Paradigms (from wikipedia) describe distinct concepts or though patterns in any scientific discipline or other epistemological (and yes, I did look that word up) context. Overshoot demands that we change, at the very least, our worldview paradigm to account for the changes that will sweep throughout our world. While peak oil means oil production will decline, the changes that that shift brings will not be a reversal of those born of oil productions rise, but it will share elements of a reverse. Climate change is effectively, the other main component of overshoot, a global experiment to find out what reverting our planets biosphere back into standard hothouse conditions looks like from the inside. As we accept the decline, we will have to change ourselves in response.
Economic assumptions will change drastically as both the net and absolute energy available to humanity declines. Since peak oil will hit transport first (60% of oil is used for transport) and most renewables supply electricity not fuel, we can start there. The gradual erosion of global trade will reduce the importance of imports/exports over a national, then regional, scale and act as a pseudo tariff which will both allow actual tariffs or trade barriers (due to the reduced influence of traders) to be implemented and rise over time until new sustainable (sailing ships) transport has been introduced. Localization, caused by this, of the economy will also revitalise the household economy, which functions differently to the market economy, such as being more resilient but also being less efficient, necessitating a new operative procedure. As energy becomes more expensive the equations that govern current industry practice change e.g. Hand labour for a smaller (high quality) output becomes more economical than mass production. These are only some of the changes that will occur.
Ideology and culture will also be forced to fragment and relocalise. As the infrastructure necessary to maintain the mass culture (a national culture with many regional cultures is certainly possible) degrades, it will dissolve into an environment filled with now resurgent local/regional cultures that will now have greater staying power. This will fragment nation-states into smaller, more homogenous units, effectively smaller national units, although many states could still survive where no strong nation exists today, other large identity groups will also fragment. Here I expect the Australia to remain; the man from snowy river type of nation building is possible in a post-overshoot world, but the states to become more autonomous and powerful than they are now. Ideologies will also change, even “think globally, act locally” will out of necessity change to “think locally, act locally” as the world gets big again. As communication systems decline we will know far less of what’s going on in the world and as energy availability declines we will less and less be able to affect other parts of the world (acid rain, global warming etc) while those parts can’t affect us as easily. While ideologies can function within a larger framework, like medieval Christianity, these frameworks can only form above a grassroots level after a decline and even then they take a long time to form, paganism was rampant in large parts of Europe (Vikings, Lithuania, Russia etc) well into the 12-14th centuries. Focusing on global problems at the expense of local ones is slowly, but at an accelerating pace, becoming non-viable.
These are only some of the realms that the paradigm shift will affect. The effects will be spread over a long-time but we can begin preparing now and start shifting our worldviews to match what our world is becoming.