When the French government officially enacted a ban on short domestic flights this week, it hailed the measure as proof that France was at the vanguard of ambitious climate change policies. But critics say it’s much ado about almost nothing.

“We are the first to do it,” President Emmanuel Macron wrote in a celebratory message on Twitter, which also included a picture that said “Promise Kept” stamped in green ink.

At first glance, the promise would seem to have been kept: Any flight between two cities that can be replaced by a train ride of less than 2.5 hours is banned. In a country smaller than Texas and with an extensive high-speed rail network, that would appear to rule out a large number of domestic flights.

But appearances can be deceiving.

The decree formalizing the ban, which was published on Tuesday, is riddled with exceptions.

It applies only to cities connected by direct train service running “several times a day” and enabling travelers to spend a minimum of eight hours at their destination.

It does not apply to connecting flights, and it carves out an exception for the Paris Roissy-Charles de Gaulle Airport, one of Europe’s busiest passenger hubs, so that air routes between Charles de Gaulle and other French cities will stand.

Finally, since a significant amount of the nation’s high-speed train traffic is routed through Paris, only a limited number of cities away from the capital have direct train service between each other that would satisfy the rules in the decree.

When all is said and done, only three routes are actually cut — those between Paris-Orly Airport and the cities of Nantes, Bordeaux and Lyon.

The exceptions are meant to ensure that train service between two cities is sufficiently robust before flights between those same destinations are outlawed. But for critics, the confusing jumble of conditions has made the measure largely toothless.

“All that fuss, for not that much,” said Geneviève Laferrère, who handles transportation issues for France Nature Environnement, a federation of environmental defense groups.

Ms. Laferrère acknowledged that the ban could have an “educational” impact, by further encouraging travelers to look at alternatives to flying. But she said the government had missed an opportunity to act more forcefully, adding, “There are so many constraints that the effectiveness is gone.”

The ban on short domestic flights was part of a wide-ranging law to tackle climate change that was passed in 2021 with the goal of lowering France’s greenhouse gas emissions. Mr. Macron’s government recently unveiled an accelerated road map to cut those by 50 percent by 2030, compared with 1990 levels.

The government insists the ban is an important move in that direction.

“This is an essential step and a strong symbol in our policy to reduce greenhouse gas emissions,” Clément Beaune, the French transportation minister, said of the flight ban, in a statement on Tuesday that trumpeted the measure as a “world first.”

Although the ban was only enacted this week, airlines had already been following it for several years. In 2020, during the Covid-19 pandemic, the government forced Air France to cut some routes in exchange for a financial aid package worth billions of euros; it then banned competitors from rushing in to fill the gap.

But the ban’s official implementation was delayed after the airline industry filed complaints with the European Commission, which gave its greenlight for the law in December. The ban will apply for at least three years, after which the French authorities will analyze its impact before taking any new steps.

Nicolas Paulissen, the executive director of the French Airport Union, said that the air transportation industry was satisfied by the ban’s limited impact but worried that it could set a precedent for harsher measures.

“Tackling domestic flights doesn’t fix the issue of air transport’s CO2 emissions,” Mr. Paulissen added.

In 2019, domestic flights accounted for only 4 percent of the French transportation industry’s CO2 emissions, according to official statistics.

And according to an analysis of civil aviation data by Le Monde, the three routes that will be cut account for only about 5,000 flights per year — less than 3 percent of the total number of annual domestic flights in France. The French authorities have acknowledged that cutting those three routes reduced emissions only by about 55,000 tons of CO2 per year.

Laurent Donceel, the acting managing director at Airlines For Europe, an industry lobbying group for Europe’s largest flagship and low-cost airlines, said on Wednesday that countries should focus on “tangible” goals, like sustainable aviation fuel and electric and hydrogen-powered aircraft. He noted that airlines have committed to reaching net-zero carbon emissions by 2050.

“Instead of pursuing tokenistic bans, governments need to throw their efforts into advancing these real, meaningful solutions,” Mr. Donceel said in a statement.

But Ms. Laferrère, of France Nature Environnement, said that the government also needed to make rail transportation more alluring, by helping the national railway company push ticket prices down and investing more in railway infrastructure.

Moreover, she said, if the ban on short-haul flights only encourages French airports to reallocate more takeoff slots to long-distance ones, “we aren’t going to be saving a whole lot of CO2.”