Greenhouse Gasses Declining Globally, But In U.S., Air Pollution Not Down As Much

Los Angeles April 6, 2020 Photo: @MikeSington, Twitter

A study published yesterday in the journal Nature Climate Change found that greenhouse gas emissions are down by 17% globally compared to 2019 levels thanks to strict coronavirus lockdowns, which could result in as much as a 7% decline in emissions for the year.  At the same time, an analysis by National Public Radio (NPR) looked at five years of air pollution data and found that despite a drastic reduction in automobiles on the road of 40%, ozone pollution has only decreased on average 7% nationwide.

Why This Matters:  We need to reduce greenhouse gas emissions by 4-7% each year globally for the foreseeable future to keep global temperature increases in check.  But we know these decreases in emissions will not last once we return to “normal” levels of activity.  What the U.S. air pollution data tells us is instructive for needed future policy changes.  Reducing pollution from automobiles will only get us so far — we must also get pollution from power plants, trucks, buses, and ships under control.  But the virus lockdowns have also shown us that even small decreases in smog make an appreciable difference.

Greenhouse Gas Emissions Declines

Greenhouse gas emissions prior to the pandemic had crept up over the last decade — we have not seen this kind of sustained reduction in the past, but the warming trajectory will not change significantly if we only have a decrease this year.  The study looked at the lockdown measures in 69 countries that are responsible for 97 percent of global carbon dioxide emissions — they examined in detail how six key economic sectors, including industrial activities, ground transportation, and air travel, changed from January through April. Interestingly, they found that the biggest reduction in greenhouse gas emissions globally came from transportation — reduced traffic from cars, buses, and trucks, while emissions from industrial activities only fell by 19 percent.  The study’s authors said that the results show the magnitude of the challenge ahead of us on climate change — to continue to reduce emissions this much while resuming economic activity.

Air Pollution Declines

The NPR team examined “more than half a million air pollution measurements reported to the EPA from more than 900 air monitoring sites around the country” comparing “the median ozone levels detected this spring with levels found during the comparable period over the past five years.”  This closer look at the data showed that in the vast majority of the U.S., “ozone pollution decreased by 15% or less, a clear indication that improving air quality will take much more than cleaning up tailpipes of passenger cars.”  Indeed, in some areas, they found that ozone pollution barely decreased even though those cities experienced traffic reductions of more than 40%.  In fact, the authors concluded that even though cars have gotten cleaner, they’ve become a relatively smaller source of pollution, and now trucks and buses are the largest sources of nitrogen oxides, which are one of the ingredients in smog.

To Go Deeper: You can hear Monica’s interview from yesterday’s Kojo Nnamdi show here.

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