Some corporations demonstrate strong concerns for the environment. And some swing with the political winds. Put General Motors in the latter category.

General Motors announced this week that it was dropping support of the Trump administration’s effort to strip California of its right to set vehicle fuel standards. And it said it would join President-elect Joe Biden’s push for auto electrification to reduce climate-warming emissions.

It was the right move. But pardon us if we’re not ready to trust the sincerity of GM CEO Mary Barra’s sudden, opportunistic reversal. It will take more than that to convince us that the nation’s largest auto manufacturer is as committed as Ford, Honda, BMW, Volkswagen and Volvo to tougher fuel standards.

This is the company American taxpayers saved from collapse with $9 billion in aid and tens of billions of dollars of loans after the Great Recession. In exchange, the company signed on to President Obama’s new fuel-efficiency standards.

But as soon as President Trump took office GM joined the new administration’s efforts to roll back those standards. Barra was a leader in that effort, meeting with Trump during his first weeks in office to encourage the reversal.

So Barra’s letter on Tuesday to environmental groups announcing it was flipping its position again rings hallow. Talk is cheap. Until the company demonstrates through its actions a solid commitment to tough fuel standards and a rapid switch to electric vehicles, Biden, environmentalists and Californians should be leery.

There are two issues at stake here.

First, in the spring Trump handed the oil and gas industry a big windfall by rolling back the Obama-era fuel regulations. The Obama rules required automakers to increase fuel efficiency across their fleets by 5% annually, reaching an average of 54 miles per gallon by 2025. The Trump rules rolled that back to 1.5% annually, with a target of 40 miles per gallon by 2026.

The move would lead to release of nearly a billion more tons of planet-warming carbon dioxide and the consumption of about 80 billion more gallons of gasoline over the lifetime of the vehicles built during the terms of the rule, the New York Times reported.

Second, the Trump administration issued rules stripping California and other states of their ability to impose tougher standards. California had a federal waiver under the 1970 Clean Air Act allowing it to set tougher standards than those of the nation. Twelve other states and Washington, D.C., had federal authority to follow California’s lead.

When California and other states sued to block the rules, the auto industry split, with GM, Toyota and Fiat Chrysler siding with Trump. Meanwhile, five other companies — Ford, Honda, BMW, Volkswagen and Volvo — cut a deal with California, agreeing to standards that are much closer to those set by the Obama administration than those in the Trump mandate.

For now, Toyota and Fiat Chrysler remain in Trump’s camp, while GM said Tuesday it would no longer defend in court the Trump rules undermining California authority. But Barra stopped short of embracing the agreement the state struck with the five other manufacturers.

Until she walks her talk, it will be hard to believe her company is seriously committed to saving the planet.