U54A-01 INVITED
Modeling the Climatic Consequences of Geoengineering
The last half-century has seen the development of physically comprehensive computer models of the climate system. These models are the primary tool for making predictions of climate change due to human activities, such as emitting greenhouse gases into the atmosphere. Because scientific understanding of the climate system is incomplete, however, any climate model will necessarily have imperfections. The inevitable uncertainties associated with these models have sometimes been cited as reasons for not taking action to reduce such emissions. Climate models could certainly be employed to predict the results of various attempts at geoengineering, but many questions would arise. For example, in considering proposals to increase the planetary reflectivity by brightening parts of the land surface or by orbiting mirrors, can models be used to bound the results and to warm of unintended consequences? How could confidence limits be placed on such model results? How can climate changes due to proposed geoengineering be distinguished from natural variability? There are historical parallels on smaller scales, in which models have been employed to predict the results of attempts to alter the weather, such as the use of cloud seeding for precipitation enhancement, hail suppression and hurricane modification. However, there are also many lessons to be learned from the recent record of using models to simulate the effects of the great unintended geoengineering experiment involving greenhouse gases, now in progress. In this major research effort, the same types of questions have been studied at length. The best modern models have demonstrated an impressive ability to predict some aspects of climate change. A large body of evidence has already accumulated through comparing model predictions to many observed aspects of recent climate change, ranging from increases in ocean heat content to changes in atmospheric water vapor to reductions in glacier extent. The preponderance of expert opinion is that this evidence is now sufficient to establish the human cause of much recent climate change. Nevertheless, no model can provide detailed and fully trustworthy answers to every possible question of interest. As an example, how will the climatology of Atlantic hurricanes change as the greenhouse effect becomes stronger? Can models reliably forecast changes in the length of the hurricane season or changes in the geographical regions affected by hurricanes? The answer is no, or at least, not yet. Additionally, climate models are not based entirely on first principles, such as Newtonian physics. Instead, they have been developed primarily to simulate the present climate and relatively small departures from it. To achieve this goal, a certain amount of empiricism has been built into the models. The result has sometimes been to increase the apparent realism of models at the cost of limiting their generality. Thus, the available climate models may well be less capable of simulating a geoengineering experiment that might lead to a radically different climate. New model development may be required for this new application. The challenge is to distinguish between what models can and cannot do well. It would be irresponsible and unethical, either to undertake geoengineering projects without modeling their consequences, or to place blind faith in the models. To decide how best to model a proposed geoengineering technique requires a deep understanding of the strengths and weaknesses of climate models. The history of modeling successes and failures is a valuable guide to the wise interpretation of model results.
U54A-02 INVITED
Engineering the earth system
The post-war growth of the earth sciences has been fueled, in part, by a drive to quantify environmental insults in order to support arguments for their reduction, yet paradoxically the knowledge gained is grants us ever greater capability to deliberately engineer environmental processes on a planetary scale. Increased capability can arises though seemingly unconnected scientific advances. Improvements in numerical weather prediction such as the use of adjoint models in analysis/forecast systems, for example, means that weather modification can be accomplished with smaller control inputs. Purely technological constraints on our ability to engineer earth systems arise from our limited ability to measure and predict system responses and from limits on our ability to manage large engineering projects. Trends in all three constraints suggest a rapid growth in our ability to engineer the planet. What are the implications of our growing ability to geoengineer? Will we see a reemergence of proposals to engineer our way out of the climate problem? How can we avoid the moral hazard posed by the knowledge that geoengineering might provide a backstop to climate damages? I will speculate about these issues, and suggest some institutional factors that may provide a stronger constraint on the use of geoengineering than is provided by any purely technological limit.
