Can we geoengineer a cooler planet to stop global warming?

Simulations show it could work...but with problems

Scientists studying ways to stop global warming have simulated the cooling effect of injecting sulfates high into the stratosphere similar to the planetary cooling after Mt. Pinatubo erupted in the Philippines, on 12 June 1991.
Scientists studying ways to stop global warming have simulated the cooling effect of injecting sulfates high into the stratosphere similar to the planetary cooling after Mt. Pinatubo erupted in the Philippines, on 12 June 1991.

What if particles were injected into the atmosphere and filtered sunlight to the point of reducing solar heating. Could this reduce global warming?

Geoengineering is a possible solution to combat climate change, but a recent study shows how such a manipulation is fraught with side effects.

First, look at a natural experiment during Australia’s largest bushfire in 2019 and 2020. The smoke blocked sunshine but the cooling results didn’t turn out for the better.

Almost 1 million metric tons of smoke rose into the stratosphere, causing it to warm nearly 2°F for six months and likely contributed to the large and persistent ozone hole that formed over Antarctica.

This data visualization shows the extent of the Antarctic ozone hole in September 2020. Massive Australian bushfires nine months earlier likely contributed to the large and persistent ozone hole that year. (Image: NOAA Climate.gov)

While the wildfire smoke blocked sunlight, it is full of sunlight absorbing black carbon particles which actually warmed up the surrounding air and didn’t produce a cooling effect on the lowest layer of the atmosphere.

It would take much more smoke to cool the troposphere than these fires injected, and that amount of smoke would have very large impacts on the upper atmosphere and ozone layer, according to researchers at NOAA’s Chemical Sciences and Global Monitoring Laboratories.

Other types of particles sent into the high parts of the atmosphere, or Stratosphere, may have different outcomes in reflecting sunlight to cool surface temperatures..

In contrast to fires, volcanic eruptions are known to block sunlight and not absorb a lot of solar energy. So could the sulfur particles be geoengineered to accomplish global cooling?

This is what researchers at the National Center for Atmospheric Research (NCAR) recently looked at using computer modeling to simulate sulfate aerosol injections into the stratosphere.

The results showed sulfate aerosols would largely mitigate the impacts of greenhouse gas-induced climate change but also resulted in unintended side effects in these simulations.

Illustration of proposed methods for climate intervention that would affect climate by modifying either incoming or outgoing solar radiation. (Graphic: Chelsea Thompson, NOAA / CIRES)

For example, while the simulations mitigated around two-thirds of expected winter warming trends due to climate change in Eurasia, a robust surface warming of nearly 3° Fahrenheit, still occurred every 30 years.

Another side effect identified in the simulations is less winter precipitation in the Mediterranean and a boost in summer moisture. The opposite would occur in Scandinavia – wetter winters and drier summers.

Lead author Antara Banerjee, a CIRES research scientist working at NOAA CSL, said that the model required enormous inputs of sulfur dioxide to mitigate the expected warming – as much as 50 million metric tons would need to be continuously injected into the stratosphere every year by the end of the century to obtain zero global-mean temperature change even as CO2 continues to increase.


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