http://www.washingtonpost.com/blogs/wonkblog/wp/2013/10/29/j...
I doubt any of these models will be accurate. But do they need to be? Either our technology will make our current lifestyles sustainable, or reality will catch up with us and cause much distress.
See also The Rational Optimist by Ridley, The Improving State of the World by Goklany, etc.
This is the road we are on: hideous mass death or utopia. I don't see a third possible outcome. Exponential stuff is like that-- the only potential outcomes are extreme.
Makes me wonder if the ancient religious visions -- e.g. Revelations -- about a 'heaven or hell' outcome aren't prescient bits of intuition about the fundamentally binary nature of human destiny. One way of thinking of it is that we're a cosmic civilization in its early startup phase... meaning that success or failure are the only two possible outcomes.
What a fantastic question! You're thinking in the right direction.
The explanation involves systems theory, so I'll let an expert explain. https://youtu.be/HMmChiLZZHg?t=420 1h30m, but it's the best explanation of Limits to Growth out there.
This is what complex systems do. Simple linear causal reasoning just breaks down... there are too many feedback loops, chaotic functions, etc. Things will look completely normal and then wham, the system will suddenly and without apparent warning undergo a radical shift.
Look at how economic bubbles pop. You'll have a roaring, humming economy collapse within hours or days and nobody knows why. The postmortem generally takes years. Sometimes the reasons seem 'obvious' but that is only in hindsight. Nobody ever succeeds in calling the top of a bubble -- despite the huge financial reward of doing so -- except by sheer luck.
LTG was an attempt to apply complex systems modeling at the global scale to answer questions about the long term viability of our current civilization. So far it seems to be tracking reality in some ways, but as you correctly state we do not know whether this is spurious correlation or actual evidence for the validity of the model. We also know -- see the work of folks like Ilya Prigogine -- that it is actually impossible to predict the future of systems like this with certainty. There are strict limits on prediction in complex systems.
So we don't know. LTG is scary, but for all we know it won't come to pass.
But we'll know soon. We get to find out in the next 25 years if all the work we've done to build a better future over the past 500 years is a total mirage and all our children are all doomed to starvation, warfare, and misery. Fun times.
The model then predicts a sudden shift in 2025 without any inherent explanation. There's a vaguely-defined downward-sloping "resources" line on the graph that seems to drive the sudden shift, but there's no actual data given for the 1975-2000 period to know if actual "resources" are tracking the model. I'd guess not --- as much as the Bakken shale oil formation may have some serious environmental impacts, it (and many other discoveries) have dramatically increased energy resources. Food production doesn't show any signs of immediate collapse. Renewable energy is still expensive, but it's getting better faster than many expected. Etc.
So, 25 years of steadily increasing population does not validate this model in any meaningful way. The model depends on a sudden shift in ~2025 that no empirical evidence supports. It might still happen -- I can't rule it out -- but the data given hardly confirms this model.