When I was born, there were only 2.75 billion people around… Nowadays there are 7,2 billion. Imagine, it tripled over the course of my life, no wonder it seems a bit crowded now and then. And if I will become hundred, it will be 10 billion, 4 times as much….
How to manage that? Since the earth as a system has not changed. Except for solar radiation coming, in, its a closed system: All resources are already there, as molecules, or concentrated as ores or trees. But they don’t grow/change in total amount. In other words, the stock is fixed, and with that the capacity of the system. We can jump high or low, or stand on our heads, but that does not change. If there is any change its more in the negative way: every use leads to degradation of resources, from concentrated to diluted, slow or fast, with a lesser usability. Which is a unavoidable physical process. Only regrowable resources recover somewhat, within our lifespan, but the total decreases.
The earth contains ever more people degrading resources. But how much they use /consume per person is not a given amount. In fact thats the flexibility in the system, Although we convulsively try to sustain our way of life with the motto: equal or growing welfare” , (welfare usual in materialized form) thats against any common sense thinking. We will have to adapt our use of resources, which is the variable part of th equation, to the capacity of the closes system earth with a invariable amount of resources , a maximized potential. And its obvious that with more people the equal share becomes less.
What you could pose is, that the level of welfare is Inversely proportional to the amount of people . In other words: resources devised by people, with the counter maximized. Imagine living on a small uninhabited island. There is 1 tree . You can cut the tree, you will have wood, fro building or heating or whatever. But you will be sure there will be not another tree for the next 30 or 40 years. And if you arrive with a partner, its each half a tree. What counts for the island counts for the world as a whole.
On a small scale of a family things are quit clear: if children are born, the family has less money to spend per capita. Its somewhat hidden since the government provides tax advantages for having children , which shifts the financial burden partly to society as a whole. Society allegedly need for children, but then society is in a constant struggle to get employment for everybody. At the same time society stimulates robotizing. What I want to say is that there is constant social engineering on the side of people and humans, but at the resource side there is hardly limits set. Except nowadays its stimulated to recycle a bit. There are however people that see this connection between people and resources, In the Netherlands we have “club of 10 million”, (peacefully) striving to to go down from 17 to 10 million inhabitants . One of their motto’s: Go and Be fruitful and don’t increase in number. *
But their efforts are of a minority, which is globally the same. Regarding people and population growth, the recent book “ Countdown” by Alan Weisman provides a good global overview.  For the other side, the resources, there are also many interesting studies and calculations available. Which for example show that the past 12 years the forest area has been reduced by 1,5 million km2. That is 35 times the Netherlands… The same goes for non organic resources: for instance research by Mudd  shows that that the ore grades are declining for all metals: which implies that more has to be excavated an treated to get the same amount of pure material. The energy to process increases exponential. Which in turn faster depletes other resources like fossil fuels, which produce ever more CO2 emissions. Which requires us to build more renewable energy supply devices, like wind turbines, which require again steel…. Its a chain reaction. While the population keeps growing… See the real time clock here: http://www.worldometers.info/world-population/ .
So the counter as well as the denominator both go the wrong direction. To have an impression of our material consumption, have a look at the other counters on the home page of the same website.
And this will grow even further, our material consumption, as I analyzed in a previous article 
The use of resources can be directly connected to the availability and use of land. The space available per capita reduces, logically: When I was born, there was 5,2 hectares for each world citizen available. Now that is reduced to 1,9 hectares. (still including desserts and mountain ranges, excluding oceans) And we can strive for growth and increased welfare, but it will become less, however you look at it, sooner or later.
The only source adding to our potential, and is our escape route, is the sun, and its solar radiation, from outside our ‘island earth’ . Which comes in a space-time flux, radiation per m2 per hour, however is neither endlessly: its more or less a fixed flux, which, when unused disappears again to space ( reflected).
To use this potential requires again land in time: for production of food, energy, materials direct or indirect. And per capita that potential is reducing since land is reduced. So you could say that the quotient between total land and total people is the indicator for maximum potential welfare, without decreasing resource availability. 
That the potential currently is decreasing, ( in the for of more diluted resources) can be experienced regularly in daily life: like fine-dust levels around us increases, even threatening health. Fine-dust is a result from degradation of concentrated resources, like wheel tires wear and tear. The same goes for CO2 in the atmosphere, and many other substances.
With land as a crucial factor , we have a reference in how efficient nature is to absorb solar radiation, giving an impression for the total potential: nature has a efficiency of somewhere between 1 and 2 % in converting solar radiation. Which could indicate that for us as humans this is also the maximum, in a balanced ecosystem approach: the limit to create some ‘growth’ . There is also a historical reference for this: Its Japan during the EDO period: from around 1600 until 1860 Japan had voluntarily isolated itself from the rest of the world. And as a consequence had to rely only on its own resources within the islands borders. And by lack of other resources, solar energy became the major driver, for a largely biobased society. It has been calculated that the economical/welfare growth during that period was 0,3 % a year.  Mainly due to a 100% optimal use of land to capture solar energy for food, energy and resources. It might not seem a lot, but over longer time it can be substantial: The doubling time for growth/welfare ( from the 72 rule from economy) is in that case 240 years. Or the other way around: the population can grow by 0,3 % a year, with stable ( but not growing) welfare. Which would imply that the step from 2,75 million people ( at my birth) to 10 billion people in 2050, in fact should have lasted 480 years, so not before the year 2430. ( with of course the same welfare , that from the 1950’s)
But solar panels have much higher efficiency, I hear you ask. Yes and no. At first sight yes, the panel output is 14 % or more from the incoming radiation. But in that case the degradation of resources used for production of the panel is not included. That has to be compensated, ( the decreasing ore grades) to restore potentials, which requires land and solar radiation: space time for embodied energy ( production) . Its what I called Circular Energy ( for regeneration of stocks). If this is honestly incorporated, the efficiency drops drastically.
In the end , its the planet, divided by population, the people, that “determines our shelf life” .
The P from Profit is absolutely irrelevant in this. Is only a managerial tool, one that deals with people, but denies resources ( planet) . To express real materialized profit potential in a system the unit should be based on the quotient R/P : Resources divided by people, expressed in space( land) -time per capita .
Since we are completely neglecting this relation, we will face hard times.
( Also financial-economical…)
* Genesis 1:28 New International Version (NIV): 28 God blessed them and said to them, “Be fruitful and increase in number; fill the earth and subdue it. Rule over the fish in the sea and the birds in the sky and over every living creature that moves on the ground.”
 NGO for a 10 million dutch population: ( now 17,2)
 Countdown Alan Weisman
 forest area: http://science.sciencemag.org/content/342/6160/850
 Mudd, G., 2007, The sustainability of mining in Australia: Key production trends and their
environmental implications for the future. Research Report, October
 from factor 20 reduction to factor 20 more impact… http://www.ronaldrovers.com/?p=231
 1.7 global hectares 2013 :http://www.footprintnetwork.org/content/documents/ecological_footprint_nations/biocapacity_per_capita.html
 for a more detailed approach of space and time: www maxergy.org
Sustainability in EDO (1603-1867) , Eisuke Ishikawa ,http://www.japanfs.org/en/edo/index.html
 short article on Circular energy: http://www.ronaldrovers.com/?p=458 ; the paper Circular energy, can be found at: https://www.researchgate.net/publication/318318419_Closing_Cycles_Circular_Energy_the_missing_link