Current and Future Research Directions of Aerosol Climate Engineering

Climate engineering approaches to counter some of the anthropogenic global warming have been proposed for a while, starting in 1965 with a report to President Lyndon Johnson from his scientific advisory committee. In 1974, Mikhail Budyko was the first to propose creation of a stratospheric aerosol cloud to reflect sunlight and cool Earth. The review paper by Robert Dickinson in 1996 summarized climate engineering approaches that are still the focus of open research questions today. These approaches include using aerosols as solar “reflectors” and seeding clouds with aerosols to increase their amount and brightness, in addition to exploring carbon dioxide capture and removal techniques. Dickinson and others at the time called for an assessment of solar radiation management (SRM) approaches and their side effects, including effects on the hydrological cycle and the ozone layer. Ten years later in 2006, a paper by Nobel Prize laureate Paul Crutzen triggered an upward trend in research to explore effects of climate engineering approaches, in particular using sulfate aerosols. In parallel, early studies addressed the question of how aerosols may be used to brighten the clouds and make them more reflective, similar to what has been observed from ship tracks. Improved understanding of these proposed methods has been gained especially after the launch of the Geoengineering Model Intercomparison Project (GeoMIP), using simplified experiments in state-of-the-art climate models. Nevertheless, limited support for research in this area is keeping many questions unanswered. With greenhouse gas emissions still continuing to increase, human-caused climate change is predicted to worsen in the future. Climate engineering approaches may therefore be the only option to help reach important temperature targets and to prevent significant impacts on society and ecosystem. However, important questions need to be addressed before these options can be considered, including feasibility and efficiency of these applications and their side effects. Modeling studies in recent years have investigated new ways to strategically apply climate engineering approaches with the goal to increase benefits and reduce side effects. Efforts like the Geoengineering Large Ensemble Project using a comprehensive Earth system model and the Developing Country Impacts Modelling Analysis for SRM, have been initiated in order to explore benefits, side effects and risks of stratospheric aerosol geoengineering. Still, very little has been done so far to investigate effects on society and ecosystems. Looking back to Dickinson’s review paper, a thorough assessment of climate engineering strategies is still needed, however, with increasing urgency.