I hope that the next 30 years will be much better than my attempts at projecting the future have indicated. They will almost certainly be different – and interesting. At the very least, I want to be able to look back (assuming I live that long) without regretting the way I spent that time.
My latest projections are now being tested by experience. Interestingly, the latest element of my analysis is the subject of worldwide attention now: the potential progress and impacts of global warming. I have taken time off from writing and modeling to follow the COP-21 negotiations in Paris, and to acquire and process the latest news that pertains to my research. Coincidentally I am facing some personal and professional deadlines that require planning inputs just like the projections I have been working on. As a result, I've decided to use the projections I currently have, for both planning and discussion, with the goal of incorporating the results of those uses into a future update of the model that produced them.
I've created a part of my research Web site that is dedicated to this process, and chosen to focus on two sets of projections which I have discussed previously. The "default" case is the second of two stories that my research has revealed, where humanity begins consuming resources needed to maintain our survival. The "warming case" involves the influence of self-sustaining global warming in combination with our behavior in the default case, which drives our species to extinction by 2165.
Embedded in both of these reference cases is a fundamental assumption about values: that happiness, enabled by using ecological resources (footprint) to customize individual environments, is much more important than people's lives and the lives of the other species whose demise is causing people to die. As total resources decline due to global warming, some surviving people will be still able to consume much more than others, but humanity as a whole won't be able to recover its numbers.
Key to validating, understanding, and possibly mitigating these catastrophic trends is the identification of the critical "producer" species assumed to enable the survival of the "supporter" species that we directly depend upon for our survival. While I don't know what they are, I do have some guesses, chief among them the creatures that enable plants to survive, such as birds with their dispersal of seeds and nutrients, and the fish which keep many of them alive. I have recently been studying the condition of soil, which I expect will reflect our impact on producer species. The fact that one-third of remaining soil is degraded, plus the recently revealed fact that Earth now has two-thirds of the arable land that existed 40 years ago, means that we have less than one-quarter of the healthy soil we had at that time. Interestingly, my calculations show that we now have about one-third of the extra resources (resources not directly consumed by us and supporter species) that we had in 1975.
The first significant decline in our own population is projected to occur in the next few months, with around 200 million deaths due to lack of resources, most likely food. This will be the clearest possible signal that we have begun killing off the last producers alive on Earth; though we may not initially recognize it as such because we will directly be seeing its impact on the supporter species. By 2017 we will have recovered, perhaps due to artificial replacement of what the producers were providing along with some recovery of the producers. We will see a smaller death rate the following year as we attempt to consume more, and probably try a similar fix in 2019. By 2021 the two cases diverge: in the warming case, our recovery will couple with the effects of climate change and we will see the greatest, fastest population drop in history, with more than a half-billion people dead; and, after another recovery, a second drop will occur with almost the same magnitude. The default case, meanwhile, has its greatest population drop in 2023, with more than 300 million people dead, though there will be other, smaller "drops" in the future.
One thing (among many) that I don't account for is the impact of having births make up for drops in population, the most obvious part being the growing fraction of young children over time. That will foreseeably reduce the ability of humanity to maintain its growth in consumption, unless machines grow sophisticated enough to do so without human intervention. A similar argument applies to producer and supporter species, which must grow back, at least partially, and may not grow to be mature enough to provide the products and services expected.
The smartest thing we could do following a population drop is to resist growing the population back and to try lowering per-capita consumption to a sustainable level (at least long enough for other species to recover their numbers and maturity) and then maintain it at that level. If we don't do that on purpose, then perhaps the changing demographics will have the same effect.