In a paper published in Nature Sustainability, experts write that while zero-emission steel is within reach, it will require a big trade-off in production capacity.

Most modern steelmaking requires coke, a coal byproduct that fuels the furnaces used to transform iron ore into steel. As a result, it’s a major source of emissions. But although zero-emission steel is needed to mitigate human-caused climate change, the authors say it’s still unclear whether that goal is attainable, and how future climate policies and manufacturing processes would affect supply.

As an example, the researchers cited Japan, which has committed to zero emissions by 2050. But the strict carbon budget that will require could reduce steel production dramatically, they write, with the amount of high-quality steel available for automobile production reaching just 40 percent of current levels and crude steel production reaching 35 percent of current levels.

The industry will need abundant electricity, hydrogen and scrap to produce net-zero steel, the authors write.

The steel industry is working on solutions. According to the Leadership Group for Industry Transition, at least 73 green steel projects are in progress. But the researchers say the technology just isn’t there yet.

“These technologies still face serious technical, economic, and social challenges, and have yet to be implemented at scale,” said Takuma Watari, a researcher at the National Institute for Environmental Studies in Japan and the paper’s first author, in a news release. It’s still unclear whether enough electricity will be available in the future to power these innovations, he said.

Better processes for recycling steel scraps into high-quality materials are needed, the researchers write. They call for partnerships between the steel industry and users in a variety of sectors. But the current system “is incompatible with a zero-emission future,” they write.