Rising sea levels, worsening air quality, freak weather events, and biodiversity loss—what do they all have in common? Climate change.
Climate change is one of the biggest threats to humanity’s survival. Governments worldwide have taken steps to mitigate climate change, with the US and Europe showing a drastic improvement in air quality since 1980.
A study appearing in Earth’s Future projects that air quality in the US will decline as climate change progresses.
The study, led by Fernando Garcia Menendez, an Associate Professor at North Carolina State University, noted that ground-level ozone spikes could cause public health risks in the future. Dr. Menendez spoke to Interesting Engineering (IE) about the study.
Commenting on the issue of air pollution, he said, “Air pollution is one of the world’s leading causes of disease, and ozone pollution contributes significantly to this. Climate change may worsen it over areas with large populations, with consequences on public health.”
This piece looks into how air pollution will intensify due to climate change, drawing from the study’s findings, and discusses its implications for public health and policy.
Ozone and its dual role
The research focused on ground-level ozone as a way to study air pollution. Ozone is a gas that consists of three oxygen molecules. This element is present in the atmosphere of the Earth, found at ground level and high in the stratosphere.
Stratospheric ozone
In the stratosphere, the ozone layer protects us on Earth by absorbing the harmful ultraviolet (UV) radiation from the Sun. DNA damage caused by UV radiation in living organisms can result in a range of diseases, including cancer.
The chemical reactions between oxygen molecules and incoming UV light in the stratosphere lead to the natural production of ozone. When the UV hits the ozone molecules, it again decomposes to oxygen. Known as the ozone-oxygen cycle, this process helps maintain the ozone layer.
Due to human activities, the ozone layer has been depleted, largely as a result of chlorofluorocarbons (CFCs) emitted by older refrigeration and air conditioning systems.
Under the Montreal Protocol, CFCs have been phased out to protect and allow the recovery of the ozone layer. While the recovery is slow, it is still in progress.
Ground-level ozone
Ozone is a hazard closer to the Earth’s surface, in the troposphere. It leads to multiple health problems, impacts crops, and disrupts ecosystems.
This ozone forms due to a chemical reaction between volatile organic compounds and nitrogen oxides in the presence of sunlight. The sources of these compounds are mainly from industrial and vehicle emissions and power plants.
As temperatures soar due to climate change, the chemical reaction responsible for producing the ozone gas is accelerated. The European Geosciences Union reports that global ground-level ozone has risen by 2 to 12% each decade since 1995.
Therefore, it is important to gain a clearer understanding of how air pollution might be impacted moving forward.
Improved climate modeling
Previously, researchers have studied air pollution and how it would be affected by climate change. However, most studies relied on a single emission scenario, i.e., emissions are either increasing or reducing.
Similarly, many studies also focus on a single climate sensitivity value. Dr. Menendez explained, “Climate sensitivity determines the extent to which an increase in greenhouse gas concentrations will raise temperature and thus influence ozone concentrations.”
Without considering potential sensitivities, this approach restricts our understanding of the effects of varying levels on air pollution.
In light of these limitations, Prof. Menendez and his team utilized a combination of models to capture the various influences on ground-level ozone levels.
The team utilized a human activity model to analyze emissions under various economic and policy scenarios, an Earth system model to simulate climate change impacts, and a global atmospheric chemistry model to investigate how emissions influence ozone concentrations.
They examined three 30-year periods—representing the past (1981-2010), mid-century (2036-2065), and end-century (2086-2115)—to identify trends and project future ozone levels under varying climates and human influences.
To improve the reliability of their predictions regarding ozone pollution levels in vast geographical regions, they developed a new statistical technique for bias correction. And, they analyzed high ozone pollution events, which are the most harmful to public health.
The future looks ozone-rich
The study’s findings project that the peak ozone concentration seen once a year will increase by roughly two parts per billion by 2050. In other words, the worst days for ozone pollution will become more intense.
Additionally, higher climate sensitivity will result in these levels increasing to 4.5 parts per billion!
“We discovered that climate change has the potential to heighten both the frequency and severity of days with elevated ozone pollution in the US. This will make it more difficult to meet air quality standards and lead to more significant air pollution impacts compared to current climate conditions,” commented Dr. Menendez.
The influence of climate sensitivity was discovered to be as impactful as greenhouse gas emissions in mid-century projections. Under high climate sensitivity scenarios, extreme events become much more frequent and intense.
In low climate sensitivity scenarios, the effect of ozone pollution remains minimal, even with high emissions.
Dr. Menendez added, “While there is still uncertainty about the Earth’s climate sensitivity, our study finds that considering how the Earth will respond to greenhouse gas levels is critical when assessing climate-driven changes to air pollution frequency and magnitude, or other climate impacts.”
Under moderate scenarios, 8.5 million US residents could be living in areas non-compliant with air quality standards, with the number increasing to 13.5 million under high climate sensitivity scenarios.
Most US regions are witnessing a rise in ground-level ozone, especially in densely populated urban areas. Nevertheless, regions like the Gulf Coast and Southeast US demonstrate minor reductions in ozone levels as the century progresses.
What does this mean?
According to the US Environmental Protection Agency, the average ozone concentration over eight hours (a standard used in air quality measurements) has reduced by 21% since the 1990s.
An illustration showing the mechanism of the ozone layer depletion. Source: Dimitrios Karamitros/iStock.
Despite this, according to the projections of Prof. Menendez’s study, ozone pollution can worsen over the next decade. Serious consequences could arise from this, including a rise in premature deaths, respiratory diseases, hospital visits, and school absences.
“Increasing ozone levels will also undermine efforts to reduce air pollution through emissions controls and other policies,” added Prof. Menendez.
Climate change is a global effect observed across a large timescale, making issues such as air pollution hard to address.
Prof. Menendez expressed his opinion on regulatory challenges, saying, “Regulations used in the past to mitigate ozone pollution are not suited for this type of environmental impact. It will take a large and coordinated effort to address climate change and prevent its detrimental effects.”
One effective method for reducing ground-level ozone today is transitioning to renewable energy sources, given that fossil fuel plants are major contributors to ozone production.
Conclusion
The WHO has indicated that ground-level ozone is a serious health threat, causing 22,000 premature deaths annually in 25 European nations.
The projections made by the study point to a need to reevaluate our current policies surrounding the reduction of ground-level ozone and ensure that the future does not look as risky for humans.
There is some uncertainty surrounding these types of studies, particularly their predictions concerning Earth’s climate sensitivity. While this study is only restricted to regions in the US, it points to a global concern.
Dr. Menendez remarked on these uncertainties, saying, “We presented a new approach to project climate impacts on US ozone episodes and compared major sources of uncertainty in such projections.”
“Despite the uncertainties, the study finds that climate-induced increase in ozone pollution will likely raise pollution levels compared to current climate conditions and may increase the risk of not meeting air quality standards.”