In the early 1990s I read Beyond the Limits, a 20th anniversary reapprisal of the original The Limits to Growth. Then some time 3 to 5 years ago while I was visiting my parents I grabbed the book from the bookshelf in my old teenager's bedroom and looked at the scenarios they were considering. The last scenario which avoided a mid-21st-century global collapse required the introduction of sustainable policies by 2000. Introducing them later would not prevent the collapse itself, just change its character. Considering how well the 1970s model runs compared to the actual history up to 2005, things are not looking good.

In 2008 Graham Turner at the Commonwealth Scientific and Industrial Research Organisation (CSIRO) in Australia published a paper called "A Comparison of `The Limits to Growth` with Thirty Years of Reality". It examined the past thirty years of reality with the predictions made in 1972 and found that changes in industrial production, food production and pollution are all in line with the book's predictions of economic and societal collapse in the 21st century. In 2010, Peet, Nørgård, and Ragnarsdóttir called the book a "pioneering report", but said that, "unfortunately the report has been largely dismissed by critics as a doomsday prophecy that has not held up to scrutiny.

So, if you want to know

Is it fixable at all even with good will (that we don't see right now)?
How long it would take?
If nothing reasonable is going to be done where we are heading, for how long and with what consequences for states, world and  as well  for (most) individuals?And how it will end eventually?

I suggest that you get a copy of the 2004 book Limits to Growth: The 30-Year Update. Then you can diary it for us <grin>.

When you ask

What will happen with economy when at some point middle class become small and weak to hold this crazy concept of economy based on buying, borrowing, buying and borrowing?

I'm not so concerned with the middle class in its role as consumer engine of the economy. What I'm more concerned with is the industrial processes that are the necessary life support system of a human population numbering in the several billions. You need an educated middle class to keep that going! And by educated I don't mean economics and management "sciences" but natural science and engineering. See, for instance, the philosophy underlying The Lessons from the Veblen Farm. If that worldview is lost, and it is in real danger of being lost, the processes that keep our societies, countries, cities alive will begin to break down. In 50 to 100 years we may be like medieval people looking in wonder at decaying but still magnificent Roman structures with no clue how on Earth the Romans managed to build them. Or, even worse, early medieval people with an awareness of how they were built but also of their own inability to replicate the work. I see even peer-reviewed published scientific research degenerating into cargo cult science. Sort of like the sterile scholasticism of the middle ages compared with the work of the Hellenistic cultural elite.

When I think of best and worse scenarios I don't think so much about mortality rates in the great mid-century collapse (think 14th century Europe) but on the kind of culture that will emerge at the other end.

We are now in a position to use the last years or decades of the petroleum-fuelled material-growth industrial-production economy to lay the foundation for a sustainable material-stationary economy. But politically we in the West will do nothing in this direction. I wonder whether places like Japan will be able to push in a different direction, but it's possible that the entire OECD (the "rich" countries of the last 30 years) will pursue business as usual and wither with it. So, maybe if we want to imagine what the world might be like in 100 years we should imagine what the BRIC would be like in 100 years without the OECD's intellectual baggage weighing them down. China, Brazil, India, Russia, seem to pragmatically do what they must (as long as they can keep the wheels on their own carts), while the European policy elite are ideologues and do talking points.

In the short term, in Europe, I expect a 4-year cycle of total EPP dominance presiding over a Hooverian disaster. The second half of this decade would be one of real societal upheaval. After 2020, who knows. The one thing I'm confident about is that Jérôme will continue to help build wind farms through the political and socioeconomic turbulence.

Economics is politics by other means