A nationwide campaign to phase out heat-trapping superpollutants is forcing changes across industries that cool homes, schools and businesses. One air conditioning giant, Daikin Applied Americas, is retooling the product lines for its three manufacturing plants in Minnesota.

"It is the single largest strategic move we have going on right now," said Philip Johnston, general manager of Daikin Applied's environmental business development center in Plymouth. "You have to touch every product, rather substantially."

Chemicals once developed as part of an environmental solution are now being ushered out in the United States, the latest step in the escalating fight against climate change.

Most people remember the compounds that were eating a giant hole in the Earth's ozone layer: chlorofluorocarbons and other substances used for refrigeration, air conditioning and aerosol sprays. Those chemicals have been mostly banned or phased out. But the ones developed to replace them, hydrofluorocarbons, or HFCs, are particularly powerful greenhouse gases, posing such a serious threat to the planet that the nations of the world have agreed to phase them down, too.

Hydrofluorocarbons are thousands of times more powerful than carbon dioxide at trapping heat in the atmosphere. The lifeblood of air conditioning and refrigeration, HFCs are one of the fastest-growing greenhouse gases, in part because rising temperatures are expanding demand for cooling.

Companies on the forefront in Minnesota and across the country are working to replace high-impact HFCs with lower-impact version of the man-made chemicals, or natural refrigerants.

In 2020, Congress passed a bipartisan bill to reduce the use of HFCs in the United States by 85% over the next 15 years, by 2036. That's consistent with the Kigali Amendment to the Montreal Protocol, which the U.S. ratified earlier this month in another bipartisan move.

It's a major climate strategy that could cut global temperatures up to 0.5 degrees Celsius by the end of the century, according to the U.S. Environmental Protection Agency (EPA).

The HFC phase-down clock in the United States starting ticking in January with a 10% cut this year. The cuts are to come via specific allowances the EPA grants to HFC producers and importers. People won't be required to replace appliances.

There's plenty of debate about what constitutes a "low impact" HFC, and a strong push to ditch the synthetic refrigerants altogether in favor of natural ones with nearly zero climate impact. Individual refrigerants are assigned "global warming potential" (GWP) ratings that compare effects of a refrigerant over time to the effects from the same amount of carbon dioxide. Carbon dioxide is rated one. Most natural refrigerants are near zero. Synthetic HFCs can exceed 12,500.

Environmentalists praise the industry-led move to lower-impact refrigerants, although some say the transition is slow and replacing one HFC with another is not the ultimate solution.

"I call this sort of the treadmill of fluorochemicals," said Avipsa Mahapatra, climate campaign lead at the Washington-based nonprofit Environmental Investigation Agency, which has campaigned against HFCs for years. "We are gradually ending our reliance on HFCs."

The refrigerants are hidden, sealed in pipes and equipment, but they are everywhere: car AC systems, supermarket coolers, the boxy HVAC equipment perched atop buildings, the refrigerators and air conditioners in people's homes. They're in a range of other products too, such as insulating foams, blowing agents and cleaning solvents. Emissions escape during operation and when equipment is junked.

Minnesota's new Climate Action Framework does not mention HFCs. The Minnesota Pollution Control Agency said it figured that the new federal regulations and industry leadership will deal with the issue. Environmentalists say the HFC phase-down is a rare bright spot in an otherwise very dark climate emergency.

"It's a really good success story in climate change," said J. Drake Hamilton, senior director for science policy at the St. Paul-based nonprofit Fresh Energy.

But it's not the transition that many say is needed, a total replacement of synthetic refrigerants with natural ones: water, ammonia, propane, isobutane and carbon dioxide itself. They're not perfect. Ammonia is toxic and propane flammable, for example, so products must be designed to protect for that.

Many manufacturers of U.S. household refrigerators are moving to propane or lower-impact HFCs, said Stephen Yurek, president of the Arlington, Va.-based Air-Conditioning, Heating, and Refrigeration Institute. Until now, one of the most common coolants in refrigerators (R-134a) has a climate-impact rating of 1,430, versus 3 for propane.

Everidge, which makes walk-in refrigerators and freezers and is based in Plymouth, has debuted a blast chiller that uses propane for grocers to rapidly cool hot food. Sales are promising, said Everidge executive vice president Eric Wickberg.

Natural refrigerants are more challenging to use in home air conditioning, Yurek said. That's partly because U.S. building codes prohibit installing a flammable refrigerant in an occupied space, he said. Building codes, he said, are the single largest hurdle in the transition.

"Right now at this time in the U.S. the likelihood of widespread use of natural refrigerants in comfort cooling is relatively low," Yurek said.

Shopping for climate-smart household appliances is difficult, for now. Labels typically display the type of refrigerant used but not its global warming potential rating. Consumers can look up ratings for products with the EPA's Energy Star label at the Energy Star Product Finder. There are other guides, such as the Environmental Investigation Agency's HFC-free refrigerator buying guide. The group also tracks HFC-free supermarkets.

Trane Technologies, owner of Thermo King in Bloomington, rolled out a fleet of refrigerated trucks and trailers this year that reduces the climate threat by nearly half.

"More and more we have customers that want the low global-warming potential refrigerants because they have their own climate commitments," said Randy Newton, vice president of engineering at Trane Technologies.

As for Daikin Applied, it decided to switch refrigerants two years ago. It's in the middle of replacing a hydrofluorocarbon with a global warming potential of 1,890 with another HFC, called R-32, that's nearly two-thirds less destructive. The switch will affect all three of its manufacturing plants in Minnesota, two in Faribault and one in Owatonna.

Inside the company's cavernous technology lab in Plymouth, technicians have been testing commercial rooftop units with R-32. The first "Rebel" units will start shipping from Minnesota next fall. For now, the large metal HVAC boxes hum inside the lab's big numbered test rooms designed to mimic rooftop environments, with big swings in temperature and humidity.

R-32 requires a slightly different compression technology and other equipment modifications, said Jason Dow, the technology center's manager. It is mildly flammable so systems have to protect for that. So far, he said, the change-out has gone smoothly.

R-32 is actually on the EPA's list of 18 HFCs being phased down, but the agency deems it acceptable for residential and light commercial air conditioning and heat pumps. The regulator is expected to approve it soon for certain chillers used in large commercial buildings, too, Johnston said.

"That's why it's called a phase-down, not a phase-out," Johnston said.

The EPA said it doesn't require a specific timeline for individual HFCs and is flexible on which ones are used, even those being phased down.

"EPA understands that these are transitions, and that manufacturers may move to other, even lower-GWP refrigerants over time as new alternatives become available," said EPA spokeswoman Shayla Powell.

Some environmentalists say the urgency of the climate crisis demands faster, more dramatic change. Mahapatra called Daikin's switch to R-32 "suboptimal."

"It would be absolutely foolhardy for any company sector or government to really choose to lock themselves in to a refrigerant that has several hundreds of times more impact on our climate compared to carbon dioxide," Mahapatra said.

Johnston acknowledged Daikin might have to change refrigerants again in the future. Other parts of the Daikin operation are exploring natural refrigerants, he said, but in his view they are difficult to use in common HVAC systems. Said Johnston: "We are encouraging our R&D centers to at least be evaluating other refrigerants."

Correction: Previous versions of the story misstated the timing of the rollout of Trane’s new refrigerated fleet.