Scientists have long studied and debated the promises and perils of deliberately influencing Earth's weather and climate systems. But today, faced with ever more pessimistic predictions about the pace of global warming and the irrevocable damage it could do to the planet, some are talking seriously about implementing theoretical geoengineering schemes such as blocking the sun as an emergency response. In "20 Reasons Why Geoengineering May Be a Bad Idea" (May/June 2008 Bulletin), Alan Robock raises a host of scientific, social, and ethical issues posed by geoengineering. Below, Robock and his four fellow discussants debate how to weigh geoengineering’s potential benefits against its negative consequences.
The greatest danger that humans pose to Earth isn't geoengineering, ozone depletion, or even global warming. Rather, it's the climatic consequences of nuclear war. As recent work by Brian Toon, Gera Stenchikov, Luke Oman, Rich Turco, Chuck Bardeen, and myself has shown, we now understand that the atmospheric effects of a nuclear war would last for at least a decade--more than proving the nuclear winter theory of the 1980s correct. By our calculations, a regional nuclear war between India and Pakistan using less than 0.3 percent of the current global arsenal would produce climate change unprecedented in recorded human history and global ozone depletion equal in size to the current hole in the ozone, only spread out globally. We need to solve this problem so that we have the luxury of worrying about global warming and the consequences of geoengineering.
Still, geoengineering research needs to be federally funded at a robust level in addition to funding for research on nuclear winter and for mitigating global warming. It needs to investigate the efficacy, costs, and positive and negative effects of all proposed geoengineering schemes and should be based on an agreed set of scenarios for all researchers to use--as was done with the Intergovernmental Panel on Climate Change--so that results can be compared.
These scenarios need to include business-as-usual or mitigation scenarios for greenhouse gas and tropospheric aerosol emissions, combined with gradual and instantaneous aerosol injections into the stratosphere. We'll only be able to decide which scenarios are "realistic" after far more research on whether it's even possible to execute them, and what the climate responses will be. In the meantime, without a large injection of research support, we'll have to learn from ongoing efforts, which will produce results slowly.
As I reported in my recent Science article, an Energy Department white paper entitled "Response Options to Limit Rapid or Severe Climate Change"--prepared for President George W. Bush's National Climate Change Technology Initiative in October 2001--recommended $13 million per year be directed toward a national geoengineering research effort, but the paper was never released. I suspect that's because it would've been tantamount to the Bush administration admitting that global warming is a real problem.
As I wrote in Science, "It is not too late to make up for lost time, but we must avoid further delay. A research program, more generously funded than the one proposed in 2001, supported by the federal government with international cooperation, will allow us to compare the efficacy, costs, and consequences of the various options of responding to global warming, mitigation, sequestration, geoengineering, or doing nothing, so that an informed public can agree on the best courses of action."
This discussion began with Alan Robock's list of 20 arguments against geoengineering, so it's fitting to end with some comments on his most recent, more subtle contributions to this debate. Quite correctly, he asserts that his "values do not affect the conclusions of [his] science." This is the case for all good scientists. But he also points out that values may influence "what research [we] do or not do in the first place."
For many scientists involved in environmental research--and in research on global warming in particular--our concern for humanity's well-being at least partly motivates our quest to understand a complex problem so that we may respond to it effectively and efficiently. But there's another step, which, to avoid possible misinterpretation, I pose as a question: Within our fields of study, is it possible that values might influence the specific experiments we perform?
Alan claims that I have made "several uncalled for accusations" about his motives. This is manifestly wrong. In this roundtable I have not said anything about anyone's motives. I did, however, point out that there's some inconsistency between Alan's model study, in which he ignores mitigation, and his strong support for mitigation. I have urged from the start that geoengineering should only be considered as a supplement to mitigation. In that context, I believe that studies such as those by Alan, Philip Rasch, and Simone Tilmes that consider geoengineering alone are in danger of being misrepresented or misinterpreted. They greatly overstate the possible climate and stratospheric ozone side effects that might arise in a joint mitigation-geoengineering scenario.
It's undeniable that in a joint mitigation-geoengineering framework, these studies are extreme. They drive the climate-atmospheric chemistry system with a stratospheric aerosol loading far greater than would be necessary if we consider geoengineering and mitigation together--i.e., if we see geoengineering solely as a way to gain time to develop and implement the carbon-neutral technologies that are required to avoid dangerous changes in the climate, sea level, and ocean chemistry. This is what I consider to be a realistic option for the future, perhaps the only realistic option. Contrary to Alan's claim, I don't define "realistic" as a scenario that "keep(s) the climate at the present level."
