"The US was already off track in meeting its Paris Agreement targets. The gap is even wider headed into 2019."

That's the dire news from Rhodium Group, a research firm that released preliminary estimates of US carbon emissions in 2018. Though the Trump administration said it would exit the Paris Agreement in 2017, the US is still bound by the agreement to submit progress reports until 2020 . But the administration has justified regulatory rollbacks since then, claiming that regulation from the US government is unnecessary because emissions were trending downward anyway.

But it appears that emissions have increased 3.4 percent in 2018 across the US economy, the second-largest annual increase in 20 years, according to Rhodium Group's preliminary data. (2010, when the US started recovering from the recession, was the largest annual increase in the last two decades.)

This reversal of course—the first increase in emissions in three years—came from a few sources. Carbon emissions from the US electricity sector increased by 1.9 percent, largely because the installation of new natural gas plants has outpaced coal retirements. Cheap natural gas has been credited with killing coal, which is a dirtier fossil fuel in terms of emissions. But natural gas is a fossil fuel, too, and burning more natural gas than is needed to simply replace coal will result in more carbon emissions.

But electricity wasn't the main culprit. Transportation was.

"The transportation sector held its title as the largest source of US emissions for the third year running, as robust growth in demand for diesel and jet fuel offset a modest decline in gasoline consumption," Rhodium wrote.

Industrial emissions from various types of manufacturing as well as emissions from buildings both saw significant increases in their carbon emissions in 2018.

US consumers are demanding more

While the US federal government has largely abdicated its responsibility to deal with carbon emissions in a meaningful way, many states and utilities have deliberately moved away from the most carbon-intensive forms of electricity. So why are emissions from the sector going up? The Rhodium Group notes that, while in previous years US electricity demand declined or stayed flat, in 2018 that was not the case. To meet all that demand, natural gas plants have been running more, and energy companies are installing more new natural gas capacity.

"Natural gas-fired generation increased by 166 million kWh during the first 10 months of the year," Rhodium wrote. "That’s three times the decline in coal generation and four times the combined growth of wind and solar."

With transportation, the story is sort of similar. Passenger vehicles have received the most attention from policymakers, with electric vehicle rebates, fleet-purchasing agreements, and a legacy mandate to increase fuel economy (despite the Environmental Protection Agency's best efforts to roll back fuel economy standards put in place by the Obama administration). In 2018, gasoline demand decreased by just 0.1 percent. But growth in the US trucking industry increased diesel demand by 3.1 percent, and demand for air travel increased jet fuel demand by 3 percent.

While there have been movements to decarbonize trucking, either with electric trucks or with fuel-cell vehicles, electric semis are not currently widely available. Jet fuel is even more intractable, and most of the developments in that industry involve lower-carbon fuel synthesis.

Finally, Rhodium Group called the building and industrial sectors "the forgotten sectors," because they're so rarely targeted by policymakers and clean energy advocates. Emissions from the building sector often come from homes or buildings burning fuel oil and natural gas for heating and cooking. "We estimate that direct emissions from residential and commercial buildings... increased by 10 percent in 2018 to their highest level since 2004." Industry, too, from manufacturing and concrete-making, saw increases in emissions in 2018, largely due to strong economic growth and relatively little oversight from policymakers to curb carbon.

"Absent a significant change in policy or a major technological breakthrough, we expect the industrial sector to become an increasingly large share of US greenhouse gas (GHG) emission in the years ahead," Rhodium wrote.