Given that the world has been exponentially using more resources than are being replaced (either through discovery or reprocessing), there does not appear to be any way to avoid the world’s population eventually decreasing. My population-consumption model does however suggest two alternatives that can postpone the fall (but only as long as they are applied): Increase total resources by at least 3 percent per year; or decrease per capita consumption by at least 1.5 percent per year.
By decreasing per capita consumption (how many resources are consumed per person per year), the drain on non-renewable resources is reduced. If the resources are the ecological resources included in the global ecological footprint, this can only continue until people begin starving to death (we are currently consuming 2.5 global hectares per person; the limit may be around .05 hectares, reached in 2119 if we start now).
If we increase total resources, more people can each consume more. In the case of ecological resources, we must increase renewable resources at the same rate; if we can’t, then the required annual resource increase is closer to four percent. For ecological and energy resources, this means that if we started immediately, we would need to add two units of resources for every one unit we consume (we are currently adding 1/24 and 3/4, respectively). As I’ve pointed out numerous times before, we would still be limited by how fast we could reach the new resources; beyond the inevitable maximum speed, consumption and population would both decrease rapidly.