These seem to be the two big camps on the Future and they both seem a little loopy to me.
Eternal Growthers seem to think that we can just trust the natural order of things to deliver us 3% growth forever regardless of what we plan, or in the most extreme cases, only if we don't make plans.
Sustainability folks lay claim to being the "realists" but to me they seem way off base in their presumption that we can plan to do anything for more than 20 years. Has this been the case in the last 20 years? The 20 before that? Was the earlier 20 more or less fast-changing? Wrongo.
So what's the "right" answer? I think it's in recognizing that we're surrounded by irreducible complexity but at the same time taking responsibility as the species most likely to be able to figure out what to do. We need to understand that nothing we recognize as "normal" is what the Earth was like before we showed up. And we need to start measuring and caring for the biosphere as if it were something we owned and wanted to keep working, even if we can't find the user's manual.
The Technium and the Biosphere probably can't be isolated from each other. But we can examine the places where they touch and try to make them function better. And we need to do so without scapegoating one another or inventing cheaply manipulative metanarratives to drive poorly-executed anti-growth plans. The problems are mostly hard. Here are a few that don't seem so hard (at least from the standpoint of whether they're the right thing to do), though, just so I'm offering some policy rather than merely pontificating on how we should all think smarter:
* Stop fishing, in as large an area as possible. The oceans are so fished out that you actually catch more fish when you cordon off most of the fishing areas and allow the seas to recover.
* Get Fusion working. One of the reasons Fusion is "always 20 years away" is that we keep cutting back funding because it's always 20 years away. We know it works because everything already runs on a centralized fusion reactor. We just need to technologize it.
* Fix recycling. I mean REAL recycling. Get all the value out of every atom we productize. Technologies like 3D printers are the near edge of the fabrication revolution, and harnessing them as recyclers could put the trash problem to bed, permanently.
* Higher density living. Cram people together into cities, bulldoze suburbia, plant forests.
And of course any one of these things changes the others. Get fusion working and electric cars proliferate on supercheap electricity made from sea water. Does that save Suburbia? Maybe information tech kills it first. Would higher density living accelerate or slow down the recycling systems? We just can't know. Irreducible complexity. But we can't go backwards, and we can't pretend planning is poison. We have to try, one misstep at a time, to design a future that actually works.