I don't know if you were aware, but long established research shows that improving living conditions tends to reduce family size. — karl stone
Yes, I am aware of that.
The problem of population, 7-11 billion, is that it is up against an agricultural environment that will be deteriorating, even if we make some progress toward limited CO2/methane/other. Those are:
All the arable land we have is now being used for agriculture. There are no significant idle reserves. (What about northern lands becoming agricultural? The soils that are now very cold or frozen are not, and will not be suitable for agriculture. What about irrigation? All of the fresh water that is suitable for irrigation has been tapped. Drinking water has also passed its peak. The Asian glaciers are shrinking rapidly. In 50 years, the temperature in many agricultural areas will be too hot to work in for much or all of the day. (When the temperature and humidity combined make it impossible to cool off, people start dying from heat.) Fisheries productivity is in decline.
Agriculture, under the best of circumstances, is risky: too hot, too cold, too wet, too dry, too many insects, not enough bees, plant diseases, soil exhaustion, etc. There is usually enough world production to keep people fed, but an increasingly warm, erratic climate doesn't favor agriculture. Projecting enough production to feed 11 billion ignores erratic and fast climate change.
Not despairing yet? Declining hydrocarbon output: Much of high agricultural productivity depends on cheap, abundant oil and gas for chemicals, fertilizers, and fuel. We are past peak oil. We can not feed 7 billion people, maybe not 5 billion using animal traction, organic farming, and the like. We could do that at maybe 2-3 billion under good conditions. Those days are over.
Getting the population down to 2-3 billion or less will come about if the species crashes. That could happen if global warming becomes too severe in the 22nd century (only 82 years away).
I am pessimistic about all techno-fixes. I like techno-fixes. However, it does not appear that the we have the will or the political means to slam the brakes on CO2/methane/other. If we (the whole world) did have the will, the ways, and the means to abruptly cease CO2/methane/other output, we could, perhaps, solve the problem. But we don't. NO country is meeting even the modest targets set recent agreements.
Why not? Why are they not?
One reason is that major technological changes (like from horse power to machine power, like telephone, radio, television, railroads, highways, airplanes, medicine, engineering, etc. etc. etc.) require around 40 to 50 years to propagate throughout society. It isn't just behavior change; it's all sorts of changes. We have not committed to abandoning fossil fuels, so the 40-50 year change over hasn't begun.
Yes, there are solar panels and windmills here and there. But transportation in the developed world is still predicated on cars and trucks. Heating and cooling still are largely dependent on electricity from fossil fuels. A rising standard of living around the world requires more production of everything, and a lot of waste.
It isn't that I think we can not do anything; theoretically we can. But we run up against time (we waited too long) and material limitations on what is possible in a short period of time, because people generally don't worry about threats unless they are unmistakably visible -- like seeing the tornado about 3 blocks away. That's just the way we are wired.