U54A-03 INVITED
Fantasy and Reality in the History of Weather and Climate Control
This presentation examines the history of large-scale weather and climate engineering since 1840, with special reference to imaginative and speculative literature and with special relevance to ethical and policy issues. Ultimate control of the weather and climate embodies both our wildest fantasies and our greatest fears. Fantasy often informs reality (and vice-versa). NASA managers know this well, as do Trekkies. The best science fiction authors typically build from the current state of a field to construct futuristic scenarios that reveal and explore the human condition. Scientists as well often venture into flights of fancy. Though not widely documented, the fantasy-reality axis is also a prominent aspect of the history of the geosciences. James Espy's proposal in the 1840s to enhance precipitation by lighting huge fires, thus stimulating convective updrafts, preceded the widespread charlatanism of the rain-makers, or so-called "pluviculturalists," in the western U.S. One hundred years later, promising discoveries in "cloud seeding" by Irving Langmuir and his associates at the General Electric Corporation rapidly devolved into unsupportable proposals and questionable practices by military and commercial rain-makers seeking to control the weather. During the Cold War, Soviet engineers also promoted a chilling vision (to Westerners) of global climate control. Recently, rather immodest proposals to "fix" a climate system perceived to be out of control have received wide circulation. In 2003 the U.S. Pentagon released a report recommending that the government should "explore geo-engineering options that control the climate." In 2004 a symposium in Cambridge, England set out to "identify, debate, and evaluate" possible, but highly controversial options for the design and construction of engineering projects for the management and mitigation of global climate change. This talk will locate the history of weather and climate modification within a long tradition of imaginative and speculative literature involving "control" of nature. The goal is the articulation of a perspective fully informed by history and the initiation of a dialogue, stimulated by this approach, that uncovers otherwise hidden values, ethical implications, social tensions, and public apprehensions.
U54A-04 INVITED
Geoengineering the Climate: Approaches to Counterbalancing Global Warming
For the past two hundred years, the inadvertent release of carbon dioxide and other radiatively active gases and aerosols, particularly as a result of combustion of fossil fuels and changes in land cover, have been contributing to global climate change. Global warming to date is approaching 1°C, and this is being accompanied by reduced sea ice, rising sea level, shifting ecosystems and more. Rather than sharply curtailing use of fossil fuels in order to reduce CO2 emissions and eventually eliminate the net human influence on global climate, a number of approaches have been suggested that are intended to advertently modify the climate in a manner to counter-balance the warming influence of greenhouse gas emissions. One general type of approach is carbon sequestration, which focuses on capturing the CO2 and then sequestering it underground or in the ocean. This can be done at the source of emission, by pulling the CO2 out of the atmosphere through some chemical process, or by enhancing the natural processes that remove CO2 from the atmosphere, for example by fertilizing the oceans with iron. A second general approach to geoengineering the climate is to lower the warming influence of the incoming solar radiation by an amount equivalent to the energy captured by the CO2-induced enhancement of the greenhouse effect. Proposals have been made to do this by locating a deflector at the Earth-Sun Lagrange point, lofting many thousands of near-Earth mirrors, injecting aerosols into the stratosphere, or by increasing the surface albedo. A third general approach is to alter natural Earth system processes in ways that would counterbalance the effects of the warming. Among suggested approaches are constructing dams to block various ocean passages, oceanic films to limit evaporation and water vapor feedback, and even, at small scale, to insulate mountain glaciers to prevent melting. Each of these approaches has its advantages, ranging from simplicity to reversibility, and disadvantages, ranging from costs for implementation to associated inadvertent negative environmental consequences. Unless implemented as only a bridging effort, geoengineering would require diversion of substantial, and even growing, resources from the effort to move away from reliance on fossil fuels. Because the lifetime of the excess CO2 in the atmosphere is so long, such efforts would generally need to be maintained for centuries by future generations to avoid a relatively rapid increase in global average temperature, even after emissions of CO2 had eventually been halted. In that such approaches are also fraught with uncertainties, there has been very little study of the details of how such approaches might be pursued and of their overall advertent and inadvertent consequences, leaving the area open to ongoing consideration of sometimes rather speculative possibilities.