On behalf of Alan Robock:

There are actually many more issues with geoengineering. I have a list of 26 reasons why stratospheric aerosol geoengineering may be a bad idea, and you can read the paper at http://climate.envsci.rutgers.edu/pdf/StratosphericAerosolGeoengineering4.pdf

At the same time, we have to list all the potential benefits. Policy decisions will need more research so each of these can be quantified, but I agree that the governance issues will be insurmountable. Here are the lists:

Benefits (* = volcanic analog)
1. Reduce surface air temperatures*, which could reduce or reverse negative impacts of global warming, including floods, droughts, stronger storms, sea ice melting*, land-based ice sheet melting, and sea level rise*
2. Increase plant productivity*
3. Increase terrestrial CO2 sink*
4. Beautiful red and yellow sunsets*
5. Unexpected benefits

Risks
1. Drought in Africa and Asia*
2. Perturb ecology with more diffuse radiation*
3. Ozone depletion, with more UV at surface*
4. Whiter skies*
5. Less solar energy generation*
6. Degrade passive solar heating
7. Environmental impact of implementation
8. Rapid warming if stopped*
9. Cannot stop effects quickly
10. Human error
11. Unexpected consequences
12. Commercial control
13. Military use of technology
14. Conflicts with current treaties
15. Whose hand on the thermostat?
16. Degrade terrestrial optical astronomy*
17. Affect stargazing*
18. Affect satellite remote sensing*
19. Societal disruption, conflict between countries
20. Effects on airplanes flying in stratosphere*
21. Effects on electrical properties of atmosphere
22. More sunburn (from diffuse radiation)
23. Continued ocean acidification
24. Impacts on tropospheric chemistry
25. Moral hazard – the prospect of it working would reduce drive for mitigation
26. Moral authority – do we have the right to do this?

-Alan Robock

On behalf of Ken Caldeira:

Paul R. Ehrlich and Andrew Beattie raise some pertinent arguments but fail to address a central question: If there is a rational expectation that some solar geoengineering scheme would reduce harm and suffering caused by the greenhouse gas emissions of others, is it ethical for armchair ethicists to prevent a deployment of a solar geoengineering scheme and therefore inflict greater harm and suffering on others?

Are the authors opposed to learning more about solar geoengineering? Is ignorance in this case preferable to knowledge?

My main interest in exploring solar geoengineering schemes is the preservation of biodiversity. Solar geoengineering schemes may not be able to reduce overall climate risk and climate damage; however, if they don’t work, absent a radical cessation of greenhouse gas emissions, I see few other feasible paths to protecting delicate ecosystems (e.g., arctic ecosystems, coral reefs).

-Ken Caldeira

On behalf of Michael Huesemann:

It is disturbing that is has come to this: We have messed up the atmosphere with one set of technologies (i.e., fossil fuel burning machines and power plants) and then attempt to “fix” the problem with another set of bizarre geo-engineering technologies. As pointed out in “Technofix: Why Technology Won’t Save Us or the Environment”, foreword by Paul and Anne Ehrlich, (http://www.newtechnologyandsociety.org), techno-fixes such as geo-engineering won’t offer long-term satisfying solutions because they have unintended consequences that are inherently unpredictable by science and they don’t address root causes (i.e., fossil fuel burning), thereby delaying the implementation of lasting solutions.

The Kaya equation, which is similar to the I=PAT equation (P.R. Ehrlich and J.P. Holdren, “Impact of population growth”, Science, 171:1212-1217, 1971), can be used to analyze the root causes of CO2 emissions. CO2 emissions are the product of “population” (number of people or consumers) times “material affluence” (GDP per person or per capita GDP) times “carbon intensity of the economy” (tons of CO2 emitted per GPD generated).

We can reduce the carbon intensity by having more fuel efficient cars and power plants and by switching to renewable, carbon-neutral energy sources. However, the large-scale generation of renewable energy, on a scale needed to replace fossil fuels, is likely to also have negative environmental consequences.

We can stop the endless growth of material and carbon-intensive affluence by transitioning to a steady-state economy, as advocated by Herman Daly and others for decades. Unfortunately, mainstream economists still don’t get the message.

And we can reduce carbon emissions by reducing the number of consumers by having clear population policies, a subject that seems taboo despite Paul and Anne Ehrlich’s persistent effort to inform the public. According to an analysis by Paul Murtaugh and Michael Schlax (“Reproduction and the Carbon Legacies of Individuals”, Global Environmental Change, 19:14-20, 2009), avoiding the birth of a single child has a much a greater effect on reducing CO2 emissions than environmentally conscious consumer behavior. For example, it is estimated that an average citizen participating in personal conservation measures could reduce his/her lifetime carbon dioxide emissions by 486 tons, which is 20 times LESS than the CO2 emissions avoided by choosing to have one fewer child.

Clearly, there are more constructive ways for mitigating climate change than tinkering with geo-engineering, the ultimate techno-fix.

-Michael Huesemann

On behalf of Matt Herring:

Thanks Paul and Andrew. Clive Hamilton’s latest book – “Earth Masters, playing god with the climate” – covers these and other key geoengineering issues in penetrating and wide ranging detail. I highly recommend it.

-Matt Herring