Solar Geoengineering Could Help Offset Global Warming

One of the main misapprehensions about solar geoengineering—injecting aerosols into the atmosphere to reflect sunlight and decrease global warming—is that it could be used as a universal remedy to invert global warming trends and revert temperature back to pre-industrial levels.

But this is not possible. Applying high doses of solar geoengineering to counterbalance global warming caused by increased carbon dioxide levels in the atmosphere could heighten the climate problem—specifically rainfall patterns—in particular regions. However, could low doses work in alignment with the reduction in emission to decrease the risks of a changing climate?

A novel study by the scientists from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), together with MIT and Princeton University, has indicated that if solar geoengineering were used to decrease half of the increased global temperature, then there could be global advantages without worsening the change in any huge geographical area.

Some of the problems identified in earlier studies where solar geo-engineering offset all warming are examples of the old adage that the dose makes the poison. This study takes a big step towards using climate variables most relevant for human impacts and finds that no IPCC-defined region is made worse off in any of the major climate impact indicators. Big uncertainties remain, but climate models suggest that geoengineering could enable surprisingly uniform benefits.

David Keith, Study Senior Author, Gordon McKay Professor of Applied Physics, Harvard SEAS.

This study has been published in Nature Climate Change.

The scientists used a sophisticated high-resolution model to simulate high rainfall and tropical cyclones (also called as hurricanes) to gain better insights into areas that could experience poor climatic conditions upon integrating solar geoengineering with the reductions in emission. This kind of model has been used for the first time to investigate the potential effect of solar geoengineering.

The research team examined water availability, temperature and precipitation extremes, and a measure of the intensity of tropical storms. They discovered that reducing warming by half using solar geoengineering cools the entire planet and decreases the changes in water availability and extreme precipitation in several places, as well as offsets over 85% of the increase in the hurricane intensity.

According to this model, less than 0.5% of the land would be influenced by the impacts of worse climate change.

The places where solar geoengineering exacerbates climate change were those that saw the least climate change to begin with. Previous work had assumed that solar geoengineering would inevitably lead to winners and losers with some regions suffering greater harms; our work challenges this assumption. We find a large reduction in climate risk overall without significantly greater risks to any region.

Peter Irvine, Study Lead Author, Postdoctoral Research Fellow, Harvard SEAS.

The scientists smartly indicated that this is a simplified method, which presumed two-fold carbon dioxide concentrations and represented solar geoengineering by reversing the sunlight. However, this method plays a key role in gaining insights into the use of solar geoengineering in tandem with other tools to limit the worsening impacts of climate change.

For years, geoengineering has focused on compensating for greenhouse gas induced warming without worrying too much about other quantities like rainfall and storms. This study shows that a more modest engineered reduction in global warming can lead to better outcomes for the climate as a whole.

Kerry Emanuel, Study Co-Author, Cecil & Ida Green Professor of Atmospheric Science, MIT.

The analogy is not perfect but solar geoengineering is a little like a drug which treats high blood pressure. An overdose would be harmful, but a well-chosen dose could reduce your risks. Of course, it's better to not have high blood pressure in the first place but once you have it, along with making healthier lifestyle choices, it's worth considering treatments that could lower your risks.

Peter Irvine, Study Lead Author, Postdoctoral Research Fellow, Harvard SEAS.

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