Besides, he's not advocating having more babies than we are now. He's saying that the idea that having less babies will solve climate change is a defeatist and unrealistic concept (whatever, I'm not agreeing or disagreeing with that), and that hey maybe we should just stop burning coal all day long, guys.
In isolation, yes -- and you're right that this represents a significant step forward. It does not, however, go far enough, and there are good reasons to make the perfect the enemy of the good here. Trump demonstrates many of them. As much as we might not want climate change, and in a broader sense the very ability to consider the scientific consensus when making policy, to be partisan issues, they will always be so simply because liberals want them and hurting liberals has gotten considerable conservative political currency, so we can expect any compromise solution to be overturned by the next batch of Republican elected officials simply because it's red meat for the base. Leaving the Paris accords, gutting the EPA, and mining national monuments all had other groups backing them, but "punking the libtardcuckflakes" was the easy way to sell the base on all of them. Stop using coal, and the next GOP President will campaign on bringing the poor coal miners back to work and besides, screw the libs. Invest in energy research, and the next GOP budget will forbid funding science entirely because it's time those ivory tower coastal liberals got a real job because hey, screw the libs.
There's a method to their madness, too: solving only part of this problem will make it worse for someone. We can't just stop mining coal without putting coal miners out of work, and not all of them can be or want to be retrained, so now the GOP gets to say that either we embrace the socialist babykilling elite snowflake welfare state or we reinvest in American jobs, so vote GOP and screw the libs. The same is true of trucking, air travel, livestock, and all the other industries that are killing the planet and also forming a key part of our economy. What this guy's plan is an attempt to do -- and, again, this is a common feature of all the Republican plans I've seen -- is to implement the most unpopular incremental steps with no attempt to compensate for them, so that they can then campaign on reversing it. After all, if this caused so much strife, imagine what a paradigm shift on the scale of our economy would do! Screw the libs!
In short, we know that the only way we're all going to get out of this mess is to fundamentally overhaul how we consume energy, which necessitates changing how we do business, too, and also how we approach wealth inequality. New technology does nothing if the 99% are too poor to make use of it, and economic incentives do nothing if the 1% can buy their way around them. Anything that falls short of that overhaul will be a politically toxic and ultimately unproductive incentive to swing the pendulum back the other way and screw the libs, and the GOP knows that.