Impact of solar geoengineering on temperature-attributable mortality

[Geoengineering News]

https://www.pnas.org/doi/10.1073/pnas.2401801121

Authors

Anthony Harding, Gabriel A. Vecchi, Wenchang Yang, and David W. Keith

December 17, 2024

https://doi.org/10.1073/pnas.2401801121

Significance

Solar geoengineering (SG) can cool the climate—the hard question is how its risks compare with its benefits? Using climate model simulations of idealized SG and data-driven of temperature-attributable mortality, we estimate that, in a world 2.5 °C warmer than preindustrial, 1 °C of global-average cooling by SG reduces mortality by over 400,000 deaths annually by 2080, with a possible range from −1.2 million to 2.7 million deaths annually. Mortality decreases in many hot, poor regions and increases in some cold, rich regions. We estimate the mortality benefits of reducing temperatures outweigh risks from air pollution and from ozone loss by 13 times for our central estimates, with a 61% probability the benefits exceed the risks. Uncertainty remains significant, highlighting the need for further research on SG’s trade-offs.

Abstract

Decisions about solar geoengineering (SG) entail risk–risk tradeoffs between the direct risks of SG and SG’s ability to reduce climate risks. Quantitative comparisons between these risks are needed to inform public policy. We evaluate idealized SG’s effectiveness in reducing deaths from warming using two climate models and an econometric analysis of temperature-attributable mortality. We find SG’s impact on temperature-attributable mortality is uneven with decreases for hotter, poorer regions and increases in cooler, richer regions. Relative to no SG, global mortality is reduced by over 400,000 deaths annually [90% CI: (−1.2 million,2.7 million)] for cooling of 1 °C from 2.5 °C above preindustrial in 2080. We find no evidence that mortality reduction achieved by SG is smaller than the reduction from equivalent cooling by emissions reductions. Combining our estimates with existing estimates of sulphate aerosol injection direct mortality risk from air quality and UV-attributable cancer enables the first quantitative risk-risk comparison of SG. We estimate with 61% probability that the mortality benefits of cooling outweigh these direct SG risks. We find the benefits outweigh these risks by 13 times for our central estimates, or 4 deaths per 100,000 per 1 °C per year [90% CI: (−11,23)]. This is not a comprehensive evaluation of the risk–risk tradeoffs around SG, yet by comparing some of the most consequential impacts on human welfare it is a useful first step. While these findings are robust to a variety of alternative assumptions, considerable uncertainties remain and require further investigation.

Source: PNAS

[Renaud de RICHTER]

phys.org /news/2024-12-solar-geoengineering-year.html

Solar geoengineering could save 400,000 lives a year

Michael Pearson 23/12/2024

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Regional mortality rate impact with income growth and climate adaptation. Credit: Proceedings of the National Academy of Sciences (2024). DOI: 10.1073/pnas.2401801121

When it comes to finding solutions to climate change, there's no shortage of technologies vying for attention, from renewable energy to electric vehicles to nuclear energy. One such contender, solar geoengineering, is favored by proponents who say it could quickly cool the planet and give the world time to fully implement efforts to limit emissions and remove carbon from the atmosphere.

But that promise comes with risks, which include potentially poorer air quality or depleted atmospheric ozone—both of which can cause serious health issues of their own.

A new Georgia Tech School of Public Policy-led study published in the Proceedings of the National Academy of Sciences suggests that while those risks deserve further consideration, solar geoengineering could save as many as 400,000 lives a year through a reduction in temperature-related deaths attributable to climate change.

"An important question is how the reduction in climate risks from solar geoengineering compares to the additional risks its use entails," said lead author Anthony Harding of the School of Public Policy.

"This study offers a first step in quantifying the risks and benefits of solar geoengineering and shows that, for the risks we considered, the potential to save lives outweighs the direct risks,"

Harding co-authored the PNAS article with Gabriel Vecchi and Wenchang Yang of Princeton University and David Keith from the University of Chicago.

The researchers studied a climate change mitigation strategy called stratospheric aerosol injection (SAI), a type of solar geoengineering that involves spraying tiny reflective particles into the upper atmosphere. Those particles would then redirect some sunlight back to space and help cool Earth.

The authors used computer models and historical data on how temperature affects death rates to see how much solar geoengineering might affect death rates, assuming a 2.5-degree Celsius increase in average temperature from pre-industrial levels and similar approaches to climate change as seen in the world currently.

They found that cooling global temperatures by 1 degree Celsius with solar geoengineering would save 400,000 lives each year, outweighing deaths caused by solar geoengineering's direct health risks from air pollution and ozone depletion by a factor of 13. This means that the number of lives saved due to solar geoengineering-caused cooling would be 13 times the number of lives potentially lost from solar geoengineering's known risks.

Many of those deaths would be avoided in hotter, poorer regions, the study notes. Cooler, wealthier regions could actually face increased cold-related deaths.

Solar geoengineering has generated millions of dollars in funding and a recommendation by the National Academies of Science that the federal government should provide millions more toward research and the development of a risk-risk analysis similar to what Harding's team produced. But the tech has also drawn concern, including from the Union of Concerned Scientists. That group says there's too much environmental, ethical, and geopolitical risk to proceed without much more research.

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The authors caution that their study is an important starting point in better understanding solar geoengineering's promise and peril but is far from a comprehensive evaluation of the technology's risks and benefits.

They say their models are based on idealized assumptions about aerosol distribution, population and income growth, and other factors. They also can't capture all of the real-world complexities that solar geoengineering would entail.

They note their study also does not address all of the potential risks of solar geoengineering, such as possible impacts on ecosystems, global politics, or the possibility governments will rely on the technology to delay politically difficult emissions cuts.

Still, the researchers say, the study suggests that for many regions, solar geoengineering could well be more effective at saving lives than emissions reductions alone and is worth keeping in the mix as the world searches for the optimal ways to cool our warming planet.

"There's no perfect resolution to the climate crisis," said Harding. "Solar geoengineering entails risks, but it could also alleviate real suffering, so we need to better understand how the risks compare to the benefits to inform any potential future decisions around the technology."

More information: Anthony Harding et al, Impact of solar geoengineering on temperature-attributable mortality, Proceedings of the National Academy of Sciences (2024). DOI: 10.1073/pnas.2401801121

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