The impact of demographic growth on the state of the biosphere and agroecosystems

Disruption of biogeochemical cycles and the Earth's carrying capacity

Working with the land directly depends on the stability of the biosphere; however, the growing needs of the population are destroying the natural cycle of substances. Humanity is facing a Malthusian crisis, where societal demands outpace the capabilities of the planet's depleting resources. In agronomy, this leads to increased pressure on soil cover, nutrient depletion, and a general loss of agroecosystem resilience.

Before the first industrial revolution, all vertebrate animals, including humans, accounted for only 1% of the consumption of organic matter produced by the biosphere. Today, humanity alone extracts more than 7% of the organic matter produced by plants and animals. At the same time, natural vegetation is losing its ability to compensate for these stresses: in the 20th century, the concentration of carbon dioxide in the atmosphere increased by 17%, yet no significant increase in phytomass occurred, and the opposite process is being observed.

Demographic growth dynamics and reproduction indicators

The source of immense pressure on natural resources has been the rapid growth of the population. Until the beginning of the 20th century, the number of Earth's inhabitants fluctuated at the level of several hundred million people due to epidemics and waves of famine. The situation was changed by the successes of agriculture and medicine: the introduction of new crops, the mechanization of tillage, the selection of livestock animals for high milk and meat productivity, as well as the discovery of the microbiological nature of diseases and the use of antibiotics.

• Biosphere organic matter consumption before the industrial revolution — 1%
• Current organic matter consumption by humanity — more than 7%
• Growth in CO2 concentration in the 20th century — 17%
• Population limit for biosphere equilibrium — 500 million people
• Annual net population growth — about 90 million people
• Projected population milestone in the 21st century — 10 billion people

The reduction in child mortality and the increase in life expectancy shifted demographic dynamics from slow growth to an era of explosive increase. The time intervals in which the planet's population added each new billion have been decreasing exponentially.

The annual net population growth is approximately 90 million people (births minus deaths), which is significantly faster than the heartbeat of a human, which performs about 38 million beats per year. According to statistical studies for 1995, the increase was 100 million inhabitants — the highest figure in history. Despite the fact that in the last decade, percentage growth rates have begun to decline, reaching the 10 billion milestone in the 21st century remains a realistic scenario.

The main factor of demographic imbalances is the total fertility rate (TFR) — the average number of children born to a woman during her lifetime. To maintain a constant population size with 100% child survival, a replacement-level fertility (RLF) of 2.0 is required. If the TFR is below 2.0, the population declines, and if it exceeds this value, it grows.

The actual situation is as follows: the TFR in highly developed countries is 1.9, i.e., slightly below the replacement level. However, their population is still growing because higher fertility in the past has resulted in a current generation that is quite numerous, and at present, despite the low TFR, the number of newborns here exceeds the number of deaths. But it is already possible to predict stabilization and a decrease in population, as the current generation of parents is aging, dying, and not being fully replaced by children. The TFR in less developed countries is 4.1. This is almost double the replacement fertility and leads to a doubling of the population in each generation. Different TFRs, after a certain time, lead to sharply different age-sex pyramids, reflecting the age and sex composition of the population. They are usually depicted as a histogram showing the number of people in each age group, usually with a five-year difference. The bars corresponding to the male half of the population are placed on one side of the graph, and the female on the other. It can be seen that the age-sex pyramid of highly developed countries looks like a column, reflecting the fact that the numbers of children, adolescents, young people, and middle-aged and elderly people are approximately the same. This is explained by the TFR value being close to the replacement level, where each age group just replaces the previous one.

At the same time, the age-sex pyramid of developing countries represents a triangle with a wide base, since the number of children born to each age group is approximately twice its own size. This results in a population dominated by youth and a relatively small proportion of middle-aged and elderly people. According to statistics, about 40% of the population in such countries is under 15 years old.

Based on the current age-sex pyramid and statistical data on the ratio of birth and death rates, one can predict the structure of the future population. It is evident that every five years, all bars shift upward by one position. The upper bars shorten, and the top one disappears as the very elderly die. A new bar appears at the bottom, corresponding to the number of people born over five years.

If the TFR remains unchanged, the age-sex pyramid of developing countries will form a triangle with an increasingly wide base, as each subsequent generation is more numerous than the previous one and produces even more numerous offspring. The age-sex pyramid of developed countries will maintain its shape.

Thus, the population of developing countries possesses demographic potential due to the current high proportion of young people, which will lead to a doubling of the population in the near future, even if fertility rates drop significantly.

World efforts in family planning have led to a significant decrease in TFR in recent decades. If we assume that this trend continues in the future, developing countries will approach the level of replacement-level fertility by 2025. But with their current demographic potential, their population will continue to grow noticeably until 2080.

Consequently, in 50–70 years, we will face rapid population growth in developing countries, whereas in highly developed countries, it will grow slowly or cease altogether. Their share of the population will account for an ever-smaller percentage of the global total, falling to 10% in 50 years compared to the current 25%. The top four most populous countries will be: India, China, Nigeria, Pakistan.

The population will also differ in its religious composition. A huge rise in Islam is expected: from 800 million Muslims in 1980 to 4.4 billion in 2100. Christianity, which dominates the modern world, will increase its number of adherents only from 1.4 to 2.2 billion people.

The faster population growth of developing countries is also indicated by indicators traditionally used by demographers – the crude birth rate (CBR) and crude death rate (CDR). These are the average number of births and deaths per 1,000 people per year. By subtracting the CDR from the CBR, the natural increase (or decrease) of the population is obtained. Growth (or decrease) rates can be expressed as a percentage: to do this, the result is divided by 10.

Current statistical data indicate that in the group of highly developed countries, the CBR is on average 15, and the CDR is 9, meaning the population growth is 0.6% per year:

15 – 9 = 6 (per 1000 people),

With a population of 1.2 billion people in the late 80s, such growth led to an annual increase of 7 million people in the developed countries. At the same time, in the group of underdeveloped countries, the CBR is 31, and the CDR is 10, which gives a growth of 2.1% per year. With a population of 3.9 billion in these countries in 1988, higher population growth rates led to an increase of approximately 83 million people annually in these countries.

Over the last two decades, Russia has experienced population depopulation (deaths exceeding births). For example, in the Tomsk region in 1993, 9,120 people were born and 13,902 died, and in the first quarter of 1998, 2,523 were born and 3,386 died. The infant mortality rate in the Russian Federation is 18 per 1,000 newborns, while in Japan it is 4.4, and in the USA it is 8. Life expectancy has decreased to 59 years, which is 10–12 years less than in developed countries. Men in the Siberian North live 22 years less, and women 14 years less, than those in Northern European countries.

The growing population of developing countries, for the sake of daily survival, depletes pastures and soil, clears forests for firewood, and performs many other environmentally reckless actions. Once fertile land is turning into desert, and this threatens the biosphere as a whole. The sustainable development we strive for requires much more than passive observation of what is happening. It requires concrete actions aimed both at reducing the birth rate and protecting the environment.