For millennia, the human population grew very slowly, probably about 0.04 percent per year through the eighteenth century. Population growth accelerated in the nineteenth century due to advances in health care, nutrition, and public sanitation. By 1800, the population was about 1 billion people. The rate of population growth rapidly accelerated in the 20th century, reaching about 2 percent per year in the 1960s. By 2022, the world population was nearly 8 billion.
The population growth rate is falling dramatically and now stands at about one percent per year. The dramatic decline in fertility is due to a variety of forces, including improved educational opportunities for women, lower child mortality, better access to contraception and family planning information, later age of marriage, and higher incomes. The United Nations makes forecasts of future population size based on assumptions about fertility rates and other demographic forces. Its “medium variant” forecast puts the human population stabilizing at about 11 billion people by 2100.
How will country populations change?
The population projections indicate some dramatic shifts in the ranking of countries compared to the mid-twentieth century. The United Nations projects that by 2027 India will overtake China as the world’s most populous country. Nine countries will account for the bulk of the growth: India, Nigeria, Pakistan, the Democratic Republic of the Congo, Ethiopia, the United Republic of Tanzania, Indonesia, Egypt and the United States. The population of sub-Saharan Africa is projected to double by 2050, whereas the population of Europe and North America is projected to grow by a modest 2 percent. The populations of Japan, Russia, Poland, Italy, Germany, and other nations are projected to decline over that same period.
How Much Energy?
A human adult today with moderate physical activity requires 1.5 to 5.0 GJ of food energy over the course of one year. Metabolic energy needs vary by gender, weight, age, lifestyle, physical activity, and other factors.
But how much energy do we use other than food? That depends on the quantity and type of energy services we use. Our ancestors in the late Paleolithic era (circa 15,000 years ago) used about 2 GJ per person per year in the form of fuelwood to cook meat and provide warmth. By 1850, average global primary energy consumption was about 20 GJ per person, including fuelwood, wind, flowing water, fodder for draft animals, and coal. In 2021, average per capita use in the world was about 76 GJ per capita, predominantly in the form of fossil fuels.
At a very basic level, more people mean more energy to supply them with energy services. Countries with large populations (Brazil, United States, China, India) use more energy compared to countries with small populations (Iceland, Nauru, Botswana, Belize). This suggests that if population continues to rise as the United Nations projects, more energy will be needed to support that larger population.
This poses a critical question: how do we supply additional energy that will meet the needs of two to three billion additional while simultaneously bringing climate change under control and eliminating the extreme inequities in access to safe, affordable, clean energy? We explore these questions in more detail in other articles.
Demography is not destiny
“Demography is not destiny” when it comes to energy use. Population growth and energy use do not move in lockstep.Consider the case of Canada and Uganda. Their populations are very close in total size, but Canada uses 167 times more energy than Uganda. Similarly, Qatar and the Philippines use roughly the same amount of energy, but the population of the Philippines is 38 times larger than Qatar.
The data clearly reveal large differences in per capita energy use. The average Qatari uses more than 700 GJ of energy each year; the average Filipino uses just 19 GJ per year. Clearly, there are other strong forces at work other than population size that determine how much energy a country uses.
Non-demographic factors include geography (larger countries use more energy for transport), climate (cold countries use more energy for heating), economic structure (service-based economies use less energy than manufacturing-based economies) policies such as taxation (higher energy prices encourage the efficient use of energy), and cultural factors (an emphasis on consumption increases energy use).
Energy is used to extract and process natural resources, to manufacture goods and services, and to transport them to consumers. Historically, people generally have used higher incomes to purchase more appliances, electronic devices and other goods and services; take more vacations; eat more meat and dairy; and heat/cool their home homes to warmer/colder temperatures. These decisions all increase energy use. But ultimately this is a question of lifestyle. Once basic energy services are attained, additional consumption and energy use become personal and household choices, not imperatives. Confronting climate change and eradicating inequitable life opportunities requires us to reexamine the “more is better” mantra that dominated our thinking for the past 150 years.