Earth, or allowing more heat to escape the atmosphere, could help to cool Earth’s surface.
Solar geoengineering, also known as solar radiation management, is a geoengineering technique that works by reflecting some sunlight away from the earth, lowering the amount of solar radiation that reaches earth's lower levels of atmosphere.
This would be done by releasing massive amounts of sulfur dioxide (SO2) into the atmosphere from across the globe. It would allow us to control the climate to a certain extent – by lowering the amount of ultraviolet radiation from the sun that hits earth surface, the sprayed SO2 would weaken the intensity of the greenhouse effect on earth and help to protect earth's natural systems and our climate system.
Logistically, this would happen by flying planes once or twice a year over the equator, spraying the SO2 aerosols into the atmosphere. What solar geoengineering research has going for itself is that we already have the planes and spraying technology available to implement this solution – so other geoengineering technologies wouldn't be necessary for this stratospheric aerosol injection.
There are several proposed solar geoengineering technologies. These include marine cloud brightening, cirrus cloud thinning, space-based techniques, and stratospheric aerosol scattering, amongst others.
Marine cloud brightening would attempt to brighten marine clouds to reflect more sunlight back into space.
Cirrus cloud thinning would attempt to reduce the thin, high-altitude cirrus clouds to emit more long-wave radiation from the earth to space.
Space-based technologies would attempt to reflect a small fraction of sunlight away from the earth by positioning sun shields in space.
Lastly, stratospheric aerosol scattering would introduce tiny reflective particles, such as sulfate aerosols or perhaps calcium carbonate, into the upper atmosphere, where they could scatter a small fraction of sunlight back into space.
Imagine a future where, despite efforts to reduce greenhouse gas emissions quickly, parts of the world have become unbearably hot. Some governments might decide to “geoengineer” the planet by spraying substances into the upper atmosphere to form fine reflective aerosols – a process known as stratospheric aerosol injection.
Theoretically, those tiny particles would reflect a little more sunlight back to space, dampening the effects of global warming. Some people envision it having the effect of a volcanic eruption, like Mount Pinatubo in 1991, which cooled the planet by about half a degree Celsius on average for many months. However, like that eruption, the effects could vary widely across the surface of the globe.
How quickly might you expect to notice your local temperatures falling? One year? Five years? Ten years?
What if your local temperatures seem to be going up?
As it turns out, that is exactly what could happen. While modeling studies show that stratospheric aerosol injection could stop global temperatures from increasing further, research shows that temperatures locally or regionally might continue to increase over the following few years. This insight is essential for the general public and policymakers to understand so that climate policies are evaluated fairly and interpreted based on the best available science.
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