Carbon Emissions Fell During Obama's Last Year in Office

But an even trickier problem than coal is emerging.

Kevin Lamarque / Reuters

If there’s one chart that sums up the state of the energy economy in Barack Obama’s last year in office—that captures the progress of the last few years and the pain of what’s to come—it might be this one:

U.S. Carbon Dioxide Emissions by Sector
Data is independently collected by the EIA. The y-axis is in million metric tons. (EIA)

Let’s explain why. Earlier this week, the U.S. Energy Information Administration, or EIA, released its research note on how greenhouse-gas emissions from the energy sector shifted in 2016. It’s among the last reports we’ll get about Obama’s final year in office, and as such it provides a baseline for Trump. Here’s how things were going when Obama handed the keys to Trump. For people who are interested in energy mostly because of its importance in the fight to mitigate climate change, the report brought both good and bad news.

The good is that the most important trend in energy continues, albeit slowly. In 2016, U.S. carbon-dioxide emissions from energy-related activities fell 1.7 percent. (“Energy-related activities” here includes not only what fuels are burned generating electricity, but also gas and diesel fuel for cars and trucks.)

The continued decline in CO2 emissions is driven by cheap natural gas, which is itself made possible by domestic fracking. For the second year in a row, carbon emissions from the power sector fell by nearly five percent.

The bad is that, as coal fades, some trickier problems are replacing it. As the chart shows, transportation—mostly, gasoline for cars and trucks—is now the biggest source of carbon-dioxide emissions in the United States. CO2 emissions from the transportation sector ticked up 1.9 percent in 2016. But transportation is different from power generation. The mix of electricity sources can be made more climate-friendly by swapping out coal for natural gas and renewables. But reducing emissions from cars and trucks will require less gasoline to be burned, period. So federal fuel-efficiency rules must either get more stringent or there must be a mass consumer move to electric vehicles.

These two factors combine to give the chart above, where CO2 from electric power is steadily falling, but emissions from transportation are slowly rising.

“I really do think that the transition to cleaner energy is underway,” said Carol Werner, the executive director of the Environmental and Energy Study Institute. “There are many factors influencing that, and while the Trump administration is seeking to halt a variety of regulations and policies, I think that there is embedded change. The genie is out of the bottle.”

Obama himself made a similar case in Science in January. “Putting near-term politics aside, the mounting economic and scientific evidence leave me confident that trends toward a clean-energy economy that have emerged during my presidency will continue,” he said.

But the rise in emissions from transportation belies this inevitability. As the price of gasoline falls, people want to drive more and they buy less fuel-efficient vehicles. “With lower gas prices, the sale of SUVs is up,” said Werner. “That is not good.”

These trends could all, of course, change in response to Trump administration policies. The EPA and Department of Transportation have already began to roll back Obama-era policies meant to nudge utilities toward toward building natural-gas, solar, and wind capacity. They have also announced that they will review federal fuel-efficiency standards for cars and light trucks. While these rules have little effect on the price of SUVs, they could lead to gas mileage decreasing nationwide.

The report doesn’t capture all U.S. greenhouse-gas emissions—like methane and hydrofluourocarbons—because some are released through agriculture and other kinds of land use. The government has not yet issued its estimate of total greenhouse-gas emissions for 2016.