An anticipated rise in the frequency, intensity and duration of heatwaves and an associated increase in wildfires this century is likely to worsen air quality, harming human health and ecosystems. The interaction between pollution and climate change will impose an additional “climate penalty” for hundreds of millions of people, according to a new report from the World Meteorological Organisation (WMO).
The annual WMO Air Quality and Climate Bulletin reports on the state of air quality and its close interlinkages with climate change. The bulletin explores a range of possible air quality outcomes under high and low greenhouse gas emission scenarios.
The WMO Air Quality and Climate Bulletin 2022 focuses in particular on the impact of wildfire smoke in 2021. As in 2020, hot and dry conditions exacerbated the spread of wildfires across western North America and Siberia, producing widespread increases in particulate small matter (PM2.5) levels harmful to health.
“As the globe warms, wildfires and associated air pollution are expected to increase, even under a low emissions scenario. In addition to human health impacts, this will also affect ecosystems as air pollutants settle from the atmosphere to Earth’s surface,” stated WMO Secretary-General, Prof. Petteri Taalas.
“We have seen this in the heatwaves in Europe and China this year when stable high atmospheric conditions, sunlight and low wind speeds were conducive to high pollution levels,” said Prof. Taalas.
“This is a foretaste of the future because we expect a further increase in the frequency, intensity and duration of heatwaves, which could lead to even worse air quality, a phenomenon known as the ‘climate penalty’,” he said.
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.
The Air Quality and Climate Bulletin, the second in an annual series, and an accompanying animation on atmospheric deposition, was published ahead of International Day of Clean Air for Blue Skies on Wednesday, September 7, 2022. The theme of this year’s event, spearheaded by the UN Environment Programme, is “The Air We Share“, focusing on the transboundary nature of air pollution and stressing the need for collective action.
The bulletin is based on input from experts in WMO’s Global Atmosphere Watch network which monitors air quality and greenhouse gas concentrations and so can quantify the efficacy of the policies designed to limit climate change and improve air quality.
Air quality and climate are 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.
Air quality in turn affects ecosystem health via atmospheric deposition (as air pollutants settle from the atmosphere to Earth’s surface). 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.
Wildfires in 2021
The European Union’s Copernicus Atmosphere Monitoring Service measures global particulate matter. PM2.5 (i.e. particulate matter with a diameter of 2.5 micrometers or smaller) is a severe health hazard if inhaled over long periods of time. Sources include emissions from fossil fuel combustion, wildfires and wind-blown desert dust.
Intense wildfires generated anomalously high PM2.5 concentrations in Siberia and Canada and the western USA in July and August 2021. PM2.5 concentrations in eastern Siberia reached levels not observed before, driven mainly by increasing high temperatures and dry soil conditions.
The annual total estimated emissions in Western North America ranked amongst the top five years of the period 2003 to 2021, with PM2.5 concentrations well above limits recommended by the World Health Organisation.
At the global scale, observations of the annual total burned area show a downward trend over the last two decades as a result of decreasing numbers of fires in savannas and grasslands (2021 WMO Aerosol Bulletin ). However, at continental scales, some regions are experiencing increasing trends, including parts of western North America, the Amazon and Australia.
Future scenarios
The Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report (AR6) includes scenarios on the evolution of air quality as temperatures increase in the 21st century. It has assessed that the probability of catastrophic wildfire events – like those observed over central Chile in 2017, Australia 2019 or the western United States in 2020 and 2021– is likely to increase by 40-60% by the end of this century under a high emission scenario, and by 30-50% under a low emission scenario.
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 realised 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.
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).
Particulate matter, commonly referred to as aerosols, have complex characteristics which can either cool or warm the atmosphere. High aerosol amounts – and thus poor air quality – can cool the atmosphere by reflecting sunlight back to space, or by absorbing sunlight in the atmosphere so that it never reaches the ground.
The IPCC suggests that the low-carbon scenario will be associated with a small, short-term warming prior to temperature decreases. This is because the effects of reducing aerosol particles, i.e. less sunlight reflected into space, will be felt first, while the temperature stabilisation in response to reductions in carbon dioxide emissions will take longer.
However, natural aerosol emissions (e.g., dust, wildfire smoke) are likely to increase in a warmer, drier environment due to desertification and drought conditions, and may cancel out some of the effects of the reductions in aerosols related to human activities.
A future world that follows a low-carbon emissions scenario would also benefit from reduced deposition of nitrogen and sulphur compounds from the atmosphere to the Earth’s surface, where they can damage ecosystems. The response of air quality and ecosystem health to proposed future emissions reductions will be monitored by WMO stations around the world, which can quantify the efficacy of the policies designed to limit climate change and improve air quality.
WMO will therefore continue to work with a wide range of partners including the World Health Organisation and the EU’s Copernicus Atmospheric Monitoring Service to monitor and mitigate the impacts.
