1.2 Forms of geoengineering

One of the approaches most likely to be affordable is the deliberate pollution of the stratosphere with sulphate to reduce the amount of sunlight reaching the earth's surface. This would be cheap as it could be done by the addition of sulphur to jet fuel. We know it would work to slow down warming because it imitates a large volcanic eruption. (The earth was cooler for more than a year after the eruption of Mount Pinatubo because of the ejection of large quantities of particles.) But there are many possible negative consequences:

• ocean acidification continues or even increases

• acid rain

• possible negative health impacts

• other unintended consequences.

I personally feel we should do everything possible to avoid needing to resort to a strategy as potentially negative as this one.

Another geoengineering approach is to support the earth's natural cooling systems in the tropics, which are mainly mediated by low altitude clouds and cumulonimbus clouds. You can find information about this from the Global Warming Project website; in particular see their report, The Global Cooling Project, pages 1–20.

Since about 2007 there has been a lot of discussion about the use of biochar (charcoal generated through a chemical process) for storing carbon soil (or even for burial at sea) as a form of geoengineering. If you do a Google search you will find a range of opinions from strong opponents (e.g. Vandana Shiva) to strong proponents (e.g. Peter Read). Overall, it appears the jury is still out and that biochar has prematurely been over-promoted as a climate fix.

An article that is particularly strong on assessing the relative benefits of a range of geoengineering strategies, though it is not exhaustive, is by Lenton and Vaughan.