Then is anything clean? As wind and solar both have clear externalities in manufacturing and decommissioning...

Probably well burned wood and other biomass might qualify. Though that is quite complex thing to do at least with particulate emissions...

I have sometimes wondered if we could consider specific solar and wind energy sites as 100% clean if we could calculate their carbon costs and actively take actions to counter carbon release to at least that amount. E.g., if a 1 KM solar farm took 12 Tons of Carbon and 1 tree sequesters 25 Kilos of Carbon per year, then we could start a forest of 500 trees using the Miyawaki Method and keep it thriving.

I have come across messages stating that Trees sequester Carbon for now only to release it all eventually, but Trees provide much more. They provide oxygen, a habitat for animal and insect life, they cool down an area, help attract clouds for rain, hold together the ground soil to prevent erosion, etc.

We ought to be reforesting and afforesting land again to compensate for all the cover that we've lost. Ensuring forests would help carbon-offset the carbon-load required to set up Low Carbon energy sources for locations that need them.

Does hydro have drawbacks? Yes. They change ecosystems. In many cases the new ecosystems are less desirable from the human perspective, but the reservoirs and rivers that are changed are still plenty viable for all sorts of ecosystems and life. This is highly different from fossil fuels, which produce pollution, toxins, and directly contribute to all of the evils of climate change.

This makes them a rather unique class of dirty renewables.