The DNR is standing by its environmental review of the Essar Steel project under construction in Nashwauk in the face of a legal challenge.
The group Minnesota Center for Environmental Advocacy is appealing an earlier court decision that approved the DNR's work.
MCEA says the DNR did not do enough to project the impact of the plant's carbon emissions on global warming.
The DNR's Steve Colvin said they did study the question, but science doesn't offer clear answers.
"It's beyond the state of the art to calculate the type of environmental effect those emissions might have on a global scale, or even changes to regional patterns," Colvin said.
Colvin said when the company applies for air permits, the Pollution Control Agency will consider global warming issues.
Essar Steel is the biggest of several projects on the Iron Range. It is expected to use 450 megawatts of electricity and to start turning out steel slabs by 2012.