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Whenever I've heard Aubrey de Grey speak about defeating aging, he usually seems to downplay the potential impact on society and the planet that success in his project might have, and (to his credit) points out that it shouldn't be up to us to decide whether or not future generations should live a lot longer, and risk harming the planet by doing so - it should be up to them, and it is our moral responsibility to develop the tools to give them that choice. So it was with interest that I read this new study , sponsored by Aubrey's SENS research foundation, and the accompanying editorial by Aubrey , on statistical models of just what impact defeating aging in the coming century might have on human demographics and planetary sustainability. In , Aubrey says policymakers need to take into account the societal impact of defeating aging as projected in , but seems to downplay the magnitude of the impact, saying: [The projections from  show that] the actual, plausible trajectory of population growth following the arrival of effective rejuvenation biotechnologies only rather modestly exceeds the ‘‘base case’’ in which such technologies are never developed... Is "modestly exceeds" the base case scenario (no curing of aging) a fair way to characterize the projected impact of effective rejuvenation technologies described in ? I'm not so sure, and it doesn't seem like the authors of  are so sure either, at least by my reading. First, here are the two scenarios the authors of  using in their projects, based on differing mortality rates, one is the "base case" (people continue dying at a similar rate as today for the remainder of the century) and the other is the "Negligible Senescence" scenario (NegSens) in which scientists figure out how to stop aging in the next few years and it gets deployed over the next couple decades, at which point very few people will be dying: Based on this very low rate of people dying after the year 2040, the authors predict population growth based on three different fertility rates compared with the baseline scenario. In the baseline scenario, worldwide fertility rate drops from its current level of around 2.5 children per woman averaged over the entire world to 1.9 children per woman. In the (seemingly unrealistic) high fertility scenario, women start having more children than today once aging is defeated, with the fertility rate rising to 3.0, perhaps because they are living longer and are fecund for longer as well. In the mid-fertility scenario, the fertility rate is the same as the baseline scenario, i.e. 1.9 children per woman. This seems fairly reasonable it would seem, since childbearing / childrearing is an important part of many people's lives, giving them pleasure and their life meaning. In the low fertility scenario, fertility drops to 1.0 children per woman, "due to some combination of a reduced sense of self 'replacement' and 'old-age care' needs and of societal needs to limit fertility substantially to slow the rapid population growth of the underlying scenario." This last, low-fertility scenario may happen, but I'm skeptical societal attitudes about having kids will change that quickly, to the point that couples around the world on average only have a single child. But given these four scenarios (baseline and three NegSens fertility rates), here is the graph of population growth over time: The baseline agrees with most population projects demographers are currently making - namely that the global population will asymptote at around 10 billion around mid-century and then starts gradually declining. If women seriously curtail the number of kids they have, the low fertility NegSens scenario shows population growing only gradually to around 12 billion by the turn of the century - not too dramatic. But if women continue to have nearly two kids each, population will continue growing, to around 15 billion by the turn of the century. The high fertility NegSens scenario has population growing to a whopping 20 billion by the end of the century. In the remainder of the paper the authors pretty much ignore this high fertility scenario, as unrealistic and/or too depressing... One of the most interesting projections is the impact of the various scenarios on greenhouse gases. The authors point out that it is obviously quite sensitive to the mix of energy production methods (i.e. fossil fuels vs. renewables), but the authors project that neither the low nor medium fertility rates will substantially change carbon dioxide equivalents level in the atmosphere relative to the baseline scenario, with all three resulting in a pretty substantial increase in greenhouse gases over today's level of around 400 ppm to around 600 ppm by the turn of the century, or 800 ppm if we continue to use a lot of coal and other fossil fuels in our energy production mix. Those numbers are pretty depressing, given the temperature rise and climate effects the scientists are predicting unless we reverse the trend and keep greenhouse gases well below the current level of 400 ppm... In terms of worldwide hunger, the