The interaction between pollution and climate change will impose an additional “climate penalty” for hundreds of millions of people, according to a new bulletin from the World Meteorological Organization (WMO).
The WMO Air Quality and Climate Bulletin reports annually on the state of air quality and its close interlinkages with climate change, reflecting on the geographical distribution of and changes in the levels of traditional pollutants under high and low greenhouse gas emission scenarios. As the globe warms, associated air pollution is also expected to increase, even under a low emissions scenario.
Ongoing climate change, caused by the accumulation of greenhouse gases in the atmosphere, is happening on a timescale of decades to centuries and is driving environmental changes worldwide. In contrast, the air pollution that occurs near the Earth’s surface happens on a timescale of days to weeks, and across spatial scales that range from local to regional.
Despite these wide‑ranging differences, air quality and climate change are strongly interconnected because the chemical species that lead to a degradation in air quality are normally co-emitted with greenhouse gases. Thus, changes in one inevitably cause changes in the other. The combustion of fossil fuels (a major source of carbon dioxide (CO2)) also emits nitrogen oxide (NO), which can react with sunlight to lead to the formation of ozone and nitrate aerosols.
According to the WMO, the “climate penalty” refers specifically to the climate change amplification effect on ground-level ozone production, which negatively impacts the air people breathe. The regions with the strongest projected climate penalty – mainly in Asia - are home to roughly one quarter of the world's population. Climate change could exacerbate surface ozone pollution episodes, leading to detrimental health impacts for hundreds of millions of people. Tiny, invisible particles of pollution penetrate deep into our lungs, bloodstream and bodies.
These pollutants are responsible for about one-third of deaths from stroke, chronic respiratory disease, and lung cancer, as well as one quarter of deaths from heart attack. Ground-level ozone, produced from the interaction of many different pollutants in sunlight, is also a cause of asthma and chronic respiratory illnesses.
Air quality affects ecosystem health via atmospheric deposition (as air pollutants settle from the atmosphere to Earth’s surface). Short-lived climate pollutants are among those pollutants most linked with both health effects and near-term warming of the planet.
They persist in the atmosphere for as little as a few days or up to a few decades, so reducing them can have an almost immediate health and climate benefits for those living in places where levels fall. Deposition of nitrogen, sulfur and ozone can negatively affect the services provided by natural ecosystems such as clean water, biodiversity, and carbon storage, and can impact crop yields in agricultural systems.
The Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report (AR6) also includes scenarios on the evolution of air quality as temperatures increase in the 21st century.
If greenhouse gas emissions remain high, such that global temperatures rise by 3° C from preindustrial levels by the second half of the 21st century, surface ozone levels are expected to increase across heavily polluted areas, particularly in Asia. This includes a 20% increase across Pakistan, northern India and Bangladesh, and 10% across eastern China.
Most of the ozone increase will be due to an increase in emissions from fossil fuel combustion, but roughly a fifth of this increase will be due to climate change, most likely realized through increased heatwaves, which amplify air pollution episodes. Therefore heatwaves, which are becoming increasingly common due to climate change, are likely to continue leading to a degradation in air quality. This climate change effect on ozone pollution is referred to as the "climate penalty". While the regions with the strongest projected climate penalty cover a relatively small proportion of the Earth’s surface, they are home to roughly one quarter of the world’s population, and therefore climate change could exacerbate ozone pollution episodes, leading to detrimental health impacts for hundreds of millions of people.
A worldwide carbon neutrality emissions scenario would limit the future occurrence of extreme ozone air pollution episodes. This is because efforts to mitigate climate change by eliminating the burning of fossil fuels (carbon-based) will also eliminate most human-caused emissions of ozone precursor gases (particularly nitrogen oxides (NOx), Volatile Organic Compounds and methane). A future world that follows a low-carbon emissions scenario would also benefit from reduced deposition of nitrogen and sulfur compounds from the atmosphere to the Earth’s surface, where they can damage ecosystems.
Policy changes that seek to improve air quality thus have repercussions on those policies that seek to limit climate change, and vice versa. For instance, a drastic reduction in fossil fuel combustion to reduce greenhouse. gas emissions will also reduce air pollutants associated with that activity, such as ozone and nitrate aerosols. Policies to reduce particulate matter pollution to protect human health may remove the cooling effect of sulfate aerosols or the warming effect of black carbon.
A better understanding of the multiple natural and anthropogenic sources of emissions and the meteorological influences on emissions and on the spread of the resulting pollution are critical for advancing our modelling of atmospheric composition and its changes. Long-term, consistent measurements enable the com- munity to understand how conditions have changed relative to the past and empower air quality and climate models to improve simulations of the atmosphere.
Climate change and associated poor air quality is a challenge in the context of sustainable development for all countries, in particular in cities and urban areas in developing countries, with levels of air pollution that are higher than the limits set out in the World Health Organization air quality guidelines. Society bears a high cost of climate change and air pollution due to the negative impacts on the economy, work productivity, healthcare costs and tourism, among others.
Some air pollutants, such as black carbon, methane and ground-level ozone, are also short-lived climate pollutants and are responsible for a significant portion of air pollution-related mortality and morbidity, as well as impacts on crops and hence food security, so their reduction has co-benefits for the climate. Hence, the economic benefits of investing in climate change and air pollution control cannot be overestimated, and it must be understood that there is also an economic rationale to act.
Writer: Tanvir Ahmad, Urban Planner; Climate Change & Public Health Researcher. Email: [email protected]
BDST: 1530 HRS, OCT 25, 2022