The spending bill that Congress passed and President Trump signed Friday would extend and expand a tax credit supporting a long-elusive and expensive technology that captures carbon emissions from power plants and stores it underground.

The tax credit, created in 2008, was extended for 12 years, increasing the potential for broader deployment of carbon capture technology. The language expanding the credit was sponsored by Sens. Heidi Heitkamp, D-N.D., Shelley Moore Capito R-W.Va., Sheldon Whitehouse, D-R.I., and John Barrasso. R-Wyo.

It’s not clear what Trump means when he refers to “clean coal.” But he could be referring to coal plants that capture the carbon dioxide emitted from power plants and store it underground as a way of limiting its impact on global warming.

The carbon can be cooled and injected as a liquid underground. Some technologies can use the captured carbon for other energy uses.

For example, the Petra Nova plant outside Houston, America’s only successfully running carbon capture facility, sends the carbon dioxide by pipeline to nearby oil fields, where it is used to assist in the extraction of crude oil.

“The tax credit can be used for industrial and power use of carbon capture,” said Jeremy Harrell, policy director of ClearPath Foundation. “By lowering the benchmark of what the credit can be used for, it could allow investments in potentially the next Petra Nova plant, these first of a kind carbon projects for gas, industrial and coal use."

Technologies such as carbon capture and storage will be key to fulfilling the goal of the Paris climate change agreement to limit global warming to “well below” 2 degrees Celsius, or 3.6 degrees Fahrenheit, the limit at which many scientists say the world would see irreversible effects of climate change.

The United Nation’s scientific body determined in 2014 that if carbon capture isn't widely deployed, keeping global temperatures below the 2-degree Celsius threshold over the next century would be 138 percent more expensive.

A U.N. Environment Program report released last year found that to stay below 2 degrees Celsius, the world would have to close nearly every coal plant or outfit them to include carbon capture technology.

The concept has not been widely deployed, mostly because of the high cost to retrofit a coal plant for the technology. But advocates hope that changes now.

“I expect, and sincerely hope, that this bill will bring large investments into the carbon capture and carbon-to-value industries, which will help America meet its emissions reductions goals with more speed and less cost,” said Julio Friedmann, the CEO of Carbon Wrangler and former principal deputy assistant of the Energy Department’s Office of Fossil Energy.