A Demographic Model of a World with Negligible Senescence
Few serious efforts have been made to generate robust demographic models of a near future in which radical life extension is achieved through rejuvenation therapies such as those of the SENS research programs. There is a paper from 2010 and little prior to that. Here a more recent model adds consideration of economic factors; the purpose isn't to predict what will happen, but to try to explore the likely nature of relationships between therapies to treat aging and extend healthy life spans, demography, and economic line items such as energy use and retirement.
Since the model used only explicitly factors in progress in technology via increased productive life span and GDP, I suspect the authors overstate concerns regarding energy and food. Even so, within their model the situation is hardly the Malthusian disaster predicated by people who subscribe to the overpopulation myth. The same model run in the 1930s, well before the green revolution in agricultural output, would probably have indicated far worse issues for food supplies, and also for the environment given the state of power generation technologies back then. Technology is not static, and efforts to improve it in specific ways are carried out in reaction to perceived shortcomings and expenses.
There is near certainty that the world will experience rapid population aging throughout this century, thanks primarily to widespread and substantial reductions in fertility and, secondarily, to ongoing extensions of life expectancy. Even as debate persists on biological limits to life, a growing body of demographic evidence suggests that improvements in human longevity are not diminishing, and may even be accelerating at older ages. At the same time, new breakthroughs in regenerative medicine and anti-aging therapies point to the possibility of improvements in longevity that are dramatic rather than incremental, and that reduce morbidity along with mortality. Yet, forecasts produced by governmental and intergovernmental organizations continue to assume a fairly narrow range of upside longevity variation, amounting to at most 10 years of added life expectancy. In this study, we take the opposite approach, exploring a future of very rapidly expanding life expectancy coupled with very low senescence. Using International Futures, a large-scale, long-term, integrated forecasting system, we explore the demographic, socioeconomic and ecological consequences of, and necessary adaptations to, such a world.The purpose of this paper, then, is to consider the issues raised by a future of very rapidly expanding life expectancy coupled with very low senescence. More specifically, we want to look at how the world might evolve were there to be, over a 20-year period beginning as early as 2020, a rapid development and deployment of technologies that nearly eliminated mortality and morbidity from disease as well as eliminating infecundity. We label this world that of a Negligible Senescence scenario. We juxtapose this world with a Base Case scenario of more slowly progressing extension of life expectancy, accompanied by delayed but not ultimately reduced senescence (a more common forecast than that of negligible senescence). Our goal is not to model a likely future world, but rather to frame our understanding of the potential consequences of negligible senescence by evaluating the effects of a rapid and universal transition to such a regime.
We find that a world of negligible senescence would pose a number of immense challenges that go well beyond increased population size. The most obvious and immediate challenge lies with disseminating and paying for the life-saving intervention set itself. We estimate that rollout of such an intervention on a widespread basis would be infeasible even in the wealthiest countries if the initial price were set at $10,000 per year of healthy life added. At the price of $5000 per added healthy-life-year that we assumed through much of this paper, the initial financial burdens would be manageable for wealthy countries and would, over time, yield considerable reductions in disease-related expenditures that would more than offset the cost of the intervention. Yet poor and also middle-income countries would struggle to finance such an intervention even if, as we assumed, up to 95% of the costs in the poorest countries were defrayed through price reductions of the sort that have recently been observed for high-impact antiretroviral treatments.
With these caveats in mind, a world of negligible senescence would likely yield a still growing population of 14.8 billion by the year 2100, a considerable increase over the 7 billion today or the 10.1 billion forecast in our Base Case in 2100. Uncertainty in fertility, arising from the potential pronatalist impact of increased fecund spans and, on the other hand, the public interest in reducing fertility to check population growth, could yield a population with as many as 20 billion or as few as 11.6 billion.
A revolutionary jump in human longevity would require a comparable revolution in the meaning and timing of retirement. We explore scenarios that would see the average age of retirement rising to 114 by 2100 if fertility remained moderate. Even these relatively aggressive increases in retirement age necessitated a rise in savings from 22% today to 29% and doubling public pensions as a share of GDP, from 6% to something more like 14%. These increases would seem to be at the absolute edge of feasibility, and thus our retirement age scenarios should probably constitute something of a lower bound. On a positive note, individuals would still be able to enjoy decades of post-retirement life if they so chose, or embark on new patterns of employment, education, and leisure that are less defined by imminent mortality than the current pattern.
The potential addition of billions of people would concern many, especially given that this population (in the absence of negative feedbacks from environmental constraints) would see a GDP per capita 30% above the already substantial economic growth built into our Base Case. Energy demand levels, even with quite optimistic assumptions about efficiency gains and renewable contributions, would drive atmospheric CO2 levels above 600 ppm and, if coal were more heavily drawn upon without carbon sequestration, to 800 ppm or above. In the absence of food production technologies that are currently not on the forecast horizon, it might become nearly impossible to reduce the portion of the world's population that is undernourished.