Local Chemtrails? Regional Solar Geoengineering Proposed

Critics of geoengineering have long warned that such a global intervention would have unequal effects around the world and could result in unforeseen consequences. They argue that the potential gains may not be worth the risk.

“Our research goes a step beyond the one-size-fits-all approach to explore how careful tailoring of solar geoengineering can reduce possible inequalities and risks,” says co-author David Keith, Gordon McKay Professor of Applied Physics at the Harvard School of Engineering and Applied Sciences (SEAS) and Professor of Public Policy at Harvard Kennedy School. “Instead, we can be thoughtful about various tradeoffs to achieve more selective results, such as the trade-off between minimizing global climate changes and minimizing residual changes at the worst-off location.”

The study—developed in collaboration with Douglas G. MacMartin of the California Institute of Technology, Ken Caldeira of the Carnegie Institution for Science, and Ben Kravitz, formerly of Carnegie and now at the Department of Energy—explores the feasibility of using solar geoengineering to counter the loss of Arctic sea ice.

 

Sunset in the Arctic. A new study at Harvard explores the feasibility of using cautious and targeted solar geoengineering to counter the loss of Arctic sea ice. 

File photo courtesy of NASA/Kathryn Hansen

“There has been a lot of loose talk about region-specific climate modification. By contrast, our research uses a more systematic approach to understand how geoengineering might be used to limit a specific impact. We found that tailored solar geoengineering might limit Arctic sea ice loss with several times less total solar shading than would be needed in a uniform case.” 

 

Generally speaking, greenhouse gases tend to suppress precipitation, and an offsetting reduction in the amount of sunlight absorbed by Earth would not restore this precipitation. Both greenhouse gases and aerosols affect the distribution of heat and rain on this planet, but they change the temperature and precipitation in different ways in different places. The researchers suggest that varying the amount of sunlight deflected away from the Earth both regionally and seasonally could combat some of this problem.

“These results indicate that varying geoengineering efforts by region and over different periods of time could potentially improve the effectiveness of solar geoengineering and reduce climate impacts in at-risk areas,” says co-author Ken Caldeira, Senior Scientist in the Department of Global Ecology at the Carnegie Institution for Science.

The researchers note that while their study used a state-of-the-art model, any real-world estimates of the possible impact of solar radiation management would need to take into account various uncertainties. Further, any interference in Earth’s climate system, whether intentional or unintentional, is likely to produce unanticipated outcomes.

“While more work needs to be done, we have a strong model that indicates that solar geoengineering might be used in a far more nuanced manner than the uniform one-size-fits-all implementation that is often assumed. One might say that one need not think of it as a single global thermostat. This gives us hope that if we ever do need to implement engineered solutions to combat global warming, that we would do so with a bit more confidence and a great ability to test it and control it.”

 

Solar radiation management is a class of theoretical concepts for manipulating the climate in order to reduce the risks of global warming caused by greenhouse gasses. But its potential effectiveness and risks are uncertain, and it is unclear whether tests could help narrow these uncertainties. A team composed of Caltech’s Doug MacMynowski, Carnegie’s Ken Caldeira and Ho-Jeong Shin, and Harvard’s David Keith used modeling to determine the type of testing that might be effective in the future. 

Credit: Carnegie Institute

 

Ideas for solar radiation management include increasing the amount of aerosols in the stratosphere, which could scatter incoming solar heat away from Earth’s surface, or creating low-altitude marine clouds to reflect these same rays. Clearly the size of the scale and the intricacies of the many atmospheric and climate processes make testing these ideas difficult.
The authors declare no competing financial interests.

Research models have indicated that the climatic effect of this type of geoengineering will vary by region, because the climate systems respond differently to the reflecting substances than they do to the atmospheric carbon dioxide that traps warmth in Earth’s atmosphere. New work from a team including Carnegie’s Ken Caldeira uses a climate model to look at maximizing the effectiveness of solar radiation management techniques. Their work is published October 21st by Nature Climate Change.

Attempting to counteract the warming effect of greenhouse gases with a uniform layer of aerosols in the stratosphere, would cool the tropics much more than it affects polar areas. Greenhouse gases tend to suppress precipitation and an offsetting reduction in amount of sunlight absorbed by Earth would not restore this precipitation. Both greenhouse gases and aerosols affect the distribution of heat and rain on this planet, but they change temperature and precipitation in different ways in different places. Varying the amount of sunlight deflected away from the Earth both regionally and seasonally could combat some of this problem.

By tailoring geoengineering efforts by region and by need, the team—led by California Institute of Technology’s Douglas MacMartin—was able to explore ways to maximize effectiveness while minimizing the side effects and risks of this type of planetary intervention.

“These results indicate that varying geoengineering efforts by region and over different periods of time could potentially improve the effectiveness of solar geoengineering and reduce climate impacts in at-risk areas,” Caldeira said. “For example, these approaches may be able to reverse long-term changes in the Arctic sea ice.”

The study used a sophisticated climate model, but the team’s model is still much simpler than the real world. Interference in Earth’s climate system, whether intentional or unintentional, is likely to produce unanticipated outcomes.

“We have to expect the unexpected,” Caldeira added. “The safest way to reduce climate risk is to reduce greenhouse gas emissions.”

 Contacts and sources:
Harvard School of Engineering and Applied Sciences