I also spoke briefly about the transcontinental movement of iron and fungi in the dust clouds from N. Africa, both of which cause problems in the Caribbean, killing coral, exacerbating red tides and causing asthma in children (18). Covering some of the dust producing areas in N. Africa could also reduce these problems.

Placing a white cover on the tundra or other surface adjacent to the Arctic Sea might have similar regional climate effects. If the ice in the Arctic Sea has a sensitivity to warming much greater than was thought (completely ice free in summer by 2020 instead of 2070-2100), then it might also be much more sensitive to cooling. Additional benefits would be refreezing of the permafrost, freezing or disappearance of Siberian meltwater lakes that are adding to the feedback going on and reduction of emissions of methane and CO2 from melting and dried out permafrost land.

I did want to mention that the University of Texas at Dallas has developed a carbon nanotube film and if such a material could be cost-effectively scaled up, it could replace the plastic film (19). This material is said to be super strong and lightweight (90lbs/square mile). Since 80% of the cost of the plastic cover project is the plastic, such a lower cost material could greatly improve its economic viability.

The producers also wanted me to talk about how a portfolio of geoengineering technologies could be simultaneously applied, since any one might have negative effects or other limitations that would make it unacceptable as a standalone approach.

I was going to say that the technologies should be prioritized based on how quickly they could be used and how effective they would be.

Plastic reflective ground covers, running jet engines rich to release soot or with high sulfur fuel or direct injection of sulfur dioxide gas can all be begun to some extent in less than 5 years. Ideas like the marine cloud generation project discussed on the program need to be shown they can work, so they need more than 10 years to be perfected and the space lens idea is a technology for the second, not first half of this century.

If the first four worked, then a combination of them could be used to offset all new forcing or some other significant percentage, all with the goal of delaying the warming for 50 years or however long until the renewable/carbon capture/hydrogen portfolio is in place.

The argument that we would have to continue with these treatments for hundreds of years until CO2 in ambient air is sufficiently reduced by natural processes and that alone is reason enough not to use them is fallacious for several reasons (20).

First, this assumes no advances in development and deployment of technologies that could remove atmospheric CO2. Although progress in this area has been very limited so far (21), one should expect some breakthroughs within 50 years.

Second, with these strategies we will eventually run up against a limit in terms of how much land can be covered and how much sulfur or soot can be injected before unacceptable side effects occur. The reason for using them in the first place is that there are no other choices, not because we want to use them to avoid having to reduce emissions. Thus, these are to be considered as temporary (50-100 years), but necessary delaying tactics, not permanent solutions that once adopted have to be continued in perpetuity because we want to or have to.

With the exception of the plastic cover, the implementation of these strategies has not been discussed in any detail. The discussion given in the NAS report from 1992 (22) is somewhat dated and not detailed enough and has been somewhat eclipsed by the recent papers by Crutzen (23) and Wigley (24, 25), which themselves are not implementation plans, but first attempts at discerning the important theoretical issues.

What I have presented below are not implementation plans either. Instead, I want to show how doable these options are and what must be considered if they are to be carried out. When I am done, you will see that these are not science fiction as these have been lumped together by the media with ideas that are, but large-scale engineering projects that can be undertaken within 5-10 years using existing technologies. It is the modeling and the understanding of impacts and effectiveness that is lacking, not the hardware or the technical know-how.