The second part of overshoot, environmental degradation, greatest impact will come from climate change. That is not to say that standard environmental degradation; destruction of farmland, atmospheric pollution, etc, will not be a major problem but compared to climate change these are simple, predictable and linear events, climate change is unpredictable, complex and non-linear. Heres an example of a climates systematic complexity, XKCD cassini. Notice that he said that the level of complexity exhibited by that single valley of Chad is found everywhere.
The practical side of this is simple; I can’t use the regional/local effects of climate change as an assumption, with any accuracy, because the effects are completely unknown, and unknowable, to me at this scale. In the various models I’ve seen, the only consistency I’ve seen is that the south of australia gets wetter while the north gets drier, only one model showed the changing rain patterns (more sporadic and evaporates faster). Some things can be guessed, such as more extreme weather events, more variability and such, but specifics can’t be guessed easily on anything below a continental scale.
This means I haven’t used climate change as an explicit assumption, only a an implicit. So, I assume at the end of the peak oil transition that our climate will share similarities with its current state, being only more extreme and with shifted bioregions. I highly doubt this is what we will face, but it’s the best guess I have. Without more accurate and exact climate models the best way to deal with possible major unforseen changes is through willingness and preparation to adapt.