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Artificially dimming the sun may reduce the risk of future droughts in Cape Town

Injecting tiny, reflective particles of sulphur dioxide into the upper atmosphere to artificially dim the sun could help reduce the likelihood of Day Zero-level droughts in Cape Town by up to 90% in the future.

This is according to the findings of a new research paper from the University of Cape Town, in collaboration with the Norwegian University of Science and Technology and the National Center for Atmospheric Research in the US, published in the journal Environmental Research Letters.

The authors assessed the potential impact of controversial solar radiation management (SRM) geo­engineering using stratospheric aerosols injection (SAI) to offset the risk of Day Zero-level droughts in a high-emission future using climate model simulations from the Stratospheric Aerosol Geoengineering Large Ensemble Project. 

According to the research team, if implemented, this would involve blocking a small amount of solar radiation from reaching the Earth’s surface by, for example, injecting reflective aerosols into the upper atmosphere to counteract rising temperatures.

“Our findings suggest that keeping the global mean temperature at 2020 levels through SAI would offset the projected end-century risk of Day Zero-level droughts by approximately 90%, keeping the risk of such droughts similar to today’s level,” the team writes in their paper. 

It describes how the Western Cape experienced extreme multi-year drought in 2015–2017, causing the most severe water shortage experienced by the province in more than a century.

“While Day Zero was avoided through a mix of drastic reductions in water usage (by nearly 50%) and short-term supply augmentation, the drought was termed the ‘new normal’, implying that climate change was acting to move the region towards semi-permanent drought-like conditions.”

However, in a December 2018 paper, science advocacy group Climate Analytics emphasised SRM is not a solution to the climate problem as it does not address the drivers of human-induced climate change and is a “potentially dangerous interference with the climate system”.

“SRM would strongly alter the climate system producing ‘winners’ and ‘losers’ in different regions and with different levels of deployment. It would, therefore, most likely become a source of a massive conflict between nations. If not banned altogether, it would put the power of triggering a climate shock into the hands of single actors,” reads that report.

SRM is one class of geoengineering and has its limits, including masking the warming effect of greenhouse gases.

“Our findings suggest that SRM could help to lower future risks of severe droughts in Cape Town,” lead author Dr Romaric C Odoulami of the African Climate and Development Initiative said in a statement. 

The findings must be seen in context, however. “A change of location, model, or SRM deployment design might produce significantly different results.”

The researchers stress such methods should not be viewed as an alternative to cutting emissions, and there are several “less risky” climate actions to help limit future Day Zero drought risk.

The study on SMR is part of a more comprehensive project through the Developing Country Impacts Modelling Analysis for SRM (Decimals) fund.

Earlier this year, studies funded by Decimals from South Africa and Benin found that SRM might be able to reduce the impacts of climate change across most regions of Africa, but not all.  

Another study found that parts of West Africa could be worse off if sun dimming were used to combat climate change, “underlining the fact that SRM is likely to be contested and highly controversial even if it can reduce climate change impacts for most people”.

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Sheree Bega
Sheree Bega is an environment reporter at the Mail & Guardian.

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