As Ken Caldeira writes, "Prudence demands that we consider what we might do if cuts in carbon dioxide emissions prove too little or too late to avoid unacceptable climate damage."
If mitigation fails, either because we've underestimated the sensitivity of the climate system and/or because we've underestimated the technological and/or political challenges of reducing greenhouse-gas emissions, then we'll probably have to resort to some form of geoengineering. Clearly, this will then be a case where both mitigation and geoengineering are operating in tandem to avoid dangerous environmental change. This is what I see as a realistic scenario. We still have much to learn.
The widespread desire for the "good life" afforded by economic growth and development places us increasingly at risk of profound and widespread climate damage. Much of the developing world seeks to emulate the coal-powered development of China and India, while those of us in the developed world seek ways to kick-start our relatively moribund, fossil-fueled economies.
We need a climate engineering research and development plan. We may hope or even expect that we will collectively agree to delay some of this economic growth and development and invest instead in costlier energy systems that don't threaten Earth's climate. Nevertheless, prudence demands that we consider what we might do if cuts in carbon dioxide emissions prove too little or too late to avoid unacceptable climate damage.
A climate engineering research plan should be built around important questions rather than preconceived answers. It should anticipate and embrace innovation and recognize that a portfolio of divergent but defensible paths is most likely to reveal a successful path forward; we should be wary of assuming that we've already thought of the most promising approaches or the most important unintended consequences.
A climate engineering research plan must include both scientific and engineering components. Science is needed to address critical questions, among them: How effective would various climate engineering proposals be at achieving their climate goals? What unintended outcomes might result? How might these unintended outcomes affect both human and natural systems?
Engineering is needed both to build deployable systems and to keep the science focused on what's technically feasible.
Initially, emphasis should be placed on science over engineering. But if the science continues to indicate that climate engineering has the potential to diminish climate risk, increasing emphasis should be placed on building the systems and field-testing them so they'll be ready as an option.
There's a slippery slope from laboratory research to large-scale deployment. The science needs to start in computers and in the laboratory, but at some point, will need to proceed outside. It's only by experiments in the environment that we'll be able to test whether the models and laboratory extrapolations are relevant to the real world. And once experimentation starts in the outdoors, there's merely a matter of degree between experimentation and deployment.
Public engagement will be crucial, as will the framing of climate engineering research against the broader range of efforts to reduce both damage and risk of damage from climate change.
Because there are important societal decisions to be made regarding climate engineering, open public communication is necessary at all stages of research--closed scientific meetings on climate engineering must become a thing of the past. Climate engineering research programs should be internationalized and scientific discussion and results shared openly by all.
We cannot afford a new period of Lysenkoism and allow political correctness to pollute our scientific judgment. Scientific research and engineering development should be divorced from moral posturing and policy prescription. As scientists and engineers, we can say what is and what can be. Armed with this information, we can join with our fellow citizens to discuss what ought to be done.
Only fools find joy in the prospect of climate engineering. It's also foolish to think that risk of significant climate damage can be denied or wished away. Perhaps we can depend on the transcendent human capacity for self-sacrifice when faced with unprecedented, shared, long-term risk, and therefore can depend on future reductions in greenhouse gas emissions. But just in case, we'd better have a plan.
All of the participants in this roundtable have agreed that geoengineering research is necessary--although not all of us agree on whether experimental research in the open environment is necessary (or a good idea) in addition to theoretical research, modeling, and laboratory research. No less than the Intergovernmental Panel on Climate Change Fourth Assessment Report and the national academies of science of the G-8 countries have called for research into geoengineering. So how can the scientific community come to consensus about geoengineering research and make recommendations to governments for funding?
Geoengineering is a multidisciplinary activity, regardless of what strategy is being contemplated--solar radiation management, carbon dioxide drawdown by ocean iron fertilization, or any of the other suggestions that have been made. This means that no single scientific community can pose all of the research questions. Geoengineering options also inherently affect all nations through their impact on the planetary environment.
