Air quality declines as climate change accelerates

This is evidenced by the latest WMO Bulletin on air quality and climate

The expected increase in the frequency, intensity and duration of heat waves and the associated increase in the number of forest fires this century are likely to worsen air quality, harming human health and ecosystems. The interaction between pollution and climate change will impose an additional “climate penalty” on hundreds of millions of people, according to a new report by the World Meteorological Organization (WMO).

The annual WMO Air Quality and Climate Bulletin reports on the state of air quality and its close links to climate change. The bulletin discusses a set of possible air quality outcomes under high and low greenhouse gas emissions scenarios.

The WMO Air Quality and Climate Bulletin 2022 focuses particularly on the consequences of wildfire smoke in 2021. As in 2020, high temperatures and dry weather conditions exacerbated the spread of wildfires in western North America and Siberia, resulting in a widespread increase in levels of small suspended particles (PM2.5), which constitute a health hazard.

“As the planet’s temperature rises, wildfires and related air pollution are projected to increase, even in a low-emissions scenario. In addition to the consequences for human health, this situation will also affect ecosystems, as air pollutants are deposited from the atmosphere on the Earth’s surface,” explained Professor Petteri Taalas, WMO Secretary-General.

“This has happened in the heatwaves that occurred in Europe and China this year when stable upper atmosphere conditions, sunlight and low wind speeds led to high levels of pollution,” Professor Taalas said.

“This is a foretaste of the future, as the frequency, intensity and duration of heatwaves are expected to increase further, which could further worsen air quality, a phenomenon called ‘climate sanction’,” he added.

“Climate sanction” refers specifically to the amplification effect of climate change on ground-level ozone production, which has a negative effect on the air we breathe. The regions with the strongest predicted climate sanction, mainly in Asia, are home to about a quarter of the world’s population. Climate change could exacerbate surface ozone pollution episodes, leading to detrimental health effects for hundreds of millions of people.

The WMO Air Quality and Climate Bulletin, the second in an annual series, and related animation on atmospheric deposition were published ahead of the International Day of Clean Air for Blue Sky, 7 September. This year’s theme, spearheaded by the United Nations Environment Programme, is The Air We Share, and focuses on the transboundary nature of air pollution, while underscoring the need for collective action.

The bulletin draws on input from experts from WMO’s Global Atmosphere Watch network, which monitors air quality and greenhouse gas concentrations and can thus quantify the effectiveness of policies designed to limit climate change and improve air quality.

Air quality and climate are interconnected because the chemical species that cause air quality degradation are generally emitted in conjunction with greenhouse gases. Therefore, changes in one inevitably produce changes in the other. The burning of fossil fuels (a major source of carbon dioxide (CO2)) also emits nitrogen oxide (NO), which can react with sunlight and result in the formation of ozone and nitrate aerosols.

Air quality, in turn, affects ecosystem health through atmospheric deposition, since air pollutants are deposited from the atmosphere on the Earth’s surface. The deposition of nitrogen, sulphur and ozone can have a negative effect on the services provided by natural ecosystems, such as clean water, biodiversity and carbon storage, as well as affect crop yields in agricultural systems.

Forest fires in 2021

The European Union’s Copernicus Atmospheric Monitoring Service measures global concentrations of particulate matter. Inhalation of PM2.5 (i.e. particles with a diameter of 2.5 micrometres or less) for prolonged periods constitutes a serious health hazard. Sources of these particles include emissions from burning fossil fuels, wildfires and windblown desert dust.

Heavy wildfires generated exceptionally high concentrations of PM2.5 in Siberia, Canada and the western United States in July and August 2021. PM2.5 concentrations in eastern Siberia reached levels never seen before, and were driven mainly by rising high temperatures and dry soil conditions.

The estimated total annual emissions in western North America were between the first five years of the period 2003-2021, with PM2.5 concentrations far exceeding the World Health Organization’s recommended limits.

Globally, observations of the total annual fired area show a downward trend over the past two decades, as a result of fewer tarnish and grassland fires (WMO Aerosol Bulletin 2021). However, on a continental scale, upward trends have been observed in some regions, for example, parts of western North America, the Amazon and Australia.

Future scenarios

The Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) includes scenarios on the evolution of air quality as temperatures rise in the twenty-first century. The report assessed that the likelihood of catastrophic wildfires, such as those observed in central Chile in 2017, Australia in 2019 or the western United States in 2020 and 2021, will increase by 40-60% by the end of this century under a high-emissions scenario. and between 30% and 50% in a low-emission scenario.

If greenhouse gas emissions remain high, and global temperatures rise 3°C above pre-industrial levels in the second half of the twenty-first century, surface ozone concentrations are expected to increase in severely polluted areas, especially in Asia. This includes an increase of 20% in Pakistan, northern India and Bangladesh, and 10% in eastern China. Most of the increase in ozone will be due to an increase in emissions from the burning of fossil fuels; However, about a fifth of this increase will be due to climate change, which will most likely materialize through the increased number of heat waves, which will intensify air pollution episodes. Therefore, heat waves, increasingly common due to climate change, are likely to continue to lead to air quality degradation.

A global scenario of carbon neutrality would limit future extreme ozone air pollution events. This is because measures to mitigate climate change by phasing out the burning of fossil fuels (carbon-based) will also eliminate most human-caused emissions of ozone precursor gases (in particular, nitrogen oxides (NOx), volatile organic compounds and methane).

Suspended particles, commonly referred to as aerosols, have complex characteristics, which can exert a cooling or warming effect on the atmosphere. High amounts of aerosols, and the resulting poor air quality, can cause the atmosphere to cool by reflecting sunlight back into space, or by absorbing sunlight into the atmosphere so that it never reaches the ground.

The IPCC notes that the low-carbon scenario will be associated with less warming in the short term, before the temperature decreases. This is because the effects of aerosol particle reduction (i.e. less sunlight reflected back into space) will be felt first, while temperature stabilization in response to reductions in carbon dioxide emissions will take longer. However, emissions of natural aerosols (e.g. dust and smoke from forest fires) are likely to increase in a warmer and drier environment due to desertification and droughts, and could negate some of the effects of human-related aerosol reductions.

A future world in a low-carbon scenario would also benefit from the reduced deposition of nitrogen and sulfur compounds from the atmosphere at the Earth’s surface, where they can harm ecosystems. The response of air quality and ecosystem health to proposed future emission reductions will be monitored by WMO stations around the world, which can quantify the effectiveness of policies aimed at limiting climate change and improving air quality. WMO will therefore continue to work with a wide range of partners, including the World Health Organization and the European Union’s Copernicus Atmosphere Monitoring Service, to monitor and mitigate impacts.

Source: CSR Commitment