Population growth and land use change
Number 3; 03/11/2023
It has been estimated that at the time cities first arose in Mesopotamia, the world population was only five million. By 1650, about 10,000 years later, the population of the world had multiplied by 100 times to five hundred million. That is only slightly lager than Boise, Idaho, whose population is the 102nd largest metropolitan area in the United States. Every state in the U.S. has more residents than the world did in 1650. In the next 337 years, the population increased by 10 times.
For more recent population comparisons, I like to think of the population when my ancestors were born. Only 150 years after1650, my great-great grandfather, Donald, was four years old in 1804 when the Earth’s population had doubled to 1 billion. Only 127 years and four generations later, I was born into a world twice that size–2 billion people. When my daughter was a born, the world’s population had nearly doubled once again; and since 1979, it has surpassed 8 billion people. That is an eight fold increase in the last 217 years.
What a short time, considering that modern Homo Sapiens evolved about 300,000 years ago, when the population was, at most, but a few thousand. The increase in numbers of humans since the evolution of Homo Sapiens is a good example of exponential growth. Today we should all be aware of the extraordinary times we live in. These accelerating, or exponential rates cannot be maintained because the limits of the ability of the Earth to support today’s population have been exceeded.
The most rapid period of population increase witnessed by everyone living today has been supported by energy from fossil fuels. And whether by the decline in cheap energy sources or by pollution of the Earth’s land, sea , air, this support will come to an end. Renewable energy cannot replace the cheap energy of today even if polluting GHG were to be returned to post World War II levels. (An explanation will be found elsewhere in this series.)
Not only has the human population grown, especially in recent decades, but so have the numbers of animals that were domesticated by humans. Paul Chefurka’s chart of the biomass of terrestrial vertebrates shows the growth of humans and their animals. In red, the biomass of humans at the beginnings of agriculture, are barely represented as a line on the graph for 10,000 BCE. But, today, the biomass of people is greater than that of all the land vertebrates on earth at the time agriculture was first practiced. The biomass of domesticated animals is now more than 40 times that of wild animals when the human population was less than five million. Wild animal biomass, shown in green, has been reduced to less than that of domesticated goats.
The decline in the population size of wild species, studied by the World Wild Life Fund, records a loss of over 60 % between 1970 and today. Most of this decline is due to land clearance, pesticide use, and other human activities. 
Insect populations have also declined dramatically. The causes of this decline are shown on the diagram below. Intensive agriculture, deforestation, urbanization, and alterations to wetlands and rivers, in other words, changes in land use in recent decades, are responsible for about 50% of the decline. The use of fertilizers and pesticides account for another 22%. The growth of the human population and related land uses have caused the decline in wild species.
Not only has wildlife suffered because of the changes in land use caused by the growth of human population, the very physical bases of nature and the Earth’s ecological and evolutionary processes have been altered by human activities. These changes have accelerated greatly in the last two centuries and have been in irreversible collapse possibly since 1950, as is shown in this diagram by Michael Dowd. I will be presenting diagrams in Report 4 that is concerned with the third of the contribution to global warming: the burning of fossil fuels.
