I think a good measure of human civilization's size is world GDP. Carl Shulman has already linked to Hanson. If we look at Brad DeLong's trend of GDP produced by humanity, the future must be "new" in that this can't continue super-exponential growth another few centuries. It seems physically impossible for humans to double their economy say every month. What happens when this trend stops? I don't know, but maybe
A different question is whether you can take effective, tailored actions like MIRI attempts in response to one of these possibilities, without any causal model of how it would arise. (In other words, with global warming we can model the climate system at least somewhat.) I currently doubt it because it seems that with such limited knowledge, any actions are likely to be either totally ineffective, or effective against bad outcomes but also good outcomes--so we could renounce fast computers to defend against AI but that might starkly limit humanity's potential. We may be playing blackjack but don't yet know if the maximum hand is 21 or 2100.
What, in a broad sense, does the future look like? We don't know, and while many have historically made predictions, the track record for such predictions is less than impressive. I have noted that there appear to be two main types of view about the future-- the "new future" and the "business-as-usual future." In order to simplify this discussion, let's restrict it only to the coming century-- the period between 2013 and 2113.
The "new future" is, generally speaking, the idea that the coming century is going to be very different from the present; the "business-as-usual future" is, generally speaking, the idea that the coming century is going to be very similar to the present.
Here are some characteristics of the new future:
Here are some characteristics of the business-as-usual future:
Reference class forecasting seems to indicate that the business-as-usual future is quite likely. But as we know, this is far from a textbook case of reference class forecasting, and applying such techniques may not be helpful. What, then, is a good method of establishing what you think the future will look like?