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.
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
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
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
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