One Health Institute
Projecting Human Health Impacts:
Temperature Extremes Under Scenarios of Solar Climate Intervention
Extreme temperatures pose health risks to humans, animals, and the environment. Prior research has shown that areas experiencing extreme temperatures due to climate change show higher human mortality rates. CSU researchers explored a solar climate intervention scenario to create frameworks that have the potential to mitigate rising temperatures.
This Pilot Project aimed to understand the potential reduction of Earth’s warming by reflecting sunlight into space. Alongside carbon emission reduction strategies, researchers evaluated this approach’s potential impact on climate change.
The project analyzed temperature-related human mortality in adults aged 65+ across eight major U.S. cities using historical data to project the impact of strasospheric aerosol injection as a scenario with potential for decreasing rising temperatures. The project emphasized the need for ongoing research in specific population areas to counter rising temperatures.
Assessing midcentury temperature exposure scenarios, the project compared outcomes with and without stratospheric aerosol injection to estimate variations in temperature-associated human mortality. Additionally, it developed an adaptable framework for analyzing diverse health outcomes, climate scenarios, and geographical locations.
Who was the Research Team?
Atmospheric Sciences
James W. Hurrell
Lantao Sun
Environmental and Radiological Health
Brooke Anderson
David Rojas-Rueda
Daniel Dean
What is Solar Climate Intervention and what did they measure?
Solar climate intervention encompasses diverse methods aimed at cooling the Earth by reflecting solar radiation back into space. During the project’s funding period, researchers used a climate model to evaluate the effects of stratospheric aerosol injection (SAI) on climate, which is one possible form of solar climate intervention, compared to parallel climate change simulations without SAI. Researchers examined the output of climate model experiments that were designed to assess the climate impacts of SAI.
The goal of the SAI experiments was to avoid the escalating global temperatures that occur in the no-SAI simulations in response to increasing concentrations of greenhouse gases in the atmosphere. By hypothetically deploying stratospheric aerosol injection in 2035, researchers measured its impact on keeping global temperatures near the Paris Climate Agreement’s goal of 1.5C of warming.
What did they find?
Research indicated that SAI can reduce heat-related deaths by mitigating the impact of increasingly frequent extremely hot days due to climate change. However, it does not necessarily decrease the overall number of temperature-related deaths, as it does not offset the prevalence of cold-related fatalities, which are more common globally. This underscores the importance of further investigation into the complete impact of SAI on total temperature-related human mortality.
- Researchers identified varied associations between human mortality and temperature across cities, reflecting human adaptation to local conditions (e.g. warmer cities tended to have weaker mortality responses to heat, and higher “minimum mortality temperatures”, where the fewest temperature-related deaths occur, than cooler cities). This variability highlights the value of location-specific analysis, and of an adaptable pipeline that can be expanded to other diverse populations (especially internationally) to provide greater context for the global effects of SAI.
- The study predicted that by counteracting temperature escalations, SAI would successfully keep heat-associated mortality rates lower than under unmitigated climate change, especially in cooler northern cities. However, cold-associated mortality (which is more common than heat-associated mortality globally and in the study population) would also stay closer to current-day levels under SAI.
- In considering all temperatures (rather than just extremes) researchers found that even a few degrees over or under optimal temperatures stress the human immune system and can result in higher mortality rates at the population level.
- SAI’s effects on heat- and cold-associated mortality were roughly balanced, yielding generally similar total temperature-associated mortality rates between scenarios, although some cities did see definitively fewer or (more rarely) slightly more deaths under SAI compared to unmitigated climate change.
- Despite similar total numbers, the balance of cold- and heat-associated deaths would have important public health implications: adapting to the unprecedented level of heat-associated health burdens under unmitigated climate change would strain and require dramatic adaptations from medical and other support systems, while SAI would preserve more familiar conditions. Modeling city-level adaptations as dynamic (rather than fixed historical temperature-mortality associations) could be a valuable future step in this research framework.
