According to New York Attorney General Barbara Underwood, the EPA purposefully misinterpreted an earlier court verdict. A judge had partly vacated the 2015-era HFC rules by saying that the agency didn't have the authority to make manufacturers switch away from HFCs when they had used HFCs to replace another ozone-harming material. The EPA, however, said it was wiping out the entire rule in response -- including a ban on using HFCs as replacements for ozone-hostile substances. Pruitt and crew are trying to strip away environmental rules "through the backdoor," according to Underwood.
The rule, instituted in 2015, was estimated to cut between 26 million to 31 million metric tons of greenhouse gases per year by 2020. If it manage 30 million metric tons, that would be equivalent to the yearly energy use of 3.2 million homes -- that would have a tangible effect.
Whether or not the lawsuit proves successful, the EPA's attempted rollback might have a limited effect. An international treaty scaling back the use of HFCs will take effect on January 1st, 2019. And the US' lack of participation might not matter. Companies selling products in most parts of the world aren't likely to switch back to HFCs for US versions just because they have the option, especially when there's no certainty that the reversal will last.