Democratic presidential candidate Joe Biden has stumbled badly in his opening gambit on climate change. Avoiding any reference to the hot-button Green New Deal that several of his competitors have endorsed, he instead boasts about trumpeting the perils of climate change as a U.S. senator in the 1980s. To young and even middle-aged Democratic voters, this sounds like ancient history.

When campaign aide Heather Zichal signaled that her boss would pursue a “middle ground” on climate change, Biden earned the full-throated disdain of progressive Democrats who view global warming as a looming catastrophe, not an incremental annoyance.

If Biden really wants the “middle of the road” label to stick, he should continue singing the praises of the Obama administration’s automotive fuel economy reforms. The halfway measures introduced by Obama in 2012 did little more than perpetuate and, in some ways, weaken a corrosively compromised regulatory regime that has allowed gas-guzzling trucks and SUVs to dominate American auto sales.

Back in 1975, President Gerald Ford presided over the adoption of America’s first federal policy regulating the amount of fuel burned by U.S. motor vehicles. The original sin of these Corporate Average Fuel Economy, or “CAFE,” standards lay in the establishment of two separate thresholds for fuel efficiency — a more stringent one for conventional passenger cars, a weaker one for “light-duty trucks,” including pickups, vans, and other truck-like vehicles that generally used more fuel.

In the 1980s, the CAFE standard for cars seemed to be working. Conventional sedans, hatchbacks, and station wagons were still the norm, and many of those vehicle models became smaller, lighter, and more fuel-efficient.

Soon enough, though, the auto industry began to exploit the separate standard for light-duty trucks. By the early 1990s, what began as a trickle became a whole new generation of bigger, heavier vehicles that bore enough resemblance to trucks that they could evade the strictures of car-focused mileage standards. SUVs, once rare, became commonplace, minivans replaced station wagons, and pickups grew in popularity as versatile surrogates for passenger cars.

The Obama administration revamped the CAFE regime in 2012, for the first time pairing federal fuel economy standards with corresponding limits on carbon dioxide emissions. This sent an important policy signal that the carbon footprint of our automobiles is at least as consequential as their fuel consumption.

Obama’s reforms had their drawbacks, however. Not only did the preferential treatment of light trucks over cars persist, but vehicle size became the key factor driving both car and truck standards: the bigger a vehicle’s “footprint,” the more lenient the standard. This has given automakers a perverse incentive to concentrate their business on larger, more profitable vehicles that are subject to weaker fuel economy requirements.

Ford Motor Company has been clear in its navigation of our leaky fuel economy policies. In April 2018, its CEO revealed that the company would shift nearly 90 percent of its sales to trucks, SUVs and commercial vehicles by 2020. Dan Becker, a fuel economy expert at the nongovernmental Center for Auto Safety, told me: “With the new size-based standard, Ford can say, ‘All we are going to do is make F-150 trucks.’ As long as Ford meets the standard for the F-150 based on its footprint, that would be kosher.”

GM, too, is banking on higher profitability of its SUVs and trucks. Late last year, its CEO announced the idling of North American plants that had been assembling the compact Chevy Cruze, Buick LaCrosse sedan, and plug-in hybrid Volt.

If it wasn’t clear at the outset that our bifurcated fuel economy standards were fundamentally flawed, it’s unmistakable today. SUVs and other light trucks reaped a staggering 69 percent of all new auto sales in 2018, up from 51.2 percent in 2007.

We need rigorous, unitary standards that clamp down on carbon emissions and genuinely promote higher levels of automotive fuel economy. Candidate Biden may not be willing to insist that 100 percent of new car sales be all-electric by 2030 — a position taken by fellow Democratic presidential aspirant, Washington Gov. Jay Inslee. But will middle-of-the-road Joe, or any other Democrats in the lead, have the nerve to reform the fractures in our existing fuel economy regime?

Philip Warburg, a lawyer, writes about energy and environmental issues and is former president of New England’s Conservation Law Foundation.