Presumptive presidential nominee Donald Trump's speech about energy is sure to gladden the hearts of many automobile executives and engineers around the world -- not to mention investors in related stocks.

Speaking in North Dakota Thursday, Trump issued a strong signal that the anti-fossil-fuel policy that has been a Democratic Party talking point for more than a decade will be overturned if he is elected. While he didn't specifically mention regulations governing automobiles, he did promise to "cancel the Paris agreement" that commits most nations to fight climate change.

The reclassification of carbon dioxide as a pollutant, and the tightening of fuel-efficiency standards in California and by Democratic administrations and left-leaning backers, have forced the global auto industry to invest heavily in battery-powered electric cars, gas-electric hybrids and plug-in hybrids -- costly technology that has received mixed reviews by consumers.

If he were elected, Trump could immediately order the Department of Transportation to review fuel-efficiency standards with an eye toward relaxation. It's hard to see how that wouldn't be dandy for the equities of General Motors (GM) - Get Report , Ford (F) - Get Report , Fiat Chrysler Automobiles (FCAU) - Get Report and a slew of auto suppliers. (I wouldn't want to be long Tesla (TSLA) - Get Report on that day).

Early in his administration, President Obama proposed dramatically higher fuel-efficiency standards from the 27.5-mile-per-gallon-fleet average in place when he took office. By 2012, the administration announced a 54.5-mile-per-gallon standard that must be reached by 2025.

Automakers responded by equipping cars with smaller, less-powerful, more-fuel-efficient gasoline engines and adding to development budgets for electric vehicles, hybrids and related technologies. Executives nevertheless have said privately they're worried they won't be able to meet the 2025 deadline, at least not with vehicles that consumers will be enthusiastic about buying.

A decade ago, importing oil was seen as an enabler of burgeoning terrorism from foreign lands, especially in the Middle East. Saving fuel seemed like a patriotic thing to do, especially in light of U.S. casualties from the Iraq invasion. Today, the U.S. is a net energy exporter.

To make matters worse for advocates of stringent fuel-efficiency measures, energy markets have done an about-face. When crude oil and gasoline prices plummeted starting in mid-2014, car buyers began flocking to pickups, crossovers and other larger and less-fuel-efficient models. Sales of electric vehicles and hybrids lately have been weak, suggesting broad consumer skepticism and indifference to environmental arguments in favor of technologies purported to slowing, halting or reversing climate change.

Don't expect auto and oil executives to start wearing Trump for President pins, at least not right away. They're too practical to start taking sides publicly until they're sure of the outcome. Many, if not most, doubt or question the science behind claims that cars are a major culprit in climate change. I've heard them say it privately, but they'll never say so publicly. That's because politics, like climates, are always changing.

Doron Levin is the host of "In the Driver Seat," broadcast on SiriusXM Insight 121, Saturday at noon, encore Sunday at 9 a.m.

This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.