1. What does “a lot” of people look like
What does “a lot” of people look like. This picture taken in Washington when Present Barak Obama was elected for his second term represents thousands. Relative to the population of America, or on earth, this is a very minor fraction.
How many people are there on Earth today?

2. This is a rough estimate of both data and projections.
Human populations have historically been relatively low (significantly less than 1 billion) since the dawn of humanity up to 5 million years ago.
In the last 200 years the human population has seen an exponential growth to over 7 billion people. Despite our perception of major world events such as the rise and fall of empires, world wars, natural disasters, etc., these events are barely visible if even visible at all on the graph of human population growth.
As with all species, as access to resources increases, the population increases. The agricultural, industrial, technological and medical revolutions are the main contributors to this exponential increase.
Notice that the predicted trend of increase is slowing down toward We will return to this idea soon…

3. Here is our first clue as to why the human population growth rate is slowing down.
Today, we are the only known species on earth that has a decreased reproductive rate as access to resources increases. The graph above plots the fertility rates of most countries in the world against their GDP per capita on a logarithmic scale. The trend is clear and dramatic.

4. Demographic Transition Model
Humans seem to follow an observable pattern of SOCIAL progress that results in a leveling of population growth.
The most primitive human condition before the technological revolutions of the past 200 years showed a high death rate, which necessitated a high birth rate. Few populations today still live in this way, untouched by modern societal advances in survival. As societies progressed out of this condition, the first thing to change was usually the death rate. Stage two is marked by birth rates remaining high, but death rates decreasing. This results in exponential population growth.
Soon it becomes a burden to have a high death rate if survival rates remain high. Stage three sees people CHOOSING to have fewer children and birth rates decreasing. This results in a slowing of the exponential population growth trend.
Stage 4 is marked by the birth rate meeting closely with the death rate. At this stage, population growth slows dramatically and may eventually stop. The majority of the developed world currently displays a stage 4 population growth trend.
There is uncertainty about what comes next. Some countries like Germany have begun to see a net decrease in their population. This may be a fifth stage of the demographic transition model.
Remember, the demographic transition model does NOT factor in environmental factors. This is a SOCIAL phenomenon. It is observed time and again in real nations throughout the world.

5. The goal then to slow or stop population growth must be to move people through the demographic transition model as quickly as possible. We are now studying which factors accelerate the move fastest from stages 2 and 3 up to stage 4.
Much evidence suggests that one of the single most important factors in achieving this is the education and empowerment of people, particularly of WOMEN.
Observe the correlation between population growth rates and female literacy rates in the graph above.

6. This means that SOCIAL JUSTICE projects could be among the most important factors for slowing population growth to attain a sustainable population.
*Note – Moving to stage 4 of demographic transition model necessitates increasing the average ecological footprint. This means that it may be of equal importance not only to help countries develop, but to do so using sustainable technology and with an environmental conscience. It seems imperative to both slow population growth while at the same time reducing the ecological footprint of developed nations.

7. What do the experts say about the future of the human population?
Predicting the future

8. This shows the range of predictions produced by the United Nations about what may happen to the human population. The “most likely” scenarios are represented between the red and green lines. This means that by 2050, the UN predicts between 9 and 12 billion people will live on Earth.
It is important to note that these predictions are almost exclusively based on SOCIAL factors such as the demographic transition model. These do not account for the potential limits of Earth’s resources.
The new question to ask is, CAN THE EARTH SUPPORT 9-12 BILLION PEOPLE?
Predictions up to the year 2100 are very difficult to make, but one can be certain that Earth would not be able to support the constant fertility (purple), or high fertility (red) scenarios.

9. It is important to consider more than just population growth:
Population growth need to be addressed in developing countries since the majority of new people on earth with come from countries in stages 2-3
Even though the number of people in industrialized countries (stage 4) remains relatively constant (or may shrink), their resource consumption per person is dramatically higher than those in developing countries.
Slowed population growth in this way may not help stay below carrying capacity if developed nations use resources unsustainably.

10. Population change between 2010 and 2100 by major region (millions)
The UN predicts that the vast majority of population growth will come from Africa in the next 100 years
Notice the net decrease in Europe.

11. Population by Total Fertility (millions)
We can already clearly see a significant decrease in the number of births per woman from 1950 to If current rates of social progress continue, by 2050 the vast majority of the world will be at a replacement population.
Again, the goal is to accelerate this process as much as possible.

