In the United States alone, it’s estimated that the transportation sector produces 1.9 billion tons of carbon dioxide (CO2) annually. It’s no secret that CO2 contributes substantially to warming the planet, but it’s not the only climate-active material in the atmosphere: Emissions can have both warming and cooling effects depending on their chemistry and the timescale over which they are observed.
In a new study, Huang et al. model the total global climate impact of gasoline and diesel vehicle emissions as well as their impact on human health. Using the National Center for Atmospheric Research’s Community Earth System Model, a global chemistry‐climate model, along with emissions data from 2015, they calculate the net radiative effect of the gasoline and diesel sectors to be about +91 and +66 milliwatts per square meter, respectively, on a 20-year timescale. A laser pointer produces about 5 milliwatts, so emissions from the two sectors combined are heating the planet by roughly the same amount that shining 32 laser pointers on every square meter of the Earth would. Earth’s surface area is 510 trillion square meters, so that’s 1.6 quadrillion laser pointers.
The researchers broke down the overall heating into individual effects from different component compounds in vehicle emissions, focusing on two broad categories of emissions: short‐lived climate forcers (SLCFs), which include things like aerosols and ozone precursors, and long-lived greenhouse gases, with CO2 being the most prominent. SLCFs from gasoline and diesel vehicle fleets accounted for about 14 and 9 milliwatts per square meter, respectively, confirming that most radiative forcing comes from longer-lived emissions.
In terms of public health, the researchers calculate that the gasoline sector causes 115,000 premature deaths annually, whereas the diesel sector causes 122,100. The researchers attribute the deaths largely to exposure to smog (ozone) and soot (particles smaller than 2.5 micrometers). The scientists also analyzed how premature death rates varied regionally and proportionally with respect to the total distance driven in a region using each fuel type. These results showed large variability by region: In some places, there were relatively few premature deaths for the large distances driven on a given fuel type, whereas in others—most notably for diesel used in India—there were disproportionately high numbers of premature deaths. (GeoHealth, https://doi.org/10.1029/2019GH000240, 2020)
—David Shultz, Freelance Writer