Every stable life form on earth has a niche where it can live without damaging or exhausting its supporting resources.
Because, people are dying from preventable over work, disease, starvation, and conflict we can conclude humankind is too big for its niche.
Because of increases in many people's consumption and increases in number of people, the problems associated with "being to big for our niche" are getting bigger.
Finally, the potential for injury to both humans and the environment, are about to greatly increase because the niche is contracting. We are:
Most of the world's human population, this century, will suffer a reduction in their quality of their lives. All but a billion, will die from disease, starvation, or conflict.
Humankind has one option for a nice future --- crawl back into its niche.
To accomplish this we need to learn four things.
1) How big is the niche today?
2) How big will this niche be in the future?
3) What changes do we have to make to fit into this contracted niche?
How do we implement these changes?
1) The way to establish a 50 million person population (near the end of the century) is to limit the number of births each year so that all the birth cohorts add up to 50 million. (e.g. if the average age at death was 100 then a birth cohort would be 500,000.)
2) The way to conflate the infrastructure (to that which efficiently supports 50 million) is planned abandonment of all living space on the earth except for selected areas where humans can efficiently produce foods, goods, and services using hydro electric power. Approximately 98% of all land area on earth will not be needed and will return to natural wilderness.
3) The way to limit conflict is to limit stratification of wellbeing. Let me suggest one plan, there may be others. Each person gets no inheritance. Each person at birth, is allocated a portion of the hydro electric commons and loses it at death. This yearly personal allocation of energy can be consumed, for heat light labor saving devices, used to purchase services, or pooled with others to undertake larger projects that create knowledge, technology, and new goods and services. Since the energy commodity is 100's of times more valuable than any other service or object, all transactions are done in energy units (The allocation is equivalent to 88 energy slaves.) All consumables are priced in energy units -- e.g. symphony tickets, housing, food, goods and services. A tax collected on each individual's energy allocation is used to maintain infrastructure, transportation, education and healthcare and other civil services. For example, a university or train, that lasts 200 years, and serves many people over several generations, is built and maintained by taxing the energy allocation of all individual's that live during that duration.
4) The 2% of the world allocated to human use must follow a sustainable design reflecting all future generations. The remaining 98% of the world is not impacted by human activity and returns to its natural state forever.