Appropriate scientific groups already exist that are well-suited to discuss research needs for geoengineering while considering how geoengineering interacts with economic, social, and governmental concerns. These research programs don't fund research, but provide a framework and mechanism for international scientific research priority-setting. Each could bring important intellectual resources to bear on understanding the way forward with geoengineering research:
These international global environmental change programs have taken notice of the active debate about geoengineering and have begun to discuss the role that they could play in identifying the research necessary to advance knowledge. For example, SOLAS undertook a review of ocean iron fertilization science, inspiring suggestions for the specific research necessary to understand the role that this technique could play in removing carbon dioxide from the atmosphere. (See "Mesoscale Iron Enrichment Experiments 1993-2005: Synthesis and Future Directions.")
These established programs, which influence research programs in individual countries, can play a convening role in bringing together scientists from around the world to consider research questions and the best ways to answer them. They can provide a forum for the development of international research priorities. They can sponsor research syntheses. And by virtue of their established communication pathways, they can link physical climate, biogeochemistry, biodiversity, and human elements of the complex landscape of geoengineering.
We urge the programs to consider the critical role that they could play in assisting the world's research communities in defining the path for future research.
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.
Alan Robock continues to misrepresent geoengineering using stratospheric aerosols. On one hand, he agrees that "it must be geoengineering plus mitigation, and never geoengineering instead of mitigation"; but on the other hand, he has run a climate model experiment that's precisely "geoengineering instead of mitigation." While his work identifies possible risks associated with the "instead of" idea, these risks cannot be transferred to the realistic "plus mitigation" case. It's a bit like pointing out the risks of skydiving without a parachute and saying they apply to the more sensible "with parachute" case. The same problem applies to the work on stratospheric ozone by Simone Tilmes and her colleagues.
Yes, it's useful to show that "geoengineering instead of mitigation" isn't a good idea. But we already knew that. What alarms me is that these studies strongly mislead unless given suitable caveats, as inexpert readers may think that the risks identified by these idealized sensitivity studies apply equally to realistic "geoengineering plus mitigation” scenarios.
From the start, I've advocated for the need to consider geoengineering in conjunction with mitigation as the only tenable option. Nevertheless, the implications of my work haven't sunk in, so I'll take this opportunity to explain them further.
I consider two cases: (1) a standard monotonic pathway to carbon-dioxide concentration stabilization at 450 parts per million (ppm)--the WRE450 case from my 1996 Nature article; and (2) an overshoot pathway where concentrations rise to 540 ppm in 2090 before declining to eventual stabilization at 450 ppm. The overshoot case gives us more time to reverse our emissions trajectory, which would be less costly and more technically feasible than a monotonic trajectory that requires stringent mitigation policies such as an immediate moratorium on building coal power plants.
So where does geoengineering come in? If we need extra time to stabilize atmospheric carbon dioxide at 450 ppm but don't want to risk a dangerous rise in temperature by overshooting it, then geoengineering could provide a negative radiative forcing equal to the difference that would occur between the monotonic and overshoot pathways. It's a trivial exercise to calculate this negative forcing--it would rise slowly from zero to peak at around -1 watt per square meter (the equivalent of turning off a Christmas tree light over every square meter of Earth's surface) in 2090 and then decline slowly back to zero.
The extreme cases considered by Alan, Tilmes, and their colleagues show that the negative climate and ozone consequences of geoengineering in the 450 ppm stabilization mitigation-plus-geoengineering scenario would be negligible.
For stratospheric ozone, the aerosol loadings for much of this century in the 450-ppm case would be about an order of magnitude less than those considered by Tilmes. By the time aerosol loadings reached an appreciable amount, the ozone layer would have essentially healed.
As for precipitation, the consequences of geoengineering would actually be beneficial. Alan brings up the issue that precipitation is more sensitive to short-wave (stratospheric aerosol) forcing than to long-wave (greenhouse gas) forcing. Thus, if one were to try to offset a large carbon-dioxide forcing with geoengineering, the positive precipitation increases due to enhanced carbon dioxide would be more than fully compensated and the net effect would be a (possibly detrimental) precipitation decrease.
But let's look at a realistic case. Suppose we follow a monotonic pathway to atmospheric carbon-dioxide stabilization at 450 ppm. Globally, this would lead to a precipitation increase relative to today of, say, X percent. The overshoot pathway would lead to still greater precipitation increases, say (X+Y) percent. Geoengineering to compensate for additional warming in the overshoot case would reduce precipitation by Z percent, where Z is greater than Y. The net effect of overshoot-plus-geoengineering would therefore be to increase precipitation relative to today by W percent, where W=X+Y-Z. W must be less than X. In other words, the combined scenario would lead to future precipitation that's actually closer to today than in the mitigation-only case. The differential short-wave/long-wave effect on precipitation actually works in our favor, contrary to what might be inferred from Alan's work and claims.
