"Geoengineering" is the idea of taking purposeful action to mitigate the effects of inadvertent global greenhouse warming. While a number of schemes have been proposed, the most plausible involve reducing the intensity of solar radiation reaching Earth's surface, either by injecting particles into the stratosphere or by stationing reflectors between the Earth and the Sun in space at the first Lagrange point (L1).
This program of modeling studies will address how such injected aerosols would behave and how the solar shading would affect the climate. In addition, the policy and ethical considerations of these geoengineering schemes will be analyzed.
Plausible scenarios for geoengineered aerosol injections and L1 sun-shading will be generated. Modules will be developed to calculate the detailed evolution of the injected aerosols in climate models. Global circulation models will then be run using these scenarios and modules. These experiments will address a wide range of questions about geoengineering, including the possible increase in acidic precipitation from the injection of sulfate aerosol, the increase in diffuse and decrease in direct solar radiation, regional climate changes, the potential for rapid severe warming if or when the aerosol injection ceases, interactions between the effects of natural volcanic and geoengineered aerosols, effects on cirrus clouds, interactions with natural climate variations such as El Nino, and contributions to tropospheric burdens of pollutants.
The experiments will involve the introduction of detailed aerosol evolution schemes into two climate models, the Goddard Space Flight Center GEOS5 model, which features high spatial resolution, and the Goddard Institute for Space Studies (GISS) ModelE, which has lower resolution and will be used for exploratory experiments.
Co-investigator Bunzl, from Rutger's Department of Philosophy, will serve as a bridge between the climate modeling work and social scientists, who will be invited to study the model results and use them in social-science models. The potential risks and benefits of geoengineering will be analyzed and the extent to which these are distributed unevenly across communities and regions will be considered.
The broader impacts of this project stem from the need for studies, such as this, to inform policy makers and the public regarding the potential costs and benefits of different geoengineering schemes.
This grant supported work on three related topics, the effects of volcanic eruptions on climate, the impacts of stratospheric geoengineering on climate, and the impacts nuclear war on climate. For each of these topics, this report provides a brief summary of the results. High latitude volcanic eruptions in the spring and summer have a much larger climatic impact than those in fall or winter, because the resulting upper atmosphere clouds have a lifetime of 3-4 months, and those in the fall or winter would fall out before they had a chance to reflect sunlight. The 2008 Okmok and Kasatochi and 2009 Sarychev volcanic eruptions had small impacts on climate. The 2011 Nabro eruption was the largest eruption since Pinatubo in 1991, and created a stratospheric cloud, not by direct injection of the sulfur dioxide gas, but because subsequent summer monsoon circulation pumped the sulfur from the upper troposphere to the lower stratosphere. Coupled Model Intercomparison Project 5 (CMIP5) simulations did not do a good job of simulating the Northern Hemisphere winter circulation response to volcanic eruptions. The 1783 Laki eruption did produce a stratospheric aerosol cloud and was partly responsible for the cold Northern Hemisphere winter of 1783-1784. There are at least 20 reasons why stratospheric geoengineering may be a bad idea. While continuous injection of sulfur dioxide gas into the lower stratosphere either in the Tropics or Arctic could produce a sulfuric acid cloud that could cool the planet, both would produce irregular patterns of precipitation response, with a weakening of the summer African and Asian monsoons. The additional acid deposition from such schemes would not be very dangerous in itself. In theory, it would cost a few billion dollars per year to take enough sulfur into the stratosphere to produce a cloud that could significantly cool the climate, but not only is there currently no equipment that could do it, we also have no way to create cloud droplets that would stay small enough to be effective at scattering sunlight. In the meantime, if we could do that, they would destroy ozone and increase ultraviolet radiation at the surface. Using soot for stratospheric geoengineering would require less material than for sulfur, but it would have a much larger impact on ozone and be very expensive. Stratospheric geoengineering cannot be tested outdoors without a large-scale implementation, because it would be necessary to study how cloud droplets grow in size in the presence of an existing cloud, and the climate response would need a large signal to be detected. Geoengineering will probably never be used, as the governance issues would be insurmountable. Indoor geoengineering research is ethical, as the need to know what its benefits and risks might be outweigh the possible negative aspects. Outdoor geoengineering research is not ethical, unless governed by an independent environmental impacts assessment. We have established the Geoengineering Model Intercomparison Project (GeoMIP) to study the impacts of geoengineering with a standard set of climate model experiments. A nuclear war between India and Pakistan, with each country using 50 Hiroshima-sized atomic bombs as airbursts on urban areas, could produce climate change unprecedented in recorded human history, global-scale ozone depletion, and widespread famine. Agricultural production could fall by 10-20% for a decade in the U.S. and China, the world’s largest grain producing regions. Furthermore, although the total number of nuclear weapons in the world is about 1/3 of the peak number in the 1980s, a large-scale conflict between the U.S. and Russia could still produce a full nuclear winter, and the effects of regional and global nuclear war would last for more than a decade, much longer than previously thought. Nuclear winter will still be possible even after full implementation of the New Start Treaty in 2017. The continued existence of nuclear weapons implies a grave threat to life on Earth not just from the direct effects of the weapons, but also from the potentially much larger environmental threats. The best solution to avoid nuclear war impacts on agriculture is to avoid nuclear war, and this can only be guaranteed with a nuclear-weapon-free world. In fact, the current situation is one of self-assured deterrence, in which a nuclear attack on another nation would be suicide for the nation conducting the attack, even with no nuclear response, due to the ensuing impacts on climate and agricultural production.
