In response to Ken Caldeira's comments about ozone, it is indeed the anthropogenic chlorofluorocarbons that supply the chlorine that catalytically destroys ozone. Aerosol particles in the stratosphere, whether from polar stratospheric clouds, volcanoes, or geoengineering, facilitate the reactions that release this chlorine from stable compounds and allow it to destroy ozone. The World Health Organization finds, "Computational models predict that a 10 percent decrease in stratospheric ozone could cause an additional 300,000 non-melanoma and 4,500 melanoma skin cancers and between 1.6 and 1.75 million more cases of cataracts worldwide every year." Even if geoengineering depleted the ozone an additional 3 percent, as Pinatubo did, causing only one-third of these effects, should we deliberately take an action with these consequences?
As Ken points out, the effects of chlorine on ozone will diminish with time, but a recent Science report shows that geoengineering will extend the effects of chlorine on ozone depletion by 30-70 years. This effect as not inconsequential.
On a separate note, I'm not sure what Ken is saying about values, facts, and scientists as intellectuals. My values do not affect the conclusions of my science. For example, I do not change the output from my computer models based on my expectations for the results. But science is not devoid of values. For example, how does one decide what research to do or not to do in the first place? Certainly this involves value judgments. How does one communicate the results to policy makers? This also involves values.
As I've written before, society must consider the benefits and consequences of any geoengineering scheme before it is implemented. And the same judgment must be made about emissions of greenhouse gases and mitigation strategies. Ken agrees. But just this statement involves values. Are we talking about the benefits and consequences to individuals, to nations, to corporations, to all of humanity, or to all life on the planet? ExxonMobil considers only the benefits and consequences to its corporation, and thus their decision so far has been to fight any mitigation efforts that hurt its corporate profits. In my personal value system, it's the role of governments to consider the benefits and consequences to all of their citizens and not just to their corporations. The U.S. government has been failing us in this regard for the past eight years.
My personal values are that people all have a responsibility for all of the creatures on the planet--human and otherwise--and that national boundaries are artificial. The U.S. government, as the most powerful on the planet, should exemplify these values for the benefit of all Americans and all other people. But even if your values are different, there is reason to be concerned about others. If climate change produces international insecurity and mass migrations, if it affects the U.S. food supply, if it affects the availability of medicines in disappearing natural environments, then Americans are affected. Concern for sea level rise in Bangladesh, Asian monsoon rainfall, excess UV radiation in Tierra del Fuego, drought in Africa, or stronger typhoons in southeast Asia, for example, not only benefits those countries' inhabitants, but also benefits U.S. national security. (A number of reports, including one by the Center for Naval Analysis and the CIA and another published in the Bulletin [PDF] give further credence to the connection between climate change and security. Also, climate scientists were awarded the Nobel Peace Prize, for working on climate change as a peace and security issue.) In addition, at the G8 summit this week we see how, without U.S. leadership, other nations can only agree on weak, unenforceable mitigation goals.
A scientist's role includes providing information to policy makers about the effects of their policies, so that they can make informed decisions. As particularly well-informed citizens, it also includes pointing out when these policy decisions are not in the best public interest. While my values do not affect the conclusions of my science, they do affect my essays, such as the one in the Bulletin that started this roundtable.
Tom Wigley makes several uncalled for accusations about my motives. I agree with what he says about the science, and have said these things before. But he accuses me of being inconsistent by conducting a climate model experiment without mitigation while arguing for mitigation. Yet, in my first comment I agreed with Tom that "a new geoengineering research program," is needed. In contrast to the situation with ocean fertilization experiments discussed by Dan Whaley and Margaret Leinen, there have been no international regulations or discussions of the propriety of geoengineering, let alone agreed-on protocols.
The way science progresses, and the way climate modeling is often carried out, is to run a model with an exaggerated scenario to see if there is a significant response, and then to later carry out experiments with more refined scenarios. As Ken Caldeira did before starting with equilibrium experiments (using large solar radiation changes to emulate stratospheric aerosols) and then more recently looking at transient experiments, our first experiments asked the question as to whether stratospheric aerosols that persisted for 20 years would produce transient or permanent changes in precipitation patterns (the answer was permanent) and examined how rapid global warming would be upon cessation of geoengineering. We never claimed that these experiments were more or less "realistic" than others.
Tom's definition of "realistic" presupposes that the goal of geoengineering is to keep the climate constant at the present level. As I asked in my original essay, if climate could be controlled, how would nations agree on how to set the thermostat? Furthermore, this discussion might be very contentious between different nations. Until this issue is settled, it is rather presumptuous to label the scenarios Tilmes et al., Rasch et al., and I used as "extreme" and Tom's as "realistic."
While Tom's analysis of global precipitation changes may be true on a global basis, it is regional precipitation changes in sensitive areas that are of concern. We showed that even if we keep the climate constant with a combination of increased greenhouse gases and geoengineering, there will be regions of large precipitation reductions. Finally, I repeat that a range of mitigation and geoengineering scenarios need to be studied. Our group is doing that now and national and international research programs need to support many other studies, as I've recently advocated.
It is indeed a challenge to make policy recommendations that result in the desired policy changes. There are many reasons why mitigation is the correct response if we take into consideration the costs and benefits to society as a whole and not to special interests. There remain many reasons why geoengineering may still be a bad idea, even with mitigation. I agree that more analysis is needed before we can make the geoengineering decision, but it is clear that we need mitigation now.