He sees the possibility that "the promise of geoengineering will delay the implementation of mitigation" as a primary danger. I disagree. As scientists who communicate with policy makers and politicians, the challenge is to ensure that this doesn't happen. Presenting scary extreme scenarios as relevant to the future isn't going to advance the mitigation cause. Indeed, crying wolf may well damage our credibility. Our responsibility is to explain why geoengineering can only be a complement to mitigation and evaluate the implications, costs, and technological challenges of scenarios that combine geoengineering and mitigation.
It's time to move on and assess the combined mitigation/geoengineering option in detail.
All geoengineering techniques raise some common (and complicated) questions: Should legitimate research activities continue? Should experimental as well as theoretical research take place? Who decides whether an experiment or project can go forward? Are people concerned about geoengineering because they fear that the research might be harmful, or because they're worried that the knowledge gained might be dangerous? Are science and business mutually exclusive activities?
Over the past month, a variety of bodies have gathered to discuss geoengineering techniques in an effort to better understand them--and perhaps better control their research and/or practice as well:
In addition to these meetings, last week, the academies of science for the Group of 8 Plus Five countries released a joint statement calling for additional geoengineering research. Secretary of Foreign Affairs of the U.S. National Academy of Science Michael Clegg interpreted their statement to include "approaches to soaking up carbon dioxide," specifically "the so-called fertilization of the oceans with iron."
Of this recent activity, we believe that the London Convention's proceedings provide a good model of how discussions between governments, scientists, and nongovernmental organizations may evolve. When the Scientific Group met in Ecuador, they formed an ad hoc working group on ocean iron fertilization to provide technical expertise in support of decision-making. The working group called on several oceanographers, including some that had participated in ocean iron fertilization experiments, for assistance in understanding technical issues.
Several external scientific groups also developed statements to inform these deliberations, including the Scientific Committee on Ocean Research; its U.N.-commissioned Joint Group of Experts on Scientific Aspects of Marine Pollution; and the International Oceanographic Commission (IOC). The academic research community also addressed questions of interest to the delegates in a Science magazine policy forum.
Although private companies and individuals cannot be parties to these agreements and cannot directly participate in meetings, parties to the London Convention provide opportunities for private concerns to inform its members through side sessions. Our company, Climos, made technical presentations during side sessions at the London Convention meeting last fall as well as at the most recent Scientific Group meeting.
The delegates reviewed a variety of scientific questions--ranging from whether large-scale experiments are justified scientifically (the consensus of the position papers from scientists was that they were) to whether ocean iron fertilization was harmful to the marine environment. (The consensus of the position papers was that there's insufficient scientific evidence to determine whether ocean-fertilization activities would pose any significant risks of harm to the marine environment.)
The Scientific Group will release its report on these discussions before the fall meeting of the parties in London this October, which will consider policy statements based on the input from the Scientific Group. The London Convention's legal consultants will also provide information on the legal basis for considering whether ocean iron fertilization is "dumping" under the technical definition of this activity within the London Convention.
On the other hand, the Convention on Biological Diversity adopted, with little deliberation or input from the scientific community and no input from knowledgeable private-sector stakeholders, a decision that expresses concerns about ocean iron fertilization and requests that governments ensure that activities don't take place "until there is an adequate scientific basis on which to justify such activities." But the IOC's ad hoc working group on ocean iron fertilization, of which Ken Caldeira is chair, recently released a response to that statement, saying that it "places unnecessary and undue restriction on legitimate scientific activities." The IOC will meet in Paris next week and will review the progress of the London Convention towards a scientific and policy framework for ocean iron fertilization.
We believe that the deliberative, science-based proceedings of the London Convention may serve as a useful model by which other international groups might consider proposals for adding aerosols to the stratosphere and other geoengineering activities.
Alan Robock suggests that I must respond to the "totality" of his argument--that it's not enough to pick off his 20 theses one-by-one, as if the "totality" of his position is somehow more than the sum of its parts.
