Only a few short weeks ago, I rashly announced that the protracted arguments over the European Mobile Air Conditioning (MAC) Directive had been pretty much settled. I determined the twist and turns of claim and counterclaim between automaker Daimler, which thinks the low-GWP refrigerant R1234yf is a safety risk, and most of the rest of the car industry, which doesn't, was now at an end.

I am afraid I might have underestimated the stubbornness of the French.

The policymakers in the European Commission have made it clear they believe removing high-GWP (Global Warming Potential) refrigerants from usage is a key step in protecting the atmosphere — first came the MAC Directive for cars, and then last month the F-Gas regulations for stationary systems.

However, France's top administrative court appears to have now decided that a little bit of high-GWP gas is not a major problem to the planet's future. Of course, the Conseil d'Etat did not make this ruling in a vacuum; it did so in a hearing on whether Daimler was legally entitled to produce cars with the refrigerant R134a in them.

The Conseil said in a statement that the ban on the cars, originally imposed by France's ecology minister, was unjustified. The court agreed with Daimler's position that the vehicles "had not been shown to present a serious threat to the environment." It also determined the small percentage of the French car fleet that this applied to — the Mercedes Benz A, B and SLA class — was too small to pose a serious problem.

Previously, the French government had appeared to thumb its nose at the German automakers, by banning Mercedes sales in the first place. Now the French courts appear to be thumbing their collective nose at the European Commission.

The EC's scientific arm, the Joint Research Centre, had already ruled in March definitively (or so we thought) that R1234yf was safe for automotive use, and therefore there would be no reason under European law to continue using R134a. And, of course, in the U.S., the EPA has effectively accelerated the refrigerant's specification by offering automakers credits toward meeting greenhouse gas standards for its use.

Never mind that the Commission followed the March ruling with the announcement that it would start official proceedings against Daimler for shipping cars with noncompliant refrigerant in them — and, for good measure, initiating the same process against the countries that allowed registration of those noncompliant cars (take a shameful bow Belgium and the U.K.).

Never mind also that the GWP of R134a is 1430, whereas the GWP of R1234yf is less than 1, so switching to the HFO would make a major difference to greenhouse gas emissions.

No, for the French court, the principle was enough. In its view, Daimler should be given the green light to continue filling its cars with the high-GWP refrigerant. In the view of the EC, however, the Conseil is rewarding Daimler for flouting what is intended to be one of its flagship environmental regulations.

Given all the additional work that has now been done by the EC, I think we can safely say the safety of R1234yf has been established as beyond question — from everyone but Daimler at least.

No, this is more about the Conseil offering an incendiary challenge to the fabric of Europe's regulatory regime — pitting a long-established national judiciary against the much younger Commission. But it is not just about France's top administrative court touting at the power of Brussels, it is a strike at the heart of EC environmental policy, by seeming to suggest that use of a bit more high-GWP refrigerant is neither here nor there.

Where it leaves Daimler — I say with a definite sense of déjà vu — is still unclear. The automaker can continue selling the noncompliant cars in France, but it is currently theoretically still prevented from selling them elsewhere. With the automotive media now reporting that the German automaker's preferred alternative of CO2 refrigerant could be ready for 2017 production, Daimler could simply be hoping to ride out the storm for a bit longer, paying any fines that may be levied against it.

For its part, the EC must now be sweating over whether Daimler can use the French ruling as a test case for the rest of Europe. This may have started as a single automaker with concerns over a refrigerant, but it is now nothing less than a challenge to the validity of European environmental regulation.