For decades the government pushed the notion that, to be healthy and slim, we needed to avoid fat and intake carbs. Decades and an entire epidemic of obesity before we are finally starting, only now, to realize how wrong they were.
Clean air ≠ Carbon dioxide reduction. The science of climate change, and all the incredibly complex measurements, studies, and theories about the effects, boils down to a single theory. Carbon dioxide is a greenhouse gas of small impact, but it increases the major greenhouse gas (water vapor) such that we are seeing and will continue to see a temperature runaway directly caused by humans increasing the CO2.
There is all sorts of research showing that the Earth is warming. Granted a lot of that research is not nearly as concrete as the narrative would have you believe. Take a look at the satellite data and compare it to the theory. Digging into the various generations of temperature records and seeing how lopsided the adjustments are is another eye-opening chore.
But even if you take the historical temperature data, as presented by the proponents of the theory at face value, the most critical component, that mankind has caused it, is dependent entirely on a theory of carbon dioxide that is not supported by the long-range historical data (ice ages during periods of much higher CO2), and is almost impossible to test on any sort of scale that would prove it one way or the other.
And on this shaky ground, the United States is supposed to reduce its carbon footprint in a manner that would utterly devastate our economy, and only have a single digit percent impact on the overall change in temperature. So even if you accept the temperature data at face value, and you accept the theory of carbon dioxide as an impactful greenhouse gas at face value, you also have to accept that the rest of the world, including the largest polluter (China), is going to follow our lead in a manner that will have an actual meaningful impact on the rate of warming.
That's a terrible bet, and the billions and trillions of dollars that we put towards this endeavor are much better spent on protecting forests, cleaning the plastic island out of the ocean, reducing known pollutants from being put into the atmosphere (like the smog plague of the 70s), defending endangered species, or any other number of measurable and worthwhile environmental endeavors.
That's the short version.