Unfortunately, a transition to a more planned economy is going to be necessary, because individual actors working independently of the needs of others might be a surprisingly good way to allocate resources, but it's not smart enough to be done sustainably.

It doesn't need to be planned. The markets just need to be constrained and regulated. In some extents they can be expanded. E.g. you can force companies to buy and trade quotas for different types of externalities to cover undoing those externalities and let the markets sort out the most efficient way of addressing them.

There is complexity there (you need to ensure there aren't any easily exploitable loopholes), but markets have lots of uses.

> It's the most practical method we have right now for efficiently allocating those resources.

This is where true why is our way of life less sustainable today than it was 1000 years ago?

Nearly all first nations tribes lived in a way of live that was sustainable indefinitely. In 250 years of developing capitalism we have destroyed most of the biosphere, and trigger climate change that has the potential to undo civilization as we know it.

Capitalism and rapid hydrocarbon extraction has allowed the species to surpass the carrying capacity of the planet in away that cannot possibly be sustained.

Personally, I think this was always our destiny, but to try to delude yourself into believing that capitalism is making things better is a strange form of denial.

Because there are many, many more of us than there were 1000 years ago. Per capita, sustaining the lifestyle of a 21st century Westerner requires less land than that of an 11th century peasant.

It requires less land because of the heavy use of fertilizers and non-reproducing hybrid grains. It's literally and unquestionably and unsustainable process.

The CO2 emissions per person, which is a much better way to measure how much energy it takes to sustain a persons life style is unimaginably higher.