TRAVERSE CITY, Mich. -- Automakers hoping for some relief from the EPA's targeted fleet average of 54.5 mpg by 2025 may not get it.

Speaking here last week at the Center for Automotive Research's Management Briefing Seminars, Christopher Grundler, director of the EPA's Office of Transportation and Air Quality, made it clear the agency is in no mood to move backward.

He said the EPA is already thinking about what comes after 2025, and expressed confidence that automakers will reach the target.

He said the EPA believes dangerous climate changes will occur if greenhouse gas emissions are not reduced 80 percent by 2050 from today's levels.

"We are in the beginning stages of tackling one of the most challenging issues of our time, which is climate change," Grundler told the industry gathering. "This is a global environmental problem. It will require every country and every economic sector to take meaningful action."

That and other remarks by Grundler indicate the agency isn't inclined to flex on the 54.5 mpg target that automakers would have to meet by the 2025 model year.

Some in the auto industry are hoping for a break. A final decision is due April 1, 2018, in the agency's midterm review. Grundler said the EPA has three choices in determining the final standard for the years 2022 to 2025: Standards will remain the same, they will become less stringent or they will become more stringent.

Citing the EPA's "Technical Assessment Report" issued last month that addresses progress being made by automakers to improve fuel economy, Grundler said automakers are ahead of the agency's estimates on reducing CO2 levels and improving fuel economy.

He said the agency has invested record amounts of time and resources in creating the information the EPA will use to make its final decision.

Since the original 2025 targets were set in 2012, the mix of cars vs. trucks sold has shifted from nearly 50-50 to closer to 40-60 in favor of trucks, mostly because of cheaper gasoline.