Literally anything we do modifies the environment. We generally tend to define "reversion to nature" as being a good thing, e.g. things that allow ecosystems to function independent of our fiddlings.
I think that the primary contribution to "ecosystem change" is not actually fossil fuel use (e.g. CO2 emission), but land use. There is no Amazon if you cut it down, the Swedish wilderness isn't wild if you criss cross it with roads, the lakes aren't the same if you dam them for hydro, etc.
We can't exist as a species of seven billion individuals that each seek to exact some amount of change that sums to an enormous difference without changing the planet. Regardless of whether you think it's a good or a bad thing, it just is, we do things.
We could create a car that runs on water and has tyres made of biodegradable leaves and it still can't go anywhere without roads that cause wildlife corridors.