For example, he repeats the canard that “geoengineering won't stop ocean acidification." The list of things that climate engineering won't do is endless. Reducing non-carbon greenhouse gases and black carbon soot also won't stop ocean acidification, but that shouldn't stop us from reducing them. Carbon emissions and climate engineering are two different things. Let's fault carbon emissions for what they do and fault climate engineering for what it may do.
In my earlier post, I wrote: "The Mount Pinatubo eruption lofted more than enough aerosols into the atmosphere to compensate for a doubling of atmospheric carbon dioxide, yet ozone concentrations fell by only 3 percent. And it's believed that this small reduction was caused by chlorine from human-made chlorofluorocarbons, which are now banned by the Montreal Protocol. So while the threat to the ozone layer is worth studying in greater detail, it's expected to diminish with time." Alan says that I'm wrong. But where exactly? Do we expect climate engineering at this level to destroy on average more than 3 percent of the ozone? Did chlorine not play an important role? Does the threat of ozone destruction increase with time?
Alan also asks us to agree "that if geoengineering is ever implemented, it must be geoengineering plus mitigation, and never geoengineering instead of mitigation." But what if we fail to enact effective mitigation? And what if there was substantial death and suffering as a consequence, and we thought the suffering could be alleviated, at least in part, by climate engineering? Shouldn't we then pursue it without mitigation?
While I'm in emotional agreement with Alan's statement, the rational side of me doesn't think it makes much sense. Some things sound nice, but may not be particularly reasonable when fully considered intellectually. Isn't the point that we wouldn't want to deploy climate engineering systems unless the benefits clearly outweigh the risks, where those risks include effects on both the physical climate system and sociopolitical systems?
Obviously, we'd like to avoid creating a world in which climate engineering is a necessity. Unfortunately, we may be heading down this path. Therefore, we have no choice but to carefully explore climate engineering's potential benefits and risks.
These benefits and risks can be safely explored using computer models and laboratory experiments. (If a decision is made that we need to proceed further, at some point these experiments would have to move outdoors.) These experiments should evaluate both intended and unintended environmental consequences of climate engineering--but we also need to investigate how we might go about constructing such systems, as it's the concrete proposals that will drive the environmental research.
Any real scientific research program will steer clear of value judgments and focus instead on the physical science and technology of climate engineering. Scientists have values, but science is about facts.
Thanks to my colleagues for their thoughtful responses. Geoengineering may indeed prove necessary, temporarily, if the benefits of geoengineering outweigh the negative consequences, and we all agree that much more research is needed to understand the costs, benefits, and potential harm of different scenarios. We also agree that if geoengineering is ever implemented, it must be geoengineering plus mitigation, and never geoengineering instead of mitigation.
Still, I'm concerned that the promise of geoengineering will delay implementation of mitigation. As I say in my essay, reversing global warming is a political problem. In their attempts to maximize profits, the fossil fuel industry has fought the science of global warming so they could continue using the atmosphere as a sewer without charge. The industry exerts tremendous influence in the White House and Congress, and uses the same techniques as the tobacco industry, which recruited scientists to argue that smoking was safe and to confuse the public, thus delaying smoking restrictions and causing countless deaths and suffering.
We are nearing the end of a similar battle with regard to global warming. The latest report from the Nobel Prize–winning Intergovernmental Panel on Climate Change (IPCC) does not present new conclusions; it merely synthesizes and strengthens science we have known for a long time. Yet, think tanks such as the Heartland Institute and the Cato Institute that are funded by fossil fuel interests continue to try to confuse the public. As they begin to embrace geoengineering in an attempt to continue business as usual (the American Enterprise Institute is holding a conference on geoengineering next week), we scientists have to be very careful not to facilitate their efforts.
True, there is little evidence yet of a concerted national or international effort to provide the needed regulations (a gradually increasing carbon tax and a prohibition of new coal plants that lack carbon-capture-and-storage technology) and the requisite research support for new energy technology (i.e., carbon sequestration, improved solar and wind power, and energy efficiency). But this doesn't mean that the regulations and support won't materialize soon. Europe is already leading the way in energy efficiency and regulation, and the United States will soon have a president determined to lead the world in this direction.
Ken Caldeira says that none of my arguments against employing geoengineering is nonnegotiable, but it's the totality of them that needs to be considered. My point about ocean acidification is simply to emphasize that geoengineering won't address all of the consequences of our rising emissions problem. He is wrong about the effects of ozone depletion from geoengineering. (See "The Sensitivity of Polar Ozone Depletion to Proposed Geoengineering Schemes.") And just because Edward Teller suggested that we could engineer our way out of enhanced ultraviolet light, does not make it so. Teller had some other ideas that were pretty bad, to say the least.
