Population
All environmental and sustainability issues are impacted by population. Even the most wasteful and polluting industrial processes would have minimal environmental impact if the population were small enough. Unfortunately this sensitive topic does not get the attention it needs.
Population is Self-Correcting
All evidence shows that education, especially women's education, low infant mortality, and access to birth control naturally result in a declining population. It is a self-correcting problem.
We just need to avoid creating economic systems that rely on an increasing population to fund things like retirement pensions and growth for growth sake economics. And ignore people with outsized platforms who promote these ideas.
Population Control is Not Genocide
When you say "overpopulation", many people only hear "Thanos was right". Or at least they did in 2018. But this is a problem that can easily solve itself without resorting to genocide or authoritarian limits on births. Yes, overpopulation has the taint of its past support by eugenicists, the CCP, and other racists. But is population control racist just because some racists have taken up the cause to promote anti-immigration policies? Is it racist to make birth control and family planning education available to everyone? You can oppose racist population control policies without abandoning the goal of reducing the global birth rate through voluntary action.
The solution is likely to support programs that provide easy global access to family planning without ever talking about overpopulation in order to avoid being called a racist genocidal white savior. Focus on the issue of women's empowerment and equality instead. Hopefully the problem will sort itself out and we won't have to address it directly because people are a bit touchy about the subject.
Sure, There is Plenty of Food...
Yes, we we grow enough food right now to feed a population nearly 20% larger than our current one. Good for us!
However, food is not the only resource. There are a million things that must be mined, grown, caught, or otherwise removed from the environment to produce all of the things that go into a modern capitalist society. Only so many of these things are renewable, and only so many of the renewables are being used sustainably. We may or may not be able to use technology to find alternatives. We're going to run out of many things faster and have less time to find alternatives the higher the population.
Then there is the value of nature and natural spaces, and the existence of other species besides us and our food. Even if vertical farming allows us to stop turning more and more wild areas into farms, without a stable population the land will be used for housing, transportation, resource mining, or other human purposes, further diminishing the space available for nature.
Eventually some resource is going to run out, or something is going to extinct, that has a real impact on our quality of life or our survival. Or a lot of little things will add up to a big impact. In any case, population reduction will delay all of the non-renewable issues and resolve many renewable ones by making them sustainable. It is a single solution that impacts every environmental problem. To ignore it as a solution because it smells a little like racists despite having no inherent racism is self-defeating and absurd.
Quality of Life Issues
The quality of life issues surrounding population are rarely part of the discussion. There is only so much land available to live on if we still want to have a nature. Everyone wants to obtain the same standard of living now enjoyed by the richest 1%. This cannot be done sustainably with a growing population, or even the current one. And humans will stubbornly resist any attempts to enforce economic changes that reduce their quality of life.
This analysis by Derek Parfit is one of the most referenced articles specifically addressing the quality of life concerns surrounding population. It is also a great demonstration of utilitarian ethical calculus and the problems with counting theoretical people.
Too many environmental organizations give the appearance that to avoid accusations of racism the white, western countries should lower their standard of living to something that would be sustainable if all 8 billion people achieved that standard. While this solution is exceedingly fair, it is also a political impossibility. There are simply too many people who will never voluntarily lower their standard of living. And in this case too many is very nearly everyone. Standard of living either goes up, or you go to war.
Any solution to our environmental and climate change issues must continue the upward trend in quality of life globally. Poorer countries can catch up and richer counties may slow their growth, but the trends must all continue upward to avoid social upheaval. Population reduction enables continued growth in quality of life while still addressing the many issues of sustainability that we face..
Overpopulation Videos
There are a number of good videos online that break down the issues surrounding overpopulation in a very informative and entertaining way. However, they tend to ultimately dismiss the issue of overpopulation as one that will either self-correct or become irrelevant dues to some optimistic future tech. They all use accurate information about the availability and impact of certain resources like food and oil, but rarely address the quality of life issue, or the possibility that some lesser-known resources will cause us problems in the future, or the general collapse of biodiversity we are witnessing.
Why Population is Actually a Problem (Video)
This video gives a detailed and nuanced breakdown of the way population issues are approached by mainstream left and right politics, especially how racists have embraced it to support anti-immigration policies. It rightly points out that population trends are already self-correcting, and that fossil fuels are the primary driver of climate change. However, this argument focuses on solving climate change to the exclusion of all the other environmental and quality of life issues caused by overpopulation. It also veers into anti-capitalism which is not a great strategy if you want to reach the billions of people who have lived their entire lives being bombarded by pro-capitalist propaganda. But that's a separate issue.
Overpopulation Facts (Video)
One of the few videos to mention the quality of life issue and it gets about 20 seconds out of an 8 minute speech. Also one of the few that is willing to say that a lower population would be ideal, not just stopping growth.
Spay and Neuter Your Pets People