Poem: "To Hear the Falling of the Trees"

Both, sequentially. First the artificial heat creates a tropical indoor climate such that invasive pests like cockroaches -- which ordinarily die in freezing conditions -- can gain a foothold where they otherwise would not be able to survive. Then an urban heat island develops, where towns or cities are constantly warmer than the surrounding countryside; a combination of building materials that are heat sinks (stone, brick) and of active heat sources (wood, coal). Burning lots of carbon-based fuels while deforesting large tracts of land is what eventually builds up to global warming and other aspects of climate change.

And in a steampunk setting, it happens before science has advanced far enough to predict those problems ahead of time. Not that anyone in power would be likely to listen, but they aren't even going to get as much warning as we had. All they're getting is observation from people who, being closer to the land at that age of the world, start noticing the early changes like shifts in what grows when and where, the shrinking forests, etc. Plus the observed effects on humans, like blacklung from coal dust. It's harder to articulate these as major widespread issues, rather than personal issues, if the scientific infrastructure is just putting up its framework and hasn't even got the stairs laid yet.