I agree with Tom Wigley that we should use "realistic" scenarios and state-of-the-art coupled atmosphere-ocean general circulation models to study the effects of geoengineering. Our recent such study in the Journal of Geophysical Research, shows, for example, that even Arctic-only proposals for atmospheric aerosol seeding would have huge consequences for the African and Asian summer monsoons. The low-intensity geoengineering scenario Tom suggests is only one such scenario, and a new geoengineering research program should take the lead of the IPCC and agree on a set of several common experiments to evaluate.
In contrast to the impressions of Dan Whaley and Margaret Leinen, I am strongly in favor of research on geoengineering and argue for it in my recent Science article, "Whither Geoengineering?" What the international community needs more urgently, though, is research into new energy saving technologies, such as cars that get 200 miles per gallon, public transportation, domestic wind generators that work at low wind speed, and better batteries. And we need to require that all new building roofs that face the equator have built-in solar panels, that all new buildings are built to standards set by the U.S. Green Building Council, and that taxes on huge SUVs make them prohibitively expensive to operate.
A well-funded research program could lessen uncertainties associated with any temporary geoengineering project. But the promise of geoengineering should not delay actions required now to address the root causes of global warming.
My comments are restricted to the type of geoengineering that employs injecting aerosols or aerosol precursors into the stratosphere. This is the primary focus of Alan Robock's article, wherein about half of his arguments against employing this type of geoengineering are related to possible detrimental environmental side effects. Our knowledge of these side effects is still rudimentary. He therefore endorses a "moderate investment in theoretical geoengineering research." His emphasis on "theoretical" accords with his view that we shouldn't undertake even small-scale stratospheric experiments until we know that "we could avoid . . . all of the potential consequences [presumably adverse] that we know about."
Of course, complete avoidance may be impossible--more sensibly, this should be considered a relative risk problem, balancing the possible negative effects of geoengineering against the possibly larger negative effects if we don't pursue geoengineering.
As others have pointed out, no serious scientists suggest deploying any geoengineering strategy now or in the immediate future--at least until we know more about the possible consequences. Nor has anyone suggested we employ geoengineering as a sole climate management strategy, circumventing emissions mitigation. Mitigation is essential, not least because a failure to mitigate would allow carbon dioxide to continue to accumulate in the atmosphere, resulting in further ocean acidification. The primary focus, per my recent Science article, "A Combined Mitigation/Geoengineering Approach to Climate Stabilization," should be on employing geoengineering as a means to gain time to develop and implement cost-effective, carbon-neutral energy technologies that will move us away from our current overwhelming dependence on fossil fuels.
To assess the relative risks of geoengineering to the climate system and stratospheric ozone, we need coupled atmosphere-ocean general circulation models or atmospheric chemistry studies that employ realistic geoenginneering scenarios. No such studies have been published to date. Not only must the geoengineering scenario be realistic (i.e., modeled as part of a combined geoengineering/mitigation strategy), but the results of such a study must be compared with a realistic no-geoengineering scenario.
Possible scenarios for comparison given in my paper are stabilization of atmospheric carbon dioxide at 450 parts per million (ppm) by 2100 through mitigation only, and, as a complementary combined mitigation/geoengineering scenario, an overshoot concentration pathway where atmospheric carbon dioxide reaches 530 ppm before falling back to 450 ppm, coupled with low-intensity geoengineering. These scenarios are projected to have the same effect on global temperature rise--stabilization at about 2 degrees Celsius.
The low-intensity geoengineering case is defined as injecting sulfur dioxide into the stratosphere beginning in 2010, ramping up linearly to a peak of 5 teragrams of sulfur per year between 2040 and 2060, and then declining back to zero by 2090, for a total injection of 130 teragrams of sulfur over 80 years. The consequences of this scenario in terms of sulfur deposition at the Earth's surface (i.e., what is commonly referred to as "acid rain") are likely to be minimal: Globally, 130 teragrams of sulfur is only about two years' worth of current emissions from fossil fuel burning. Optimizing aerosol size and location would require an even smaller injection rate into the stratosphere. Even medium- and high-intensity geoengineering scenarios would lead to relatively little additional surface sulfur deposition when compared to sulfur dioxide emissions scenarios from fossil fuel combustion projected by the Intergovernmental Panel on Climate Change. Likewise, the effect of stratospheric aerosol loading on cirrus clouds is likely to be minor, and the slow ramp-up would give people plenty of time to adapt to suggested changes in the blueness of the sky.
