For the last few years, global carbon dioxide emissions have done something surprising—they haven’t really gone up. The most optimistic among us may have felt there was a change in the wind, but it was too early to call this the peak of our emissions. And in fact it wasn't, as the preliminary analysis for 2017 shows that emissions will once again tick upward.

Every year, a huge group of researchers publishes an analysis of the global carbon cycle, projecting the final tally for human emissions for the year based on data through September. At the same time, they make any necessary revisions to the numbers for previous years, based on new data or improved estimates. The team estimates not just the emissions from burning fossil fuels and other industrial activities, but from the other terms in the global equation, too. That includes the emissions caused by human land use changes (like deforestation) and the carbon absorbed and released by Earth’s land ecosystems and oceans.

Last year’s global human emissions projection for 2016, an increase of just 0.2 percent, held up when the final numbers came in. But the projection for 2017 shows an increase of 2.0 percent—a disappointing bump.

China has been the most important variable in this number ever since it surpassed the United States as the country with the highest emissions. That came during its explosive growth in the 2000s (though per capita emissions remain much lower than the US, which has about a quarter of China’s population). China’s massive economy and tight state control make its annual emissions pretty volatile. After slightly declining by about 0.3 percent last year, China’s emissions grew by 3.5 percent this year.

Despite canceling large numbers of planned coal power plants, China’s coal use rose three percent this year with larger increases from oil and natural gas. This was due partly to a burst of economic growth in the early part of 2017 (which has already slowed) and a dip in hydroelectric dam generation because of below-average precipitation. That means it is difficult to predict what China’s emissions will do in 2018.

The United States also slacked a bit, as last year’s 2.1 percent decrease in emissions gave way to an expected smaller 0.4 percent decrease for 2017. Higher natural gas prices drove down usage of that fuel a bit, with coal slightly increasing in response.

India’s emissions climbed 2.0 percent this year, which is actually considerably less than the 6.0 percent growth seen there in recent years. That, too, is likely due to short-term economic conditions. Emissions from European nations fell just 0.2 percent, which is less than usual. The combined emissions of all the nations not named China, India, or the United States grew by 1.9 percent.

In an editorial in the journal Environmental Research Letters, seven scientists write, “For the last three years, [emissions] were stable, despite continuing growth in the global economy. Many positive trends contributed to this unique hiatus, including reduced coal use in China and elsewhere, continuing gains in energy efficiency, and a boom in low-carbon renewables such as wind and solar. However, the temporary hiatus appears to have ended in 2017.”

While 2017’s numbers should not be read as a departure from nations’ emissions pledges made in the Paris Agreement, the researchers note that we’re drifting farther from the path that hits international goals. “At current annual rates of ∼41 [billion tons of] CO 2 for fossil fuels, industrial, and land-use emissions combined, time is running out on our ability to keep global average temperature increases below 2°C and, even more immediately, anything close to 1.5°C.”

Earth System Science Data Discussions, 2017. DOI: 10.5194/essd-2017-123

Environmental Research Letters, 2017. DOI: 10.1088/1748-9326/aa9662 (About DOIs).