A new version of my Timelines model introduces a simulated history, Timeline 2, that is a better match to real history than the previous one (Timeline 1) and includes more variables. The following discussion is based on that timeline with reference to events in our own past. References to years after 2013 are entirely based on projections for Timeline 2.
In the second decade of the twentieth century, science and technology was undergoing revolutionary innovation, especially in the areas of physics, medicine, and transportation. They both aided, and were aided by, the conversion of energy, material, and other life into forms that humans could not directly consume in the wild ("waste"), whose yearly impact on natural ecosystems for the first time in history exceeded what the entire population needed for basic survival.
Three decades and two world wars later, that innovation along with global awareness and social innovation was coming to terms with the consequences of that waste. Among the benefits was an increase in life expectancy (when the death toll of war was excluded) and increased potential to customize people's individual environments, reflected in life satisfaction (happiness). Costs included the potential for a few people to inflict harm and death on a large fraction of the world's population, intentionally or by accident.
By the 1950s, waste was more than double the amount humanity consumed to survive, and that ratio grew faster than it would any other time before 2020. By itself, our timeline's waste was one-eighth of all life-related resources on our timeline, while Timeline 2's waste was one-seventh of its resources. This included both reusable resources and the creatures that produced them; but the fractions of just reusable resources were three timesas much.
The limit of reusable resources was passed on both timelines in the early 1970s, with each converting more than three times as many resources into waste as were consumed for basic survival. By then, it was glaringly obvious that the environmental was deteriorating on a global scale, especially in response to pollution. At the same time, supplies of fossil fuels that had enabled much of the previous years' growth were becoming harder to find and economically extract.
Scientific and technological research focused in response on increasing energy and material efficiency to reduce the speed of resource use and the harmful and costly impacts of continuing the lifestyle that waste had enabled. It also also turned toward repair of the damage already done and identifying how humanity could survive if the situation got worse. Biotechnology explored the alteration of biological systems, including food sources and ultimately humans, so that a variety of different resources could be used and harsher environmental conditions could be tolerated. Space exploration, initiated in the 1950s in tandem with mini-wars and rivalries that barely avoided devastating scenarios enabled by the last world war, served as a test bed for technologies that might help people escape Earth and survive in the most inhospitable of environments.
These developments were accompanied by a reduction and leveling off of the waste-to-needs ratio, which was a result of growth in population (and its associated needs-consumption) exceeding the growth of waste production. That waste, by 1998 in Timeline 2 and 2003 in our timeline, itself took up an amount of resources equal to the reusable resources (technically, an ecological footprint of one Earth per year), with needs taking up one-third as much.
Until 2005 in both timelines, life expectancy could be expected to increase along with waste-driven economic activity. After that year, though, that advantage became a statistical disadvantage and then a liability. More affluent people were able to live longer, so the fraction of children (people younger than 20) fell for what was already a small part of the population to a level where life expectancy became effectively zero for the richest in 2016. Life expectancy continued to increase for the younger and less affluent, driving the population average upward as more people gained access to the technology embedded in the still-growing waste.
By 2020, waste will have rendered dead or unusable half of the entire world's life-based resources. This would coincide with a peak in total human population, two-thirds of them adults, consuming enough in needs and wants to leave only one-third of the world's original resources intact for planetary life and life support.
The urge to grow older might be behind what is likely to come next, if a series of possible natural catastrophes, perhaps related to climate change, doesn't reduce the remaining resources on their own. Continuing growth in waste that enables survivors to grow older will by 2022 cause the growth in life expectancy to stop for the average person in the population and decrease after that. This might be perceived as increasing protection of the younger people more likely to have children, but with more people dying than being born this will be a fleeting advantage at best.
The world economy, measured in Gross World Product and wealth, based on transactions of products and services mostly consisting of waste, will continue to grow until 2025 and then fall as the loss of people able to make transactions offsets the growth in waste.
Average life expectancy will be zero in 2031, followed by population (and of course, the economy) in 2038. The waste created by humanity will persist longer, such as greenhouse gases that could still be warming the atmosphere for thousands of years. After we have briefly benefitted from it, it and the destruction it has caused will be our most consequential legacy.