Of course, as Alan points out, regional differences in surface sulfur deposition are possible--the effects from geoengineering are likely to be larger in more pristine areas--and the patterns of deposition resulting from injecting aerosols into the stratosphere are likely to be different from those due to fossil-fuel burning. Further work is required to elucidate these flux patterns, but it's highly unlikely that they would present a significant problem.
Indeed, I cannot see any scientific reason why the low-intensity geoengineering case could cause detrimental effects of a magnitude that would outweigh the positive effects of geoengineering, the key benefit being significantly more time to develop and deploy the carbon-neutral technologies needed for climate stabilization. Alan has a rosy view of our ability to develop these technologies in a timely fashion, which is at odds with many economists and energy experts. The hurdles are immense, not just politically, but also in terms of technology. (See "Dangerous Assumptions" and "Sustainable Developments: Keys to Climate Protection.") Given the uncertainty of meeting the technological challenges, we should treat geoengineering as a real possibility and meet it head on at a funding level that will bring results and reduce uncertainties quickly.
Although Alan Robock's "20 Reasons Why Geoengineering May Be a Bad Idea" raises legitimate questions, it seems to argue against implementation rather than against studying the underlying science. Few people are actively advocating for immediate, full-scale implementation of geoengineering techniques as a means of addressing climate change. But many people are suggesting that we learn more about the efficacy of such techniques--including Alan, who was recently awarded a National Science Foundation grant to study the effectiveness and possible consequences of injecting aerosol particles into the stratosphere to reduce incoming solar radiation.
In terms of geoengineering concerns, it's helpful to group them into three categories:
Efficacy. Clearly, any geoengineering technique first needs to achieve the intended effect for a reasonable cost--whether the goal is buying time for more sustainable solutions by reducing incoming solar radiation or addressing the root cause of warming by removing carbon dioxide from the atmosphere. It's critical that scientists be allowed to study efficacy through experimentation and modeling without being stigmatized by the assumption that their work will cause a rush to full implementation.
Impact. The environmental impacts of the technique must either be minimal or acceptable relative to the benefits of action and the consequences of inaction. Martin Bunzl makes this point clearly in "An Ethical Assessment of Geoengineering," an accompanying essay on p. 18 of Alan's article. In the case of ocean iron fertilization, 12 small, open-ocean experiments have already been conducted by oceanographers to improve understanding of both efficacy and impacts. (See "Mesoscale Iron Enrichment Experiments 1993-2005: Synthesis and Future Directions".) From the start, it was clear that these experiments weren't a danger to the environment and that their effects wouldn't last long. Scientists should be encouraged to study impacts through experimentation and modeling as long as it can be reasonably presumed that their impacts are short-lived.
Implementation. If a technique is both effective and sensitive to the environment, the following implementation questions become important: Who implements it? Who regulates it? And how do we incorporate these activities into existing regulatory and legal frameworks and treaties? These questions are difficult but not intractable, as many carefully negotiated international agreements already demonstrate, including the International Maritime Organization's London Convention on ocean dumping (signed by 80 countries in 1972, including most of the developed world) and the U.N. Law of the Sea treaty (signed and ratified by most countries except the United States).
More broadly, the provocative title of Alan's article and the quick treatment of individual concerns obscure the complexity behind these subject areas--as Martin and Ken Caldeira have addressed. We expected a summary of research results suggesting a priori that geoengineering is a bad idea, but didn't find one. Also, we found it distracting that many of Alan's concerns (i.e., ozone depletion, acid deposition, effects on cirrus clouds and plants) are specific to one technique--aerosol seeding--but offered as reasons why geoengineering in general is a bad idea. Another of Alan's examples presumes that "humans [adopt] geoengineering as a solution to global warming, with no restriction on continued carbon emissions." No one is suggesting that geoengineering replace emissions reduction.
