Burning carbon-based fuels releases carbon dioxide and other heat-trapping greenhouse gases into the atmosphere. It also produces tiny particles of sooty black carbon within the broader category often referred to as PM2.5 (for particulate matter below a certain size). These black carbon particles cause ground-level air pollution and also contribute to warming the atmosphere.

Greenhouse gases like carbon dioxide will stay in the atmosphere for decades, but black carbon particles only persist for days to weeks. So as California cuts back on use of carbon fuels, levels of black carbon should fall quite quickly, possibly yielding an early effect on climate. But just how big an effect could this be?

The state of California has a stated goal of reducing greenhouse gas emissions to 80 percent of 1990 levels. Researchers at UC Davis led by Michael Kleeman, Department of Civil and Environmental Engineering, used models to study the effect of this policy on long-lived and short-lived carbon pollutants. The models include weather and air quality effects of carbon emissions. The work was published recently in the Journal of Geophysical Research: Atmospheres.

Graphic of temperature changes in atmosphere

Temperature changes in the atmosphere over California from reducing airborne black carbon particles. The viewer is facing west, with southern California to the left of the figure. Credit Kumar et al, 2020.

They found that adopting low-carbon fuels in California reduces black carbon particles at ground level leading to improved air quality. But the changes to the concentrations of black carbon particles above the surface were minor, and so the particles did not have a significant impact on climate. The corresponding reduction in greenhouse gases has a much larger climate effect, lowering the surface temperature in California by 0.76 Kelvin in the year 2054.

The authors note that the changes caused by long-lived greenhouse gases are orders of magnitude larger than those caused by reducing short-lived black carbon particles.

“Adoption of low‐carbon energy will mostly affect climate in California through changes to long-lived as opposed to short-lived carbon pollutants,” they wrote.

Other authors on the paper are: Anikender Kumar, Christina Zapata, Chris Yang, Joan Ogden, Hsiang‐He Lee and Shu‐Hua Chen, all at UC Davis and Sonia Yeh, Chalmers University, Gothenburg, Sweden. The work was funded by the U.S. Environmental Protection Agency.

More information

Effects of Low‐Carbon Energy Adoption on Airborne Particulate Matter Concentrations With Feedbacks to Future Climate Over California (JGR Atmospheres)

Comparing Impacts of CO2 and Particle Emission Reductions (Eos Editor’s Highlights)


This article was originally published in the UC Davis Egghead blog on Nov. 17, 2020. 

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