Geo-engineering refers to the deliberate manipulation of an environmental process that affects the earth’s climate, in an attempt to counteract the effects of global warming and climate change. It involves large-scale schemes for intervention in the oceans, lands and atmosphere. One type of project already underway in more than one location is the building of green walls across large swaths of the planet. These are made of indigenous vegetation and planted on the edge of deserts to stop the desertification of the surrounding area. The two biggest walls are the Three-North Shelter Forest Program in China, which is 4,500 kilometers long and aims to stop the spread of the Gobi Desert, and the Great Green Wall of Africa, which is 8,000 km long to curtail the Sahara. 

Climate change is being caused by the greenhouse effect – that is a buildup of carbon dioxide and other gases in the atmosphere – so there are two different kinds of geoengineering solutions: the first is to try to cool (down) the planet by reducing the amount of solar energy, while the second is to remove some of the atmospheric carbon dioxide.

Reducing Solar Radiation:

if Earth’s problem is that it’s receiving too much solar radiation, could the solution simply be to block out a fraction of the sunlight – just as we all do with sunscreens and sunblocks? Various schemes have been proposed. Firstly, volcanic eruptions can significantly reduce incoming solar radiation by firing sulfur dioxide gas into the atmosphere. Thus, pumping sulfur dioxide into the atmosphere should have a similar effect.
Another solution may entail orbiting kind of mirrors. But how realistic is it? Rough figures suggest we would need a mirror the size of Greenland!
Increasing Earth’s cloud cover represents a much more feasible solution, but geo-engineers wonder how long the clouds would last. Therefore, reducing solar radiation seems such a difficult challenge and we are still (far) from finding an effective measure to counteract (the issue).

Removing Carbon Dioxide

These proposals posit that it is possible to “suck” carbon out of the atmosphere on a massive scale, with several solutions ranging from carbon capture and storage (CCS) and “artificial trees” to ocean pipes and iron-seeding. CCS, also referred to as sequestration, is based on built in “scrubbers” which would trap the waste carbon dioxide gas and turn it into a highly compressed liquid that could be easily stored.
Regarding the ocean pipes, in 2007 climate scientist James Lovelock proposed a system of giant vertical pipes, in order to constantly add cold water into the oceans and stimulate algal growth, since it is biologically more productive than warm water.

The 2015 National Research Council report found present schemes unviable and risky to be pursued. Indeed, most of these proposals do not deal with CO2’s other major impact: ocean acidification. In addition, several environmentalists argue that geo-engineering is unethical and question the morality of tinkering with the planet’s climate.
In conclusion, since administering any such scheme would obviously raise issues of geopolitics and global governance, much more research is needed to achieve a globally shared solution.