Can geoengineering safely mitigate the effects of climate change?
Since the dawn of the Industrial Revolution, mankind has unintentionally altered and engineered Earth's climate. By continuously adding industrial byproducts like greenhouse gases into the air, anthropogenic action has sped up the rate or global warming. To scientists like Ken Caldeira, a lead scientist in geoengineering research, it makes perfect sense to mitigate the harmful effects of climate change through the intentional alteration of climatic activity. In an interview, he points out that it is not only favorable, but needed, because of climatic inertia. Even if carbon dioxide emissions were reduced to 0 today, warming would continue for decades, possibly even centuries. The rate of warming we are experiencing can lead to crop failures and wide spread famines. Even if grandiose emissions reductions were possible within our current global-political framework, we still have to mitigate the effects of warming that will continue as CO2 remains in the air. Caldiera suggests that a mix of emissions reduction and geoengineering strategies can be a more effective solution in combating global climate change (1).
The exact climatic effects of geoengineering projects, solar radiation management (SRM) techniques in particular, are extremely uncertain. At this current state of research, scientists are reliant on climatic computer models and past volcanic activity in projecting the effects of sulfur aerosol release, a commonly discussed SRM technique. The Mt. Pinatubo volcanic eruption in the Philippines in 1991 has been the most intensely studied volcano in the field of atmospheric aerosol research. Following the eruption, the Earth experienced a cooling effect that lasted for approximately 2 years. The amount of sulfur that was released into the air was enough to reflect 5% of the Sun's energy back into space before it reached, and was absorbed, by the atmosphere. A year following the eruption, the Earth had a mean average temperature that was approximately 0.5 degrees Celsius cooler than the previous year. The graphs below show the rates of aerosol concentration with the mean temperature change plotted over the same time scale to compare the two values. This clearly shows a correlation between the aerosol concentration and cooling effect experienced over time. Many scientists believe that a constant, long-term release of sulfur can greatly reduce the absorption of solar radiation in the atmosphere and can lead to greater global cooling trends into the future. Sulfur aerosol release can be an effective strategy in combating climate change (2).
The predictions made above are inconclusive; not all models and estimations of the effects of sulfur release project a positive reaction to a constant aerosol injection. Unsatisfied with other scientists' work, researchers Alan Robock, Luke Oman and Georgiy Stenchikov proceeded to evaluate the issue themselves. To simulate climatic dispersion and effects of aerosols, the researchers used a comprehensive general circulation model that included the interactive injection, transport and removal of stratospheric aerosol and studied the time-dependent climate system response. The model was ran multiple times studying the release of different SO2 concentrations in both tropical and arctic areas over a 20 year time period. The results from this model show that geoengineering will produce an average global cooling effect but will have detrimental, regional warming effects in certain areas. The hydrological cycle will also be altered, interrupting the African and Asian monsoon systems, reducing food and water supplies in densely populated areas. The use of aerosol injection in the Arctic to protect sea ice will have grave effects on lower latitude environments as aerosols disperse. If the aerosol injection programs discontinue for any reason, the planet will experience a rapid warming that will be much more harmful than a gradual global warming (3).
Outside of computer modeling and projections based on real world events, there is no safe way to test the real world effects and application of aerosol programs. Geoengineering testing is not only risky, but it invites a whole slew of political and ethical dilemmas. Global debates would occur and agreements would have to be reached on how tests should be implemented and regulated. Many would argue that smaller scale testing won't help us accurately understand the full risks involved in a large scale deployment. Scientists like David Keith suggest incremental testing where small-scale experiments are done at first and are scaled up can be an effective, politically acceptable solution. Others argue that the initial, small experiments would lead to inaccurate results so there is no point in conducting them. Field testing may not be practical or feasible, meaning if a climate crisis does occur, there is a good chance that geoengineering projects will be implemented without real-world experimentation to gauge the effects, both good and bad (4).
(2) Blackstock, J. J., Battisti, D.S., Caldeira, K., Eardley, D.M., et al. (2009, July 29). Climate engineering responses to climate emergencies. (Novim, 2009). archived online at: http://arxiv.org/pdf/0907.5140
(3) Robock, A., Oman, L. & Stenchikov, G. (2008). Regional climate responses to geoengineering with tropical and arctic SO2 injections. Journal of Geophysical Research: 1-33.