authors predict that with better food production / distribution methods, and a stable population, the baseline scenario will result in a dramatic reduction in hunger and starvation around the world by the turn of the century. But with a growing population as a result of defeating aging, we could see a world where hunger and starvation remain a problem of similar magnitude as today, as illustrated in the graphs below: Here is the most important paragraph from the author's conclusion: Finally, our results point to perhaps the greatest challenge facing a world of negligible senescence, those relating to the sustainability of our natural resources and biosphere. Given widespread concern that our economic way of life is already unsustainable, 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. So in a sense Aubrey is right - global resources would be strained by defeating aging, but given a reasonably projection of fertility changes (dropping to 1.9 kids per woman worldwide), things won't go completely off the rails, at least by the turn of the century. Of course history won't end at 2100 (hopefully!), and in this 1.9 fertility rate scenario, population will continue to climb steadily, while the planet and its resources won't be getting any bigger... Perhaps by that time Elon Musk will have succeeded and we'll be colonizing Mars, so will have a lot more room and resources for humanity to expand. But I'm not holding my breath on that one, given the challenges of making Mars habitable and getting people there en mass. We live in interesting & challenging times, and it seem like things are only going to get more interesting & challenging. My primary reason for pursuing health / life extension is so that I can be around to see how things turn out - it promises to be quite a show! --Dean ------  Technological Forecasting and Social Change, Volume 99, October 2015, Pages 77–91 doi:10.1016/j.techfore.2015.06.031 Opportunities and challenges of a world with negligible senescence Barry B. Hughesa, Randall Kuhnb, Eli S. Margolese-Malina, Dale S. Rothmana, José R. Solórzanoa Free full text: http://www.sciencedirect.com/science/article/pii/S0040162515001985 Abstract The development of anti-aging technologies could have dramatic implications for a world already challenged by population aging. We explore how the world might evolve given the development and deployment of technologies capable of nearly eliminating mortality and morbidity from most causes. We consider both the great benefits and some of the complex sociopolitical rebalancing resulting from such advances. We use the International Futures (IFs) long-term, multi-issue, global forecasting system in our analysis of the interactions among demographic changes, the related changes in health costs and government finances, shifts in labor force participation, resultant economic transformations, and the environmental sustainability of the dramatically-altered human demands that emerge. We find that the widespread deployment of anti-senescence technologies would cause populations to surge—making fertility rates an issue of tremendous social import—while a much larger, healthier, labor force would spur economic growth. But this is not a given; the cost of treating entire adult populations could prove unbearable to non-high-income economies without significant transfers within and across societies. In the absence of new transformative production technologies, life-pattern financing would require the virtual elimination of retirement and a major restructuring of government finances. Pressures on the environment would also greatly intensify. ---------  Rejuvenation Research. October 2015, Vol. 18, No. 5: 387-388 What Will a Post-Aging World Really Be Like? Finally, A Tool to Help Us Predict de Grey Aubrey D.N.J. Full text via sci-hub.io: http://online.liebertpub.com.sci-hub.io/doi/full/10.1089/rej.2015.1786 Excerpt: ... I am gratified to say that the findings reported in this article accord very strongly with my historical intuition. The conclusions are presented in a suitably cautious manner, incorporating stern warnings of the consequences if humanity fails to anticipate the impact that the arrival of these medicines will have on demands for food, sustainable energy, and, of course, the medicines themselves. However, that is indeed the purpose for which we sponsored this work—for two reasons. First, by setting out properly evidence-based projections through to the year 2100 of a few sample scenarios of how the various regions of the world will fare and what they will experience in a post-aging world, the paper lays to rest the far more pessimistic knee-jerk assumptions so vocally expressed by so many when the topic is discussed. The actual, plausible trajectory of population growth following the arrival of effective rejuvenation biotechnologies only rather modestly exceeds the ‘‘base case’’ in which such technologies are never developed, and it is vital that opinionformers and policy-makers should understand that fact if they are to make wise decisions concerning near-term investment in the long-term future.