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Cars and trucks are America’s biggest climate problem for the 2nd year in a row

Overall emissions are falling, but not fast enough to hit international targets.

The all-new 2018 Ford Expedition SUV comes off the assembly line at the Ford Kentucky Truck Plant October 27, 2017, in Louisville.
Bill Pugliano/Getty Images
Umair Irfan is a correspondent at Vox writing about climate change, Covid-19, and energy policy. Irfan is also a regular contributor to the radio program Science Friday. Prior to Vox, he was a reporter for ClimateWire at E&E News.

The transportation sector is the largest source of carbon dioxide emissions in the US for the second year in a row, according to an analysis from the Rhodium Group published Wednesday.

Overall, greenhouse gas emissions from the energy sector in the United States fell by just under 1 percent in 2017. But this represents a slowdown from 2016 and is far short of what the country needs to do in order to meet its commitments under the Paris climate accord.

Shrinking electricity needs and growth in renewable energy helped drive the overall decline in emissions, but increasing travel has led transportation-related emissions to overtake those from power generators, as you can see in this chart:

Rhodium Group

Greenhouse gas emissions from the power sector have been falling since 2006, as the amount of power generated from coal and natural gas declined. That’s happened even though prices for both fuels were low and more natural gas generators were brought online:

Rhodium Group

Meanwhile, vehicle miles traveled by cars and trucks went up last year by 1.3 percent.

We’ve known for a while that getting emissions down from vehicles is a difficult problem. Even with the growth in electric cars and the arrival of electric trucks and buses, the vast majority of motor vehicles still use fossil fuels.

And while the power sector has swiftly been transitioning from coal to natural gas and renewables because they’ve become cheaper, the transition to cleaner fuels in vehicles is harder in part because there are so many individual units that would need to change. Low fuel prices are also incentivizing consumers to buy more gas-chugging SUVs and trucks — these light-duty vehicles made up 63 percent of US vehicle sales last year.

Nonetheless, US emissions are still trending downward. But the numbers are not dropping fast enough to meet international climate targets. The US committed to cutting its emissions 26 to 28 percent below 2005 levels by 2025 under the Paris climate agreement, but that would require reducing our total carbon dioxide output by 1.7 to 2 percent each year for the next eight years. From 2016 to 2017, the United States only managed to get it down by just under 1 percent.

Given President Trump’s announcement in June that he intends to withdraw the United States from the agreement, there’s little hope of hitting the target while he’s in office.

On the other hand, at a press conference Tuesday with Erna Solberg, the prime minister of Norway, Trump once again alluded to the possibility that he might change course:

You never know.