Letter to the editor: The population problem in a nutshell
By Bernard Gilland
In the period 1975–2017, world population increased steadily at 83 million per year. The increase in 2017 was the difference between approximately 145 million births and 62 million deaths. Despite population growth, the global average daily food supply per person rose from 2440 kilocalories in 1975 to 2940 kilocalories in 2015.
Cereals are the most important crops for food and livestock feed; globally, 45 percent of the cereal harvest is consumed as food for humans and 35 percent as livestock feed; the remainder is used for industrial purposes, including biofuel, brewing, and distilling. The rise in world cereal production since the 1960s is mainly due to two technological advances. The first was Haber-Bosch ammonia synthesis, in which atmospheric nitrogen is fixed as ammonia that plants utilize for protein formation. Production of Haber-Bosch ammonia began in 1913, and consumption of nitrogen fertilizer reached 114 million metric tons in 2016. The second advance was the Green Revolution that began in the late 1960s after agronomist Norman Borlaug had bred varieties of wheat that give higher yields in response to heavier applications of nitrogen, phosphorus, and potassium fertilizer. The breeding and use of high-yielding rice and maize paralleled that of wheat. The most striking achievement of chemical agriculture is the maize yield in the U.S., which rose from 40 bushels per acre in 1950 to 175 bushels per acre in 2016.
The success of the Green Revolution created three major ecological problems:
—Globally, barely 40 percent of the applied nitrogen is taken up by the crop plants; the remainder volatilizes in the form of ammonia and nitrous oxide, a powerful greenhouse gas, or percolates to groundwater, resulting in eutrophication (the formation of algae) in rivers, lakes, and coastal waters; this creates “dead zones” in which fish cannot live.
—Applying large amounts of fertilizer to crops changes the balance between these nutrients and those needed in small or trace amounts; the latter include calcium, sulphur, magnesium, iron, manganese, copper, zinc, cobalt, boron, and selenium.
—Approximately 40 percent of global irrigation water is obtained by pumping groundwater from tube wells; this has resulted in the depletion of aquifers and the lowering of groundwater levels, thereby contributing 0.4 millimeters to the global sea level rise of 3.4 millimeters per year.
In 1950, France had a population of 42 million and 20 million hectares (50 million acres) of arable land, i.e. two persons per arable hectare. The nitrogen fertilizer application on cereals was small, and cereal production per person was about 400 kilograms per year, slightly more than the present world average. If the ratio of population to arable land were two persons per hectare on the world’s 1.5 billion arable hectares, world population would be 3 billