Try to imagine an alternate history where we emerged from the industrial revolution with effective, sustainable fusion and solar power without ever polluting the planet.
First off, what we can or cannot imagine has absolutely nothing to do with what is or is not real, so it isn't clear why you're bringing this up. Three hundred years of knowing what is real through publicly testing ideas by systematic observation, controlled experiment and Bayesian inference had demonstrated that the pre-scientific "method" of "imagining what might be the case and then reasoning from it" is a hiding to nowhere, knowledge-wise.
That said, as it happens I can imagine such an alternative history. One simple way of doing it is to have an intelligent species that evolved somewhat more quickly than we did on a planet formed in very short order after the supernova that birthed it exploded. Such a planet would have a good deal more 235U in the mix, making light-water moderated natural uranium nuclear reactors possible (of the kind that existed on Earth in at least one location 2 billion years ago).
An intelligent species on such a planet would likely never go down the hydro-carbon-fuels path, but would be all-nuclear, all-the-time from a very early stage of technological development (one presumes that in such an environment they would be evolved for somewhat higher radiation-tolerance than most terrestrial species.) As such, no hydrocarbon pollution would be evident.
Now, to be clear, I am not saying any of this is true. Merely that I can imagine it. There are quite possibly any number of subtle issues that make such a scenario impossible, and the failure of philosophy (knowing by imaging) tells us that we will be very hard-pressed to find them. But you asked for an imagining, and there one is.