Geoengineering and sustainability

ABSTRACT

Geoengineering is regarded by advocates as a creative and responsible technological option in the face of a climate emergency. Critics often see it as a hubristic attempt to play God, with disastrous consequences for the planet and humanity. These antipodal perspectives are represented by the ideal types of Prometheans and Gaians. Prometheans and Gaians typically talk past each other. The geoengineering debate can be made more fruitful by well articulating their respective positions and subsequently situating them in the discourse of sustainability. A sustainability orientation does not answer the troubling question whether geoengineering should be developed and deployed. But it can foster a ‘fusion of horizons’ between Prometheans and Gaians, providing common ground in an otherwise polarized debate and making a more productive dialogue possible.     

On integration of policies for climate and global change

Currently envisaged mitigation of greenhouse gases (GHG) emissions will be insufficient to appreciably limit climate change and its impacts. Adaptation holds the promise of ameliorating the impacts on a small subset of systems being affected. There is no question that both will be needed. However, climate change is only part of a broader multi-stress setting of global through to local changes. Privileging climate related policies over other concerns leads to tragic outcomes. Climate policies need to be designed for and integrated into this broader and challenging context. This paper focuses on placing climate change within the broader context of global change and the importance of aligning climate policy objectives with the myriad other policies that still need to be implemented if our primary goal is improving human welfare rather than limiting our focus to climate change and its impacts.     

Influence of Geoengineered Climate on the Terrestrial Biosphere

Various geoengineering schemes have been proposed to counteract anthropogenically induced climate change. In a previous study, it was suggested that a 1.8% reduction in solar radiation incident on the Earths surface could noticeably reduce regional and seasonal climate change from increased atmospheric carbon dioxide (CO₂). However, the response of the terrestrial biosphere to reduced solar radiation in a CO₂-rich climate was not investigated. In this study, we hypothesized that a reduction in incident solar radiation in a Doubled CO₂ atmosphere will diminish the net primary productivity (NPP) of terrestrial ecosystems, potentially accelerating the accumulation of CO₂ in the atmosphere. We used a dynamic global ecosystem model, the Integrated Biosphere Simulator (IBIS), to investigate this hypothesis in an unperturbed climatology. While this simplified modeling framework effectively separated the influence of CO₂ and sunlight on the terrestrial biosphere, it did not consider the complex feedbacks within the Earths climate system. Our analysis indicated that compared to a Doubled CO₂ scenario, reduction in incident solar radiation by 1.8% in a double CO₂ world will have negligible impact on the NPP of terrestrial ecosystems. There were, however, spatial variations in the response of NPP-engineered solar radiation. While productivity decreased by less than 2% in the tropical and boreal forests as hypothesized, it increased by a similar percentage in the temperate deciduous forests and grasslands. This increase in productivity was attributed to a 1% reduction in evapotranspiration in the Geoengineered scenario relative to the Doubled CO₂ scenario. Our initial hypothesis was rejected because of unanticipated effects of engineered solar radiation on the hydrologic cycle. However, any geoengineering approaches that reduce incident solar radiation need to be thoroughly analyzed in view of the implications on ecosystem productivity and the hydrologic cycle.     

Ecosystem Impacts of Geoengineering: A Review for Developing a Science Plan

Geoengineering methods are intended to reduce climate change, which is already having demonstrable effects on ecosystem structure and functioning in some regions. Two types of geoengineering activities that have been proposed are: carbon dioxide (CO(2)) removal (CDR), which removes CO(2) from the atmosphere, and solar radiation management (SRM, or sunlight reflection methods), which reflects a small percentage of sunlight back into space to offset warming from greenhouse gases (GHGs). Current research suggests that SRM or CDR might diminish the impacts of climate change on ecosystems by reducing changes in temperature and precipitation. However, sudden cessation of SRM would exacerbate the climate effects on ecosystems, and some CDR might interfere with oceanic and terrestrial ecosystem processes. The many risks and uncertainties associated with these new kinds of purposeful perturbations to the Earth system are not well understood and require cautious and comprehensive research.     

Are there reasons against open-ended research into solar radiation management? A model of intergenerational decision-making under uncertainty

Solar radiation management (SRM) has been proposed as a means of last resort against dangerous climate change. We propose a stylized model of intergenerational decision making on SRM research, greenhouse-gas abatement and SRM deployment, under uncertainties about (a) the extent of future climate damage and (b) effectiveness and potential harmful side-effects of SRM. Open-ended research may reveal either that SRM effectively reduces climate damage, or that it would cause more harm than benefits. We find that SRM research increases the likelihood of deployment (“slippery slope”), and derive conditions that it decreases abatement effort in expectation (“moral hazard”). Neither of these provides a rationale against SRM research, though. The rational decision is to perform SRM research, unless (i) discounting is hyperbolic and (ii) the absolute prudence of expected climate damage is smaller than absolute risk aversion. These results generalize to the case where SRM research also provides information on climate sensitivity.