That's a huge "what if", on top of what's already an impossible-to-predict situation. But if we're going to entertain this, we should also factor in the other circumstances that are likely to come with this scenario:
I spent a chunk of my life adjacent to bio/med research and my conclusion is radical life extension by purely biological means will probably remain unfeasible. Genetically, we're millions of years worth of horribly interdependent spaghetti code, there is no fixing this mess. So - barring the option to upload yourself to silicon - death won't be obsolete by 2065.
However we might see some very, very moderate increases in life expectancy across the board, even in comparatively poor nations, as long as they're not living in abject poverty. This would be cause for concern, but data from industrialized nations suggest a major regression in births once a population becomes (somewhat) wealthy and healthy.
The desire to procreate boundlessly may very well be a deep-seated instinct triggered by living in precarious environments. If dying slows down, it's because of improved living standards and medical care, the same things that stop over-procreation.
It seems to me that in order to control Earth's population, we need to address poverty, which incidentally would solve a huge slew of other humanitarian and ecological problems.
First, I don't think you are adequately compensating for the availability of new technologies, such as medical molecular nanotechnology, which we will certainly have by 2065. The entire approach to medicine that we use now is likely to be obsoleted in that time frame, leading to the eradication of most terminal diseases.
Second, one doesn't have to eliminate biological death entirely to muck up those forecasts. We know from super-centenarians that those who are lucky enough to not suffer any life threatening conditions nevertheless kick the bucket around age 120. Even if that's not fixed by 2065, it's almost double the average life expectancy and that is not factored at all into the OP's calculations.
Third, birthrates are currently constrained by menopause in women. Most women don't have more than a few children in the developed world because they are biologically incapable of having more. And although men have the capability to have "2nd families" (with another woman later in life after their previous children are grown), women do not. Defeating/controlling menopause is therefore more likely to result in either larger families, women choosing to have a second family at a later stage in life, or women who would have otherwise missed their chance having a family at all. Again, fertility advances are not factored into the OP's calculations.
Thus although I could argue that biological immortality is not "unfeasible", I don't need to. The OP has failed to factor in reasons why the death rate will go down and the birth rate will go up, making his charts too conservative.
To me, it also means that the "upload to silicon" stage is unlikely, because it probably requires understanding and reimplementing (possibly bug-for-bug, in some places) the original, for, uh, carbon compatibility. (And if we really understood it that well, we'd probably just fix the original...)
Medical care is unaffordable / unsustainable in the high HDI countries and doesn't exist in the low HDI countries.
Would have been interesting to look at the impact on the high HDI countries of mass invasion and demographic replacement. Many of those countries won't be in the "very high" category much longer. That will have the obvious impact on birth rates etc. Ditto long term trends in income inequality, in that population stats meant something when populations were more equal, but the average of oil and water isn't a salad dressing.
> Medical care is unaffordable / unsustainable in the high HDI countries
Maybe. Or maybe we're so wealthy and have so few kids that the health care industry is draining off the excess?
In either case, I think it's hard to make such generalizations about a group that includes both the US and countries that have single payer health care.
"A common objection against starting a large-scale biomedical war on aging is the fear of catastrophic population consequences (overpopulation). This fear is only exacerbated by the fact that no detailed demographic projections for radical life extension scenario have been conducted so far. This study explores different demographic scenarios and population projections, in order to clarify what could be the demographic consequences of a successful biomedical war on aging. A general conclusion of this study is that population changes are surprisingly slow in their response to a dramatic life extension. For example, we applied the cohort-component method of population projections to 2005 Swedish population for several scenarios of life extension and a fertility schedule observed in 2005. Even for very long 100-year projection horizon, with the most radical life extension scenario (assuming no aging at all after age 60), the total population increases by 22% only (from 9.1 to 11.0 million). Moreover, if some members of society reject to use new anti-aging technologies for some religious or any other reasons (inconvenience, non-compliance, fear of side effects, costs, etc.), then the total population size may even decrease over time. Thus, even in the case of the most radical life extension scenario, population growth could be relatively slow and may not necessarily lead to overpopulation. Therefore, the real concerns should be placed not on the threat of catastrophic population consequences (overpopulation), but rather on such potential obstacles to a success of biomedical war on aging, as scientific, organizational, and financial limitations."
That study is flawed. It's "optimistic" scenario still assumes menopause and therefore a fixed number of children per woman in the population. Yet a level of medical technology that can eliminate aging entirely would also be able to reset the biological clock (or create artificial wombs, etc.).
Or at least, many fewer people. If we get to a point where we're extending the average lifespan by a year every 7 or 8 years, up to an average ceiling of around 100, that has big implications. Demographic trends can probably predict birth rates decently, but probably not the overall population 50 years into the future.
I spent a chunk of my life adjacent to bio/med research and my conclusion is radical life extension by purely biological means will probably remain unfeasible. Genetically, we're millions of years worth of horribly interdependent spaghetti code, there is no fixing this mess. So - barring the option to upload yourself to silicon - death won't be obsolete by 2065.
However we might see some very, very moderate increases in life expectancy across the board, even in comparatively poor nations, as long as they're not living in abject poverty. This would be cause for concern, but data from industrialized nations suggest a major regression in births once a population becomes (somewhat) wealthy and healthy.
The desire to procreate boundlessly may very well be a deep-seated instinct triggered by living in precarious environments. If dying slows down, it's because of improved living standards and medical care, the same things that stop over-procreation.
It seems to me that in order to control Earth's population, we need to address poverty, which incidentally would solve a huge slew of other humanitarian and ecological problems.