Global carbon dioxide emissions are on the rise again after three years of little to no growth, dashing hopes that they had peaked for good.

According to the latest report from the Global Carbon Project, a group of scientists who track the amount of carbon emitted by human activity, 2017 will see a 2 percent increase in the burning of fossil fuels, after nearly no growth in 2014, 2015 or 2016. Altogether, human-caused emissions this year are projected to reach 41 billion tons of carbon dioxide.

The findings, which have just been published in three separate scientific journals—Earth System Science DataEnvironmental Research Letters and Nature Climate Change—will also be presented today at the U.N. climate conference in Bonn, Germany. The work included data from a variety of sources, including national emissions inventories kept by the United Nations, global estimates of energy use and direct measurements of atmospheric CO2 concentrations, and involved dozens of authors from institutes around the world.

"It's quite difficult to say whether this year is a little glitch in a trajectory that is otherwise more or less flat, or whether this is resuming the emissions upward," said Corinne Le Quéré, director of the Tyndall Centre for Climate Change Research in the United Kingdom and lead author of the new report.

Three straight years of flat emissions had raised the question of whether the world's carbon output had finally peaked and would eventually begin to fall again. The new report now indicates that this may not be the case.

According to Le Quéré, an uptick in emissions is not necessarily that surprising—but the strength of the sudden growth is unexpected. And while 2017 hasn't ended yet and there's still a bit of uncertainty about the projections, Le Quéré noted that the last few years' projections have been accurate within about a half a percent or so.

"Two percent, if it gets realized, is really quite high, actually," she told E&E News. "And so that's really where the surprise is, is how strong this growth is after three years of stable emissions."

The reason for the increase, the report suggests, falls largely on China, whose 2017 emissions are projected to grow by about 3.5 percent, thanks to increases in the consumption of coal, oil and natural gas. India is also projected to see an increase in emissions by about 2 percent.

Despite an expected increase in coal consumption in the United States this year, domestic emissions are expected to have declined by about a half a percent this year. The European Union may also see a slight decline, although emissions throughout the rest of the world are also expected to have increased by about 2 percent.

Just last month, the World Meteorological Organization reported that atmospheric CO2 concentrations are still rising at an unprecedented pace, despite the plateau in emissions over the last few years (Climatewire, Oct. 31). That's because flat emissions aren't the same as no emissions—carbon dioxide was still being poured into the air between 2014 and 2016; the amount simply remained the same from one year to the next.

The WMO report noted that CO2 levels exceeded 403 parts per million in 2016, up from 400 ppm the previous year—a threshold scientists say hasn't been crossed in 800,000 years. This year, the Global Carbon Project report suggests, atmospheric CO2 levels may rise again by about 2.5 ppm.

One-off event?

It's unclear for now whether the renewed uptick in emissions will remain a trend.

"The growth in 2017 emissions is unwelcome news, but it is too early to say whether it is a one-off event on a way to a global peak in emissions, or the start of a new period with upward pressure on global emissions growth," said another of the report's authors, Glen Peters of the Center for International Climate Research in Oslo, Norway, in a statement.

He added that it can take extended periods of time—perhaps as long as 10 years or so—to confirm whether a trend is actually occurring or whether it's just a short-term fluctuation. Three years of no growth was not necessarily long enough to say that global emissions had definitely peaked, and one year of renewed growth doesn't necessarily mean that emissions will continue to rise after this year.

That said, the news comes at a time of great uncertainty over the future of global emissions reduction efforts, while nations around the world are convening in Germany for the U.N. climate conference. Just last week, Syria joined the Paris climate agreement, making the United States—the world's second-biggest emitter of greenhouse gases—the only nation whose commitment to the plan remains in question, after President Trump announced his intention to withdraw from the agreement earlier this year.

Experts are still questioning the extent to which Trump's promised Paris withdrawal, along with his systematic unraveling of other Obama-era climate and environmental policies, may affect domestic carbon emissions in the coming years. While the new report indicates U.S. emissions have slightly declined this year, Le Quéré suggested these policy shifts may actually be "very damaging" in the long term.

"If the U.S. does indeed move back towards coal—the U.S. is the second-biggest emitter—it is going to have an effect globally," she said. "Then it depends if the other countries follow, or if the other countries on the contrary take a different path, developing much more toward renewable energy."

Indeed, she said, the future trajectory of global emissions now depends largely on what happens in China, as well as in developing nations in Southeast Asia, in the Middle East and elsewhere around the world where emissions are still growing quickly in the background.

"So the political landscape is very, very critical at the moment, and there's really no time to be complacent," Le Quéré said. "People want to make a transition happen and want to address climate change. Now is the time to really establish policies in place and take action to make these trajectories change."

Reprinted from Climatewire with permission from E&E News. E&E provides daily coverage of essential energy and environmental news at www.eenews.net.