Global carbon dioxide emissions remained flat for a third year in a row, yet far more powerful greenhouse gases “keep creeping up,” according to the annual report from the European Union and the Netherlands Environmental Assessment Agency.

The U.S., Russia, China and Japan decreased their CO2 output from 2015 to 2016, while the EU stayed flat and India’s emissions continued to increase. But emissions of methane and nitrous oxide have been increasing.

Methane molecules trap roughly 30 times more heat than carbon dioxide over a century, and the gas comes from agriculture, coal and gas production, and landfills. Nitrous oxide, known as laughing gas, trap about 300 times more heat than carbon dioxide; it’s emitted by soil fertilizers and chemical production.

Agricultural statistics are not updated as frequently as energy and industry-related numbers, so the report did not include complete data for those gases. But a preliminary assessment showed an upward trend in the U.S., China, Japan, India, Germany, the United Kingdom, France, Poland, Italy and Spain.

Nitrous oxide emissions could get much worse as a result of global warming. Arctic permafrost contains roughly 67 billion tons of the gas, and, as that ice layer thaws, up to one-fourth of the region could become a net emitter, according to a study published in July.

Joint Research Centre Despite a 2 percent decrease in the U.S. carbon footprint from 2015 to 2016, Americans still produce by far the largest amount of CO2 per capita.

Other studies indicate that methane in particular has surged over the past decade, increasing by 10 or more parts per billion annually in 2014 and 2015, up from 0.5 parts per billion on average in the early 2000s, according to a study published in December in the journal Environmental Research Letters.

“The leveling off we’ve seen in the last three years for carbon dioxide emissions is strikingly different from the recent rapid increase in methane,” Robert Jackson, a co-author of the paper and a professor of earth system science at Stanford University, told Phys.org. The results for methane “are worrisome but provide an immediate opportunity for mitigation that complements efforts for carbon dioxide.”

The study may not paint a full picture of total methane emissions. A paper published last month found that emissions from agriculture could be much larger than previously reported, due to reliance on out-of-data data on livestock.

The U.S. could be responsible for up to 60 percent of the global spike in human-caused atmospheric methane emissions since 2002, a Harvard University study found last year. The researchers said there was too little data to identify specific sources, but the increase tracked the boom in shale oil and gas production across the country, which leaks large amounts of methane from wells and pipelines.

In June, Environmental Protection Agency Administrator Scott Pruitt defended President Donald Trump’s decision to withdraw the U.S. from the Paris Agreement, a deal to slash carbon emissions. He insisted the country had nothing to apologize for, and suggested the U.S. could help other nations reduce their CO2 output with its natural gas technology, namely hydraulic fracturing, or fracking.

“If nations around the globe want to seek to learn from us on what we’re doing to reduce our CO2 footprint, we’re going to share that with them,” he said at a press conference, “and that’s something that should occur and will occur in the future.”

Pruitt, like the president, has said he doesn’t believe humans are the main cause of climate change.