A study published yesterday (April 13) in the journal Nature Communications shows countries that have signed the Paris Climate Accord must reduce their carbon emissions much sooner than anticipated to reach the agreement’s goal.

Meeting that goal means that fossil fuels should make up less than a quarter of global energy production by 2100 when they currently power the world’s energy almost entirely. The study, by researchers at the International Institute for Applied Systems Analysis, shows that this shift needs to happen “well before 2040,” according to a press release, which individual countries aren’t on track to accomplish.

“This study gives a broad accounting of the carbon dioxide in our atmosphere, where it comes from and where it goes,” said World Bank consultant Brian Walsh, who led the study, in the press release. “We take into account not just emissions from fossil fuels, but also agriculture, land use, food production, bioenergy, and carbon uptake by natural ecosystems.”

Even if countries took on a “high renewable” energy plan where wind, solar and bioenergy increase production by five percent a year, global average temperatures would rise to 2.5 degrees Celsius, the study states. That is below the agreement’s ideal target of 1.5 degrees Celsius with its max target being 2 degrees Celsius.

There would be a chance to stay below that temperature if governments implement “substantial negative emissions technologies” like carbon capture and storage, but researchers just began studying such technology in the past 10 years.

Walsh is optimistic in the press release:

Walsh notes that the high-renewable energy scenario is ambitious, but not impossible—global production of renewable energy grew 2.6% between 2013 and 2014, according to the IEA. In contrast, the study finds that continued reliance on fossil fuels (with growth rates of renewables between 2% and 3% per year), would cause carbon emissions to peak only at the end of the century, causing an estimated 3.5°C global temperature rise by 2100.

The Trump administration hasn’t been clear whether it will stick with the agreement, but EPA Admin Scott Pruitt said, in an interview with Fox and Friends yesterday, that the U.S. needs to “exit” the agreement. The administration’s current coal-first energy policies make the agreement a far reach.

(H/t InsideClimate News)