Dimming – (no) protection for the polar ice sheets | Polarjournal
Solar eclipses are a natural form of dimming Earth. But it lasts only a few minutes, whereas the idea of an artificial dimming would be a rather long-term affair. (Photo: Michael Wenger)

In some parts of the world, the sun has been blazing down from the sky for months now, causing excessive heat waves. Those who can, seek out places that are cool and protected from the sun, such as behind darkened windows of a store or vehicle. A similar proposal, but on a global scale to quickly mitigate global warming, is under consideration: dimming Earth. A study is looking into this proposed solution, with ambivalent results.

Artificially increasing the amount of aerosols, i.e. gas particles, in the stratosphere and thus creating a kind of sunshade that dims Earth and protects it from solar radiation is something that Johannes Sutter, PhD, from the Oeschger Center for Climate Research (OCCR) and his colleagues have investigated in more detail. The researchers focused primarily on the effects on the West Antarctic Ice Sheet and found that such a dimming would only partially delay melting: Depending on how much carbon emissions were reduced globally, the longer the delay would be, buying time to take further action to mitigate climate change effects. But this dimming would not bring a stop. The researchers published their findings in the latest issue of the journal Nature Climate Change.

For their study, the researchers modeled the impact on the West Antarctic Ice Sheet, which is particularly protected from uncontrolled melting by the Thwaites Glacier as it holds back ice masses like a cork. (Photo: David Vaughan)

For their study, the team investigated the effects of a reduction in solar radiation on Antarctica and especially the West Antarctic Ice Sheet. They looked at different CO2 emission scenarios and modeled the behavior of the ice sheet and the Southern Ocean with and without dimming. The results of the modeling were sobering: under a “business as usual” scenario, dimming only reduces the rate of warming and melting. Only a combined application of CO2 reduction measures and dimming could possibly prevent a collapse of the ice sheet. True stabilization would most likely occur with a reduction of CO2 emissions to zero.

The result of the researchers’ worst-case climate change model calculations show that “geoengineering”-induced dimming (right) could reduce Antarctica’s surface temperature by slightly more than half compared to business as usual (center). But in the end, the delay would still be devastating for Antarctica and the ice loss would be enormous (gray areas). Graph: Sutter et al (2023) Nature Climate Change

The magic word that researchers have been studying is “geoengineering.” This refers to intervening artificially in various natural processes using technical methods to reduce the effects of climate change or prevent them from occurring in the first place. Advocates are concerned with preventing tipping points from being crossed and taking measures to reduce greenhouse gases in order to stabilize the climate in the long term. “The window of opportunity to limit global temperature increases to below 2 degrees is closing rapidly,” explains Dr. Sutter, an ice modeling specialist. “it is therefore possible that technical measures to influence the climate might be seriously considered in the future.”

This also includes measures to reduce the amount of solar radiation reaching Earth, the Solar Radiation Management SRM. This involves transporting and releasing gas particles into the stratosphere, which form a kind of artificial curtain due to their density and thus reduce the amount of energy that reaches the surface. One example of such aerosols is sulfur dioxide, which many will remember as the cause of acid rain in the 1980s.

Geoengineering would be another global experiment and a potentially dangerous human intervention in the climate system.

Prof. Thomas Stocker, University of Bern

And that’s where the trouble lies, as Sutter and his colleagues explain. On the one hand, millions of tons of aerosols have to be continuously transported into the stratosphere by aircraft every year, which will lead to massive CO2 emissions. On the other hand, the effects on natural processes and organisms on Earth from the dimming and aerosols have not been studied in detail, but are likely to be in the direction of acidification again. In addition, says co-author Professor Thomas Stocker, of the University of Bern, there is a risk that other climate protection measures would be suspended or prevented. He believes geoengineering should not be considered as a climate mitigation measure because “geoengineering would be another global experiment and a potentially dangerous human intervention in the climate system.”

Dr Michael Wenger, PolarJournal

Link to study: Sutter et al (2023) Nat Clim Chang, Climate intervention on a high-emissions pathway could delay but not prevent West Antarctic Ice Sheet demise; doi.org/10.1038/s41558-023-01738-w

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