SKY & SPACE
1. Stratospheric sulfate aerosols
It is preventing from sunlight by seeding small and reflective particles. this idea inspired by explosion of mountain pinatubo in 1991. After that, scientists have suggested artificial volcano as a solution. Seeding particle's size is much smaller than micrometer. If a particle is larger than that size, it can trap outgoing heat and have warming effect. And in that sense, sulfate particles are very good materials. Because sulfate is small and white, so it has high albedo. If we seed H2S or SO2 on stratosphere, they oxidize and remain sulfates. Then, Why stratosphere? Because stratosphere is very stable. If we seed them on troposphere, sulfate particles are disappeared right away. Besides, geo-engineers insist that sulfates can't be acid-rain. Because, the amount of seeding is much less than industry activities’. Also there is natural sulfate layer in the lower stratosphere, because stratosphere is stable. Experts say that spraying of 100 ~ 500 million t S/year is required to be effective. This is 1/10 level of emission by airplane. But because sulfate effect is short, we may continuously spray sulfates for decades or centuries. Tom Wigley of NCAR(US National Center for Atmospheric Research) claimed that Jet engine, balloons and etc. can contribute to reducing solar energy and minimizing sulfur pollution.
2. Space mirrors
It is proposed by Roger Angel with the purpose to reflect a percentage of solar sunlight into space, using mirrors orbiting around the Earth. How about interrupting sunlight before passing atmosphere? Installing deflection device in space started from 20 years ago. James Early at Lawrence Livermore National Laboratory, in 1989 proposed using a "space shade". Members at Livermore, suggested installing 55,000 of 100 m2 mirrors. We can get materials of space mirrors from moon or comet. If we make the mirror small and light, the cost will decrease, but the lifetime will be shorten. So point L1 is considered as installation site because L1 is where both earth and sun has same gravity. This location is very stable, so although mirror goes out of its orbit, it's recovered.
3. Cloud reflectivity enhancement
Cloud is good at interrupting sunlight. This idea is returning solar energy into space by making clouds. If the number of CCN(Cloud Condensation Nuclei) is increased, cloud albedo will be high and lifetime will be long. The smaller cloud particle, the more clouds reflect sunlight. Because surface area is large and floating period is long. To make clouds, the technique that seeds particles of appropriate size and precise amount is required. Now the technique is the level of laboratory, so we have to expand the scale. In 2008, John latham, UCAR(The University Corporation for Atmospheric Research), published in "If cloud amounts doubles than now, earth can bear doubled CO2" in Philosophical Transactions'. Especially important cloud is a stratus of low altitude over the coast. This cloud is dense and has high albedo, so it interrupt sunlight effectively. But high clouds absorb long wave radiation and warm atmosphere. Around equator, there are much high clouds. So we have to research about equator's clouds to prevent equator warming and block warming of equator and remain cooling effects of clouds.
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