Geoengineering (or Geoengineering) is art (because it is more an art than a science at present) of trying to modify the climate, it is not necessarily a new science (see the report Arte above ) But it is becoming more and more important at the moment with the aim of limiting global warming ... with or without the support of the populations ...
Here are some techniques and techniques of Geo-Engineering that we analyzed and commented on in the subject How to cool the Earth?
1) Deviate solar radiation with a spatial "umbrella"
In my opinion, the most cranky of the proposed solutions is to send 20 millions of probes (if yes) filled with deflector at the Lagrange point at 1,5 Million km of Earth (or solar gravity = Earth's gravity).
Purpose: To reduce the solar flux of 1,8% by creating a permanent spot on the Earth of several thousand km.
Duration: 50 years ...
2) Deflect and absorb solar radiation by "smothering" the atmosphere
Somewhat the same process as the 1) but staying on Earth (thus already more reasonable) by spraying H2S in the upper atmosphere which would quickly transform into SO2 deviating thus the solar rays.
Purpose: to earn "some degree" on 10 years
ps: the H2S is deadly in high concentration. At low concentration it "stinks the egg". It happens that we feel it next to the de-sulfurization unit of the oil refinery ...
3) Raise the Gulf Stream
By 8000 autonomous seawater pumping platforms designed to "boost" the Gulf Stream in cold salt water at the right time of the year (thaw).
Purpose: add 1 million m3 to thermo-marine circulation
When we know the strengths and the thermal power of the Gulf Stream (thermal power equivalent to 1 millions of nuclear reactors) ... this solution seems very pitiful ...
4) Boosting the plankton sulfate Iron
The most "realistic" and probably effective solution that is to boost the plankton (and therefore the marine food chain) of some areas of the ocean that are deficient. The CO2 absorbed by the plankton is stored permanently in the sediments underwater of the corpses of their predator.
goal: to compensate 15% of our emissions CO2