Climate Change and Air Quality

Climate change and air pollution share a lot of chemistry. Burning fossil fuels emits both CO2 and the precursors of PM2.5 and ozone. Warming, in turn, changes how those pollutants form, move, and persist. Researchers now describe the feedback between the two as the "climate penalty" on air quality.

Background

The climate-air quality link runs in three directions.

First, both problems share sources: power plants, vehicles, industrial boilers, and residential combustion emit greenhouse gases alongside NOx, SO2, VOCs, and particulate matter. Cutting fossil fuel use cuts both at once.

Second, climate change alters atmospheric chemistry. Warmer temperatures speed up the photochemical reactions that produce ground-level ozone from NOx and VOCs. Higher temperatures also increase biogenic VOC emissions from plants (especially isoprene from oaks and other broadleaf trees), which adds more fuel to the ozone reaction.

Third, climate change reshapes the physical conditions that determine air quality: stagnation events, drought, wildfire frequency, and the height of the planetary boundary layer.

What the studies found

The ozone climate penalty. A 2022 multi-model analysis in Environmental Research Letters using the CMIP6 climate models estimated that surface ozone increases by 0.2 to 2 parts per billion per degree Celsius of warming over polluted regions, even with the same precursor emissions. In remote, low-NOx regions the opposite happens (the climate "benefit," driven by more water vapor destroying ozone). The 2021 EPA Climate Change Indicators report similarly projects more ozone exceedance days in the eastern U.S. as temperatures rise.

Wildfires and PM2.5. A 2023 Nature paper by Marshall Burke and colleagues at Stanford showed wildfire smoke has erased roughly a quarter of the PM2.5 air quality progress made in the western U.S. over the past two decades. The 2024 Lancet Countdown reported that wildfire smoke was linked to a record 154,000 deaths globally in 2023.

Stagnation and heat waves. Studies by Loretta Mickley (Harvard) and colleagues using regional climate models project longer and more frequent atmospheric stagnation events over the U.S. Midwest and East as the jet stream weakens, trapping pollution near the surface. The 2003 European heat wave is the canonical example: combined heat and air pollution contributed to roughly 70,000 excess deaths, with ozone and PM2.5 each independently associated with a share of the toll.

Future health burden. A 2024 PNAS study by West, Fiore, and colleagues estimated that climate change could add 60,000 to 215,000 additional air-pollution deaths per year globally by 2050 under high-emissions scenarios, mostly from ozone and PM2.5 driven by warming, even before accounting for additional wildfire smoke.

Why it matters

The Inflation Reduction Act, EPA power plant rules, and most state climate plans were sold partly on co-benefits: cutting CO2 also cuts PM2.5 and ozone precursors, which prevents premature deaths now. EPA's 2024 power plant rule, for example, projected $370 billion in net benefits, with PM2.5 health benefits making up a substantial share.

The other direction matters too. If smoke and ozone keep rising with temperature, the regulatory tools the U.S. has used since 1970 (cap stationary sources, tighten tailpipe standards) will face diminishing returns. Adaptation tools (HEPA filtration in schools, smoke-aware HVAC, clean air shelters) become more important.

Open questions

How much of recent wildfire growth is climate-driven versus due to fuel buildup and land use is still debated, though most attribution studies place a substantial share on warming and drying. The interaction between climate change and indoor air quality (more time indoors during smoke events, longer cooling seasons, more residential HVAC use) is understudied. So is the regional fairness of climate-air quality effects: penalties fall hardest on already-hot, already-polluted regions.

Sources

• The 2024 report of the Lancet Countdown on health and climate change (Romanello et al., Lancet 2024)
• Climate change penalty and benefit on surface ozone: a global perspective based on CMIP6 earth system models (Zanis et al., ERL 2022)
• Estimating future climate change impacts on human mortality and crop yields via air pollution (West et al., PNAS 2024)
• The changing risk and burden of wildfire in the US (Burke et al., PNAS 2021)
• EPA Climate Change Indicators: Ozone and Climate Change
• Mortality during the 2003 heat wave in France (Fouillet et al., Int Arch Occup Environ Health 2006)
• Air quality co-benefits of carbon pricing in China (Li et al., Nature Climate Change 2018)