Tuesday, July 25, 2017

Climate Change and Geoengineering: Artificially Cooling Planet Earth by Thinning Cirrus Clouds

[Newsweek] As part of the Paris Agreement in 2015, nearly 200 world leaders agreed to curb greenhouse gas emissions and strive to keep temperatures at 1.5 degrees Celsius above pre-industrial levels in order to avoid dangerous and irreversible climate change by the end of the century.
At present, climate scientists regard warming of two degrees above pre-industrial levels as the threshold for global warming. After this point, extreme weather will become more likely—increasing the risks of storms, droughts and a rise in sea levels. Consequences include food and water scarcity, and increased migration as parts of the planet become uninhabitable.
If global emissions continue on their current trajectory, some scientists estimate we will surpass the two-degree limit by 2050. And with Donald Trump poised to pull the U.S. out of the Paris Agreement, the chance of achieving the set target looks even less likely.
Over recent decades, scientists from across the globe have been discussing the potential of geoengineering—the deliberate manipulation of the environment that could, in theory, cool the planet and help stabilize the climate.
There are main two types of geoengineering. The first involves removing carbon dioxide from the atmosphere and storing it. This is already being done on an industrial scale, but it is not effective enough at the moment to cope with the huge levels of emissions. The other type, solar radiation management, is more radical—an attempt to reduce the amount of sunlight absorbed by the planet by reflecting it away.
Many ways of doing this have been proposed. One of the most widely discussed (and riskiest) involves the injection of reflective aerosols into the upper atmosphere. This plan is based on the cooling effect of volcanoes: Sulfur dioxide emitted in an eruption causes the formation of droplets of sulfuric acid. These reflect the sunlight away, creating a cooling effect. But this plan could also go very wrong. The sulfuric acid could strip away the ozone layer, leaving Earth completely exposed to the sun’s radiation.
In an article published in the journal Science, Ulrike Lohmann and Blaž Gasparini, from the ETH Zurich, in Switzerland, discuss a variation of this idea: the thinning of cirrus clouds to target the long-wave radiation coming from Earth.
Cirrus clouds are thin and wispy clouds that form at high altitudes and do not reflect much solar radiation back into space, creating a greenhouse effect. The higher the altitude at which they form, the larger the warming effect on the climate. And in a warmer climate, cirrus clouds form at higher altitudes.
So what if we got rid of them? These clouds could be thinned out—leading to a reduction in their warming effect—by seeding them with aerosol particles like sulfuric or nitric acid, which act as “ice nucleating particles” or INPs. If these are injected into the level of the atmosphere where cirrus clouds form, the way they form would be altered, resulting in thinner clouds that have less of a warming effect. Read More