Stratospheric Aerosol Geoengineering Could be Useful for Mitigating Climate Change

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The concept of stratospheric aerosol geoengineering involves adding a layer of aerosol particles to the upper atmosphere to decrease climate changes due to greenhouse gases like carbon dioxide.

Earlier studies demonstrated that solar geoengineering could be realized through aircraft technologies available in the market to deliver the particles at a cost of a few billion dollars annually and would decrease average temperatures worldwide.

But it is not clear whether this method could help decrease major climate hazards at a regional level. In other words, is it feasible to use it to minimize region-by-region changes in extreme temperatures or water availability?

The outcomes of a new study by scientists from UCL and Harvard indicate that even a crude technique, such as the injection of sulfur dioxide in the stratosphere, could mitigate several critical climate hazards without making the conditions of any areas worse.

The study results were recently reported in the Environmental Research Letters journal and use the findings of a complex simulation of stratospheric aerosol geoengineering to assess if the method could balance or worsen the impacts of climate change globally. Furthermore, a test was also carried out to find how these effects varied under different temperature scenarios.

The research group identified that reducing warming by 50% through the addition of aerosols to the stratosphere could bring down the major climate hazards virtually in all regions. The team observed worsening climate change effects only in a very small fraction of land regions.

Most studies focus on a scenario where solar geoengineering offsets all future warming. While this reduces overall climate change substantially, we show that in these simulations, it goes too far in some respects leading to about 9% of the land area experiencing greater climate change, i.e. seeing the effects of climate change exacerbated.

Peter Irvine, Study Lead Author and Professor, Earth Sciences, University College London

Irvine added, “However, if instead only half the warming is offset, then we find that stratospheric aerosol geoengineering could still reduce climate change overall but would only exacerbate change over 1.3% of the land area.”

The researchers highlighted the fact that solar geoengineering can treat only the symptoms of climate change and not the fundamental cause—the accumulation of CO2 and other greenhouse gases in the atmosphere. Therefore, this process should be examined as a complementary method for cutting emissions as an approach to handling climate change.

The research is a follow-up of a study reported last year in Nature Climate Change journal, which demonstrated similar results upon approximating solar geoengineering by simply turning down the sun. That study posed the following question: would the outcomes be positive with a more realistic simulation by injecting sulfur dioxide, the easiest known technique of solar geoengineering.

Our results suggest that when used at the right dose and alongside reductions in greenhouse gas emissions, stratospheric aerosol geoengineering could be useful for managing the impacts of climate change. However, there are still many uncertainties about the potential effects of stratospheric aerosol geoengineering and more research is needed to know if this idea is truly viable.

Peter Irvine, Study Lead Author and Professor, Earth Sciences, University College London

The researchers used the information from the Geoengineering Large Ensemble Study, which involved the use of an advanced climate-chemistry model to simulate the response of climate to a hypothetical deployment of stratospheric aerosol geoengineering.

In this model study, the team released sulfur dioxide at different latitudes in the Tropics to create a layer of aerosols that were tuned to maintain the temperatures steady under a severe global warming scenario.

The focus of the team was on changes in extreme precipitation, variations in extreme and mean temperature, and changes in water availability—the climate variables that govern the main climate risks.

Studies performed earlier indicated that stratospheric aerosol geoengineering could result in a significant weakening of monsoons and an intensification of drought.

But the authors identified that in those areas where warming was reduced by half using stratospheric aerosol geoengineering, the change was exacerbated, and it enhanced water availability and did not reduce it. This shows that concerns that stratospheric aerosol geoengineering could result in drought and aridification could be misguided.

Early research with climate models consistently shows that spatially uniform solar radiation modification could significantly reduce climate risks when combined with emissions cuts. But, should we trust the models? Uncertainties are deep and no single result is trustworthy, but this paper is a step towards more realistic modelling from injection to regional impacts.

David Keith, Study Co-Author and Professor, Engineering and Applied Sciences and Kennedy School, Harvard University

Currently, the group is investigating in detail the predicted effects of stratospheric aerosol geoengineering on the water cycle to understand the potential risks and benefits to ecosystems and society.


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