12. With fewer babies being born, the average age of the population has increased

13. The aging of the population will continue and the average life expectancy may rise.

14. Canada’s population is mostly affected today by immigration.
We have already showed a leveling of our population into late Stage 4 and perhaps early stage 5.
As seen in the second graph, the population in Canada is aging quickly

15. Here we can clearly see that Canada is currently below a replacement fertility rate. This indicates that a stable or growing population is reflective of immigration rather than fertility. It is predicted that we will level at a replacement fertility rate in the future.

16. We are living longer than ever before and the predicted increase in life expectancy shows a steep rise.

17. WHAT ABOUT THE LIMITATIONS OF THE EARTH!?!?
CAN THE EARTH SUPPORT 9-12 BILLION PEOPLE?
The question is, what is the “carrying capacity” of the Earth. In other words, what is the maximum population that the earth can support sustainably.
The answer is complicated.
Nobody knows or can accurately predict this number
It depends largely on how much we consume per person (the size of our ecological footprint)
It depends on the rates of degradation vs replenishing of the Earth’s resources (sustainable use)
There are many possible outcomes for the future in terms of environmental factors as shown in the graphs in this slide.
Technology could lead to an ever increasing carrying capacity (very unlikely)
The population levels at or below carrying capacity
We exceed carrying capacity, deplete the Earth’s resources, but stabilize at a new sustainable population
We dramatically overshoot carrying capacity and significantly deplete the Earth’s resources. This leads to a major population crash due to shortages and an impoverished environment.

18. The greater the overshoot, the more dramatic the depletion of the resources. This lowers carrying capacity and leads to a population crash due to shortages. The steeper our approach to carrying capacity the larger the overshoot would be.

19. Ideally we level the population below carrying capacity which means we maintain a sustainable population and rate of resource consumption.

20. HOW CLOSE ARE WE TO Carrying capacity?
What would you expect to see if you were near, at, or above carrying capacity?
Near = nothing (if carrying capacity is not reached, there is an excess of available resources)
At = nothing (this is the maximum stress on resources, but is not exceeding it overall… you may see some key resources depleting while others are not)
Above = depletion of resources
HOW CLOSE ARE WE TO Carrying capacity?

21. The water table on a global scale is significantly depleting
The water table on a global scale is significantly depleting. This is primarily linked to its use in agriculture.

22. Almost all of the arable lands of the world are showing signs of soil degradation, largely linked to overuse of synthetic fertilizers, and many complex factors leading to desertification.

23. Higher resolution map of soil degradation
Source: Food and Agriculture Organization of the United Nations (

24. Food and Agriculture Organization of the United Nations (2012)
Around the year 2000, we peaked in the number of fish being fished from the oceans. This is not for lack of trying, but due to rampant overfishing. Fish stocks are heavily depleted.
Many of us have not noticed because we have replaced the deficit with fish farming which tends to be largely inefficient, highly polluting and generally unsustainable.
Food and Agriculture Organization of the United Nations (2012)

25. Food and Agriculture Organization of the United Nations (2012)
The depletion of fish in the oceans is getting worse, not better. The number of fully exploited and overexploited fisheries are still on the rise.
Food and Agriculture Organization of the United Nations (2012)

26. Nearly ever major coral reef on Earth (these are the most biodiverse ecosystems in the oceans) are showing significant bleaching. This means that the corals (and subsequently the plethora of species dependent on it) are dying. This is largely caused the acidification of the oceans as a result of anthropogenic CO2 levels in the atmosphere and by poor management of tourism. More atmospheric CO2 means that more of it dissolves into the oceans as carbonic acid.

27. International Panel on Climate Change (2012)
The climate is changing. Global warming is a scientifically confirmed phenomenon caused by human activity.
International Panel on Climate Change (2012)

28. Major important bodies of water like Lake Chad have dried up and disappeared. Deserts are expanding. Many attribute a large amount of this change to human caused climate change.

29. Arctic sea ice coverage is on a steady decline

30. Non renewable energy sources (many of which produce greenhouse gases) are depleting while energy demand is increasing.

31. Here we can see the world’s increasing energy demand
Here we can see the world’s increasing energy demand. The proportion of energy consumption from fossil fuels has increased since 1990.

32. What Factors Influence the Carrying Capacity of Earth?
The picture is becoming increasingly more clear. Biologists believe that we are currently living through the largest and most rapid mass extinction of species in Earth’s history and it is cause by human activity.
We are either at or already over carrying capacity at 7 billion people if we continue to live as we do today.
There are several ways we can increase the carrying capacity of the Earth to have a chance at a sustainable future.
Reduce the resource consumption per person in the developed world.
Develop and use more efficient and sustainable technologies and agricultural practices.
Invest heavily in meaningful social justice projects to accelerate the movement of stage 2 and 3 countries through the demographic transition model to slow population growth
Protect, and rehabilitate as much of the natural world as possible.