The United States is the world’s second-biggest emitter of carbon dioxide and other greenhouse gases, which cause both ocean acidification and global warming. While the United States is responsible for about 14 percent of the world’s annual greenhouse-gas emissions today, it is the largest all-time source of cumulative carbon-dioxide pollution. And because it is the world’s largest consumer market, its energy system and federal policies play an outsize role in helping new technologies achieve mass scale and low cost.

Read: How coal country becomes solar country

The new report tells two different stories about emissions last year. The first—and far more upbeat—is that coal consumption is cratering. American coal use fell 18 percent, pulling down the power sector’s overall emissions by almost 10 percent. It was the largest one-year drop in coal consumption in history. “Coal ended the decade at less than half the level that it started the decade, which is remarkable,” Houser said.

As coal declined, the health of ordinary Americans improved. From 2005 to 2016, coal-plant shutdowns led to such significant air-quality improvements that they saved the lives of about 26,000 Americans, according to a separate study published this week in Nature Sustainability. (Data are not yet available to extrapolate those results to 2019.)

Jennifer Burney, the author of that study and an environmental scientist at UC San Diego, told me that whenever a coal plant closes, the statistical likelihood of death by any cause falls by “just shy of 1 percent” in any county within 15 miles. Infants and senior citizens see the greatest declines in mortality. Some of the worst toxic pollutants disappear from the air within days of a plant closure, she said. But carbon dioxide is, alas, not among them: It can linger in the atmosphere for hundreds of years, capturing heat and intensifying global warming all the while.

The switch from coal to natural gas has not been wholly good for American emissions. As utilities have adopted natural gas, they have created a vast and exceptionally leaky apparatus for moving it around the country. Some critics argue that this infrastructure is as bad for the climate as the coal system that it is replacing, because, in the shorter term, methane captures more heat in the atmosphere than carbon dioxide.

While there was a “meaningful increase in oil and gas methane emissions last year,” it was “not enough to offset the decline in coal generation entirely,” Houser said. About a third of the greenhouse-gas reductions from coal’s decline have been eaten by methane leaks and by outright pollution from burning natural gas, he said.

Net American Greenhouse-Gas Emissions by Sector, 2005–19

Data and chart: Rhodium Climate Service

The second story line from the Rhodium report is more pessimistic. Ultimately, the electricity sector generates only about 27 percent of national climate pollution. The remaining 73 percent of national emissions are produced by the rest of the economy, and these have barely budged. Almost nothing is being done about greenhouse gases from HVAC systems, 18-wheelers, or livestock, for instance.