Emissions of carbon dioxide – the greenhouse gas most responsible for global warming – reached an all-time high in 2018, scientists announced Wednesday.

Global carbon dioxide levels in our atmosphere "are now higher than they’ve been for millions of years," said Rob Jackson of the Global Carbon Project and Stanford University, one of the study's co-authors.

The emissions rose for a second year after little to no growth from 2014 to 2016. The increase in global carbon emissions, the largest jump in seven years, puts the goals from the landmark Paris Agreement in jeopardy.

“We thought, perhaps hoped, emissions had peaked a few years ago,” Jackson said in a statement. “After two years of renewed growth, that was wishful thinking.”

The United States, which had been steadily decreasing its carbon pollution, showed a significant rise in emissions for the first time since 2013.

The burning of fossil fuels such as coal, oil and gas releases greenhouse gases such as carbon dioxide and methane into Earth's atmosphere and oceans. The extra CO2 caused temperatures to rise to levels that cannot be explained by natural factors, scientists report. In the past 20 years, the world's temperature has risen about two-thirds of a degree Fahrenheit, the National Oceanic and Atmospheric Administration said.

Fossil fuels account for 81 percent of the world's energy use, despite the rise in renewable energy sources.

According to the study, global carbon dioxide emissions from fossil fuel sources – about 90 percent of all emissions from human activities – will reach a record high of more than 37 billion tons in 2018, an increase of 2.7 percent over emissions output in 2017.

“Emissions need to peak and rapidly decrease to address climate change," said Corinne Le Quere of the University of East Anglia. "With this year’s growth in emissions, it looks like the peak is not yet in sight.

“To limit global warming to the Paris Agreement goal of 1.5 degrees Celsius, CO2 emissions would need to decline by 50 percent by 2030 and reach net zero by around 2050," she said. "We are a long way from this and much more needs to be done, because if countries stick to the commitments they have already made, we are on track to see 3 degrees Celsius of global warming."

More:Global carbon emissions rose in 2017, dimming hopes to rein in climate change

More:UN says 2018 will be Earth's 4th-warmest year on record

The Global Carbon Project, which spearheaded the report, is an international scientific collaboration of academics, governments and industry that tracks greenhouse gas emissions.

The record high of carbon emissions in 2018 was driven by a solid growth in coal use for the second year in a row, along with sustained growth in oil and gas use. The planet’s five biggest emitters in 2018 are China, the USA, India, Russia and Japan.

This year, the amount of carbon dioxide in the atmosphere reached its highest level in recorded history, at 410 parts per million. CO2 levels were about 280 parts per million before the Industrial Revolution in the late 1800s.

The study was published simultaneously Wednesday in the journals Nature, Earth System Science Data and Environmental Research Letters.

Contributing: The Associated Press