President Trump's administration quietly killed a NASA project that monitored whether countries were reducing their greenhouse gas emissions, stoking fears about efforts to decrease global emissions, Science magazine reported.

NASA spokesman Steve Cole told the magazine that the agency's Carbon Monitoring System was canceled due to "budget constraints and higher priorities within the science budget."

Congress has repeatedly blocked the Trump administration's proposed cuts to NASA's earth science budget - including the monitoring system. But, Cole said, Trump's new tax law didn't mention the project, enabling the administration to end it.

He added that existing grants using the system would be allowed to continue, but that no new research will be permitted.

Kelly Sims Gallagher, director of Tufts University's Center for International Environment and Resource Policy, told Science that canceling the project could threaten plans to use the Carbon Monitoring System to track whether countries are falling in line with emission reductions laid out in the Obama-era Paris climate agreement.

The deal, signed in 2015, by nearly 200 countries, aims to lower global carbon emissions. President Trump pulled the U.S. out of the Paris climate deal last year, a move that was condemned by several world leaders.

"If you cannot measure emissions reductions, you cannot be confident that countries are adhering to the agreement," she said.

David Jacob, a Harvard researcher whose work was supported by the project, told the magazine that NASA had been planning to launch several new observatories connected by the system in order to monitor carbon.

"It would be a total shame to wind [it] down," Jacob said.

Science reported that there are currently 65 projects using the system, many of which focus on carbon in forests and changes in tropical forests.

Several Trump administration websites have removed references to climate change, and Environmental Protection Agency Administration Scott Pruitt has moved to kill former President Obama's landmark climate change rule for power plants.