9. Geo-engineering

Geo-engineering is a controversial approach to global warming which involves placing various substances into the atmosphere for the purpose of cooling the earth. The substances suggested are saline droplets, sulphur dioxide and calcium carbonate. Some have objected to this approach fearing that it will take the emphasis off the most important approach that of decreasing carbon emissions. However, given the limited success of this approach to date, solar engineering could serve as a stop-gap measure, giving the nations of the world more time to limit carbon emissions. The following are some of the current proposed experiments.

Stratospheric Controlled Perturbation Experiment (SCoPEx).
This is a proposed modest experiment consisting of putting small plumes of calcium carbonate into the stratosphere in a balloon release and the examining how the particles disperse. See The Sun Dimmers Nature 563:613-615, 2018. David Keith, one of the principal investigators, has set a goal of raising $20 million for the experiment. To date $12 million has been raised.

Marine Cloud Brightening Project
In this project US researchers propose to spray salt water droplets into the lower atmosphere to increase the reflectivity of the ocean clouds. This group has been attempting to raise funds for over a decade.

Use of Super Cool Coatings
A number of Super Cool Materials have been discovered that allow objects coated with them to remain 5 to 15 oC cooler than their surroundings (
1). They radiate the heat into space. A number of companies have been se up to commercialize these materials. The Comings Foundation will explore the use of these materials to increase the albedo of the earth.

If the world gets serious about geo-engineering there are a number of other sophisticated experiments that could be performed using high-flying aircraft to test this approach. It has been said that,
“Not talking about geo-engineering is the greatest mistake we can make right now.”

1. Super-cool Materials that Send Heat to Space.
Nature 577:18,2020.