Most surprising is Alan's conclusion that global warming is a not a difficult technical--but rather purely a political--problem, and therefore, geoengineering isn't required to solve it. We disagree. The road ahead is paved with difficult technical challenges in addition to the considerable political ones. Many new, clean technologies that promise incremental improvements in efficiency also require substantial scientific achievements--such as genetic modification of organisms to make novel substances (i.e., enzymes that process various feedstocks for cellulosic ethanol) or revolutionary advances in materials and process sciences (i.e., new thin-film technologies for solar power). Emission reductions don't simply follow from mandates; we must innovate alternatives to fossil fuels.
That we need to contemplate geoengineering to buy us time for that innovation is unfortunate. That we have the scientific, technical, and human potential to do so responsibly is not.
Winston Churchill once famously said, "Democracy is the worst form of government except all the others that have been tried." Climate engineering may indeed be a bad idea, but so far, better ideas to mitigate global warming show little traction.
We can all agree that eliminating carbon emissions is the right thing to do and that everyone in the world should set aside narrow short-tem self interest and instead work together to provide a better environment for future generations. And when Alan Robock provides 20 reasons why geoengineering may be a bad idea, we can all agree--it is a bad idea. However, what we appear to be achieving in the meantime may be much worse. For all the recent talk about reducing carbon dioxide emissions, the concentration of atmospheric carbon dioxide is growing more rapidly than supposedly pessimistic scenarios predicted even a few years ago.
Preliminary climate model simulations show that in a high-carbon-dioxide world, Earth's climate would be more similar to that of several centuries ago with climate engineering than without it. It won't work perfectly, but imperfection isn't an argument against improvement. The question is whether, in the face of rising greenhouse gas concentrations, climate engineering will improve environmental conditions or merely make things worse. This is an open research question that needs to be vigorously pursued, but an examination of a few of the criticisms on Alan's list demonstrates that so far, none are nonnegotiable:
Continued ocean acidification. Emissions reduction and climate engineering are two levers of action that can be employed jointly or separately. Ocean acidification is a consequence of excess atmospheric carbon dioxide getting dissolved into the ocean, not climate engineering. Climate engineering cannot reverse every adverse consequence of carbon dioxide emissions, but no thoughtful person ever claimed it would.
Ozone depletion. The Mount Pinatubo eruption lofted more than enough aerosols into the atmosphere to compensate for a doubling of atmospheric carbon dioxide, yet ozone concentrations fell by only 3 percent. And it's believed that this small reduction was caused by chlorine from human-made chlorofluorocarbons, which are now banned by the Montreal Protocol. So while the threat to the ozone layer is worth studying in greater detail, it's expected to diminish with time. Furthermore, schemes have been proposed that might preferentially scatter ultraviolet radiation, compensating for any minor reduction in the protection that the ozone provides us from ultraviolet light.
Effects on plants. Alan is correct that we need to study possible effects of climate engineering on plant growth. After the Mount Pinatubo eruption, vegetation everywhere grew more vigorously, taking up more carbon from the atmosphere. This is because diffuse sunlight is able to reach down to enhance photosynthesis in the lower leaves of forest trees, which are normally shaded by the upper canopy in direct sunlight. In general, plant growth responds almost linearly to changes in the amount of sunlight--a 2-percent reduction in sunlight might be expected to produce 2 percent less photosynthesis. But people growing crops in greenhouses often elevate the carbon dioxide level to fertilize their plants, and this effect is typically larger than 2 percent. Therefore, it's possible that a high-carbon-dioxide world with slightly reduced but more scattered sunlight would have higher crop yields than today's world. In computer simulations, vegetation grew more vigorously in an engineered high-carbon-dioxide world than it did in the natural low-carbon-dioxide world. Of course, we can expect these changes to affect natural ecosystems in unforeseen ways, and so should certainly be the subject of intense study.
More acid deposition. The amount of sulfur used in a climate engineering system would be a small percentage of today's emissions from power plants. So if current sulfur emissions regulations were tightened by a few percent when such a system was deployed, there would be no increase in overall sulfur emissions. Furthermore, there's nothing magical about sulfur--other compounds such as silica or calcium carbonate could be used to scatter incoming sunlight, although perhaps at somewhat greater economic cost.
I'll leave Alan's other points for future missives, but the take-home message is, preliminary climate model simulations indicate that climate engineering may mitigate some but not all of the effects of rising greenhouse gas concentrations. While we might prefer near-universal cooperation in carbon dioxide emissions reduction, it's clearly time to plan what we will do if those emissions reductions don't come quick enough or are not deep enough to prevent a climate crisis. The question isn't whether we need to plan for such an eventuality, but what form that planning should take.
