The only place where births per woman are not close to 2 is sub-saharan Africa. Thus, the only place where family planning could reduce emissions is sub-saharan Africa, which is currently a tiny fraction of emissions.

This is not literally true: family planning can reduce emissions in the developed world if the desired births per woman is even lower than the actual births per woman. But I don't dispute the substance of the argument: it seems relatively difficult to claim that there's a big unmet need for contraceptives elsewhere, and that should determine what estimates we use for emissions.

Another point - more humans means more people to find solutions. So we have more people polluting the planet, but also more people working on clean energy solutions that will get us off fossil fuels.

As you might have seen, Project Drawdown is not my primary source. I came to my conclusions from various sources, which mostly agree on the general idea: Reducing population size and/or growth is a very effective means for positive change in several other cause areas. This does not rely on one single source.

Regarding the cost for providing contraceptives, the costs of less than 10 USD p.a. per user are well established. See, for example, this publication by the UN Population Fund (UNFPA):

Average direct costs to provide one year of method use are highest for hormonal methods—implants ($7.75), injectables ($8.61) and pills ($7.26)—with the commodities themselves accounting for most of the cost (Table 3, page 12). Permanent male and female sterilization and the IUD have the lowest annual costs when total method costs are divided by the average number of years users are covered by these methods. Annual average direct costs for male condoms fall between these method groups, at $4.17 per year.

As BenMillwood already mentioned, emissions reduction can be achieved almost anywhere, because in most countries actual fertility is higher than desired fertility. This gap varies from country to country but exists almost anywhere. At a current global birth rate of more than 130 million births annually, out of which more than 40% are unintended, I see big potential.

Which analysis of the beneficial effects on other cause areas do you disagree with, and why? I'd be happy to provide more sources and/or explanations, but for that I'd need to know which ones exactly you found to be weak.

I'd also like to point out that per-capita CO2 emissions in many countries will be rising in the next few decades and that, according to at least one peer-reviewed paper I cited, most of our efficiency gains that would reduce emissions were undone by population growth.

Fair points that I ignored the benefits of larger populations - you are completely right. I didn't do this, though, for the sake of brevity and because that is not something people need to be convinced of, generally.

If you claim, however, that there are large benefits to larger populations, then why bother with access to contraceptives in the first place - if people feel blessed with more children? Also, does that mean that societies should become arbitrarily large? It would almost follow from the points you raised.

Also, if you think that generally the benefits of children outweigh their costs, it should be common policy to have as many as parents want. This, however, cannot work on a finite planet with finite resources if parents would want, for example, to have at least 4 kids.

My personal view on this is that, as long as human population is below maximum carrying capacity (whatever that capacity may be - there are big arguments about it as you're probably aware), an additional human probably has a "net-positive" effect on total happiness/suffering. Once, however, the total population surpasses a certain point (which may be way above long-term carrying capacity - because initially, negative effects will still be buffered by resource surplus). Once however you surpass that point, additional lives will have a net-negative effect on total happiness/suffering.

Take, for example, the following thought experiment. You have a population of 20 and a good which they need. The good has a recovery rate of 100 per year and a current total amount of 1000. Every individual in the population (of currently 20) consumes 5 units per year. They can survive also at 4 units a year; when they only get 3 units or less for each of them, they would suffer. You could add more consumers to this system for a long time because of the total stack of 1000, which will initially only be depleted slowly. At one point, consumption needs to drop to 4 units per individual p.a.. Individuals would prefer to consume 5 units but they cannot, and they do not suffer terribly from suffering 4 (but their utility is already less than at 5). If you now add more individuals to the system such that every individual can only consume 3 units, people will suffer one way or the other - through suboptimal resource access or armed conflict.

What I am trying to say is: Until a certain point, more individuals means more total happiness for all individuals. This, however, likely drops at one point until more individuals mean less total happiness and more total suffering.

Leaving the thought experiment aside, are humans currently having a net-positive impact on other lives? Worldwide average meat consumption per capita is currently at 43 kg p.a., with up to 100 kg annually per capita in the US. That means that the average human causes intense suffering to dozens of sentient animals through his or her lifetime - lives completely lived in captivity in factory farms with incredibly stressful slaughter conditions. Is this a net-positive impact on total happiness/suffering? It seems to me a rather anthropocentric/speciesist view that does not take into account total suffering caused by millions of individuals.

Needing future generations for social security is, by the way, the equivalent of a pyramid scheme if following the current approach. Gains in productivity eliminate a need for increasing future generation sizes. Do check out per-capita GDP productivity growth - you will see that automation solves much of this problem.

