Will we crash, collapse, or shift? The answer is: I don’t know, and despite what some people say, neither does anyone else.
First a quickie on definitions. A crash and a collapse are very similar, and sometimes the words are used interchangeably. Which has been the cause of no few arguments in my experience. The core difference is the velocity of the change in civilization. Either way it is an unsustainable culture becoming a sustainable one due to an end of their ability to continue whatever unsustainable policy drove them. A crash is a relatively sudden change characterised by general famine, death, and possibly gruesome cannibalism. A collapse would be a more gradual deflation characterised by economic depression, an increase in the instance of famine, and possibly polite cannibalism. The commonalities are many. Both are undesired by the majority, and unexpected. There is no conscious control of either at any level, and the result of both is a culture that is devoid of most of the luxuries many of us have come to enjoy. But both ways the new culture is sustainable, not through any particular desire on the part of the people, but through a lack of alternatives.
A shift is very different. A shift is a conscious change from our unsustainable methodologies to a fully sustainable culture. The advantages of this are many. First and foremost, famine, economic depression, and even cannibalism become very unlikely occurances, unlike in a crash or a collapse. Another advantage, is we might be able to retain our luxuries. Probably not all of them, but with effort and genius most of our luxuries could be made in a sustainable fashion. The difficulty is found in the fact doing this would require the conscious and active will of the majority of the people on this planet. And we are somewhat lacking in heroic leadership at the moment.
Very few of the people who have studied the problem to any extent disagree that we are reaching the limit of our civilization. Our practices are unsustainable, and we are running out of necessary resources. If nothing else, this would mean a complete collapse of our economy. Such a collapse would make the Great Depression look like a holiday. If such a collapse was extreme enough, it would be a crash. Obviously this is not preferable and the result of a very short-sighted economic policy. That we still do this, when we know better, is criminally negligent at best, and genuine evil at worse.
The main disagreement between people is two-fold. First is the question of whether it is still possible to shift to a sustainable economy. The answer to this is usually either no, or people won’t do it even if it is possible, or the respondent’s unfailing humanism. The second major disagreement is whether we would collapse or crash, and there really is no general consensus on that question.
The main question is one of scale. We have historical records of many civilizations ending. Typically, the larger ones collapse, while the small ones crash. But, there has never been a civilization as large as ours. And those small civilizations where usually on islands, isolated and alone. Which would make it analogous to a planet-sized civilization without extra-terrestrial colonies, and hence, would argue for a crash. But, large civilizations were usually near enough to the whole world, especially for their time. And they collapsed. So are we a big civilization with a small outside or an island civilization? Do we collapse or crash?
My personal opinion is we should shift and leave the question unanswered. I am not sure a shift is possible at this point. But I have studied enough history to not write us off without a fight. The scale of the problem is almost without par, and the time we have is so short future archaeologists will have trouble differentiating then and now. To top it off, most people choose to bury their heads in the sand. And our global leadership is impotent, while most of the counter-culture leaders pushing for sustainability almost seem schizophrenic sometimes. But, people have the most annoying habit of surprising you when you least expect it.