[ricardo81]

I can't recall the source, IIRC it was EU research that looked at the lifetime carbon footprint of all energy sources. 'green' sources like wind and solar have a considerably lower footprint.

Which would make sense. At least in the UK, onshore and offshore wind are the cheapest sources going. Would suspect the amount of energy put into creating and maintaining them would mean that the LCOE is lower.

[pfdietz]

In a 100% renewable economy, where are the emissions coming from? Renewable sources don't create carbon atoms out of nothing. Cement production, maybe? Solar doesn't need cement!

If the economy is not yet close to 100% renewable, what matters is not small CO2 emission from making the renewable sources, it's how rapidly the remaining fossil sources can be displaced.

[ricardo81]

I'm not sure if there's such a thing as a 100% renewable economy, perhaps if you mean energy inputs yes, but there's always(?) going to be processes that involve emissions through 'work' as well as any emissions to create those renewable energy sources.

We can always offset. I mean, burning fossil fuels in itself is not a bad thing, but we know they're a finite resource and we simply have to offset those emissions with carbon sequestration.

[pfdietz]

Why shouldn't there be a 100% renewable economy? What energy inputs cannot even in principle be substituted for with renewable energy?

The reduction in fossil fuel usage needed to get to a climate-sustainable level is so large that any tolerable residuum could instead be handled by biomass.