Lastly, I want to point out that I would never support death of people currently alive - and I don't know why you would raise it. My post was clearly only about the gap of unmet contraceptive need. This is, obviously, ethically a completely different matter.

Edit: As I showed by citing several works related to the example of the Egyptian economy, a bigger population size does not actually translate into better division of labor, more scientists, and so on. It only does so if the state can grow its infrastructure and education opportunities alongside with the population. If the state can't, then you actually have a relatively lower proportion of highly trained/skilled workforce. This phenomenon is actually well studied in several developing countries which, currently, seek to slow down their population growth because the population grows much faster than the (relatively poor) states can ensure healthy economic development and opportunities for individuals.

Thanks for those links - pretty interesting!
I especially liked the "ROI analysis": "Through research into the most cost-effective development policies, the Copenhagen Consensus recommended expanding access to contraception universally as the third-best policy with a return to investment estimated at $120 per dollar spent [10]. [...] Family planning may have large benefits and ripple effects on various sectors, and is a large problem at scale."

It is indeed a very tricky question. Of course, there is a chance that each newly born child becomes a climate researcher, politician, social worker etc. - but what are the odds? And do they outweigh, as you mentioned, all the "bad" (for lack of a better work that encompasses suffering and future issues) points?

My personal view on this, as I mentioned in my reply to Larks is that, until a certain point (namely the point where there is neither conflict about scarce resources within human society nor intense suffering caused by human society to other sentient beings) each additional individual probably has a net-positive happiness/suffering balance sheet. Once the population has reached a certain size, however, this may tip. Total carbon emissions are a direct function of (number of emitters) * (emission levels). Total factory farmed animal suffering is a direct function of (number of consumers) * (amount of factory-farmed meat consumed). The average consumer nowadays consumes more than 40 kg of meat p.a. - that means that several sentient beings spent almost all their lives in intense suffering because of one average consumer. Is that a net-positive balance sheet?

Either way, my main point is about voluntary pregnancy avoidance and not about forced population reduction through whatever coercive means. If providing access to family planning counselling, women's education and empowerment means, and to contraceptives is so cheap - and at the same time links free choice with significant net-positive effects on several EA-aligned cause areas - what reasons would support not helping close that unmet need?

Reducing population size in richer countries has an even bigger net-positive effect on several issues, especially that of climate change. Per-capita emissions in developed countries are simply much bigger. Obviously, thus, I completely support population size and/or growth reduction in developed countries as well.

The difference between developed and developing countries, however, is the dimension of the unmet demand for contraception. Developed countries are usually able to provide those who want to prevent further pregnancy with affordable and effective means, whereas in developing countries there is a big unmet need. As stated in the opening post, more than 40% of pregnancies globally are unintended. Why should EA, given the significant positive effects on users themselves, not support closing an unmet demand?

Reducing mortality is obviously a positive outcome of these programs. The point of family planning programs, women's education, giving access to contraceptives etc. is increasing the quality of live and reducing suffering of individuals already in existence while, at the same time, eliminating negative effects of unintended pregnancies. Thus, reducing mortality is in line with the first goal.

Who decides what is the "correct" global population level? I see the "correct" level of population as a balance between life style ie consumption level and number of people. If everyone in the world adopted a western high consumption level then a low population  would be obvious, but if everyone lived sustainable simple life styles a higher level of global population would be  unproblematic. Proposing lower population levels could be viewed as culturally biased, ie rich westerners wishing to protect their high consumption life styles at the expense of other equally valid cultures. Dangerous ground to be avoided.

I think this raises some questions about the responsibility of developed countries to developing countries. A risk analysis of climate change impacts shows that it is plausible that developing countries suffer worse, even suffer their destruction, and that the global poor will suffer the most. 

On a per capita basis, carbon consumption of individual lifestyles could be globally leveled. The result though would be an opportunity for developing countries to seek more carbon release to the atmosphere as part of their economic growth. For example, they might 3x their per capita GHG production, while we have to produce 30x less than we do now. 

At the moment, populations in developing countries will suffer the burden of our historical carbon production. As that burden grows, their people will leave, if they can. From what I know of the popularity of refugees of various types in Europe, and in the US, developed countries will not welcome any sizable flow of migrants from any country. Sizable, meaning in the tens of millions.

This is the dangerous ground you mentioned. I think avoiding that dangerous ground requires that western countries curb their birth rates, drastically reduce their GHG production by a variety of means, and prepare to welcome a large influx of climate refugees. They also have to do what they can to proactively increase the consumption patterns of those in developing countries whose country is expected to survive climate changes.