Temperature

Assuming my modeling of population and consumption is correct, then the famous 2° Celsius limit for global warming by century's end is twice what it should be. According to my first attempt to incorporate global warming into the model, if we are successful and the warming is already self-sustaining then we need to immediately start reducing our per-capita ecological footprint by at least 0.7% per year to avoid casualties between now and the year 2200.

A decline in total ecological resources due to degradation will have the same effect as consuming too much, eventually making it impossible for people to survive and our population will crash. Whatever causes it (global warming as an example) must be stopped before that critical threshold is reached, otherwise all we can do is delay the end date.

If, as I expect, humanity will soon be forced to consume less overall (through personally cutting back, losing population, or both), then our slowing rate of pollution will enable natural systems to process the lesser amounts resulting in the approximation of no net increase in the amount, and eventually a decline. In the case of greenhouse gases, I've assumed no decline in the next two centuries, which means that temperature (their effect on the environment) will not decrease either. As far as I can tell from my data, that effect has been masked by our overall consumption, so it hasn't yet resulted in a decrease in total resources; but with us now pushing against the envelope of those resources, there won't be enough left to both process our waste and provide for the survival of the species we directly depend on.

Perhaps by coincidence, my projected temperature will match with the historical trend in 2019, and others who are planning for future emissions seem to be targeting 2020 as their starting point. Also, I projected that direct emissions will decrease around the same time, except for short pulses corresponding to attempts to reach the resource limit after drops in population. For these reasons I chose 2019 as the starting time for a hypothetical decrease in total resources responding to global warming, and for attributing the difference in emissions to other factors that make it self-sustaining so that the temperature trend continues into the future.

The result, which is as close as I can currently come to a representation of future global warming, has consequences much worse than the case I first presented above, which is the best my model can achieve in terms of avoiding casualties with declining resources. Whereas my default case with no resource decline projects a world population of 5.8 billion people by 2200 (a "loss" of at least 1.5 billion), the global warming case projects that everyone will be dead by 2165. Adaptation in the form of limiting population and consumption growth adds only four years to that end date. For reference, in most scenarios I've looked at, the temperature above preindustrial times when the population crashes is about 2.5° C (it is currently 0.7° C, and would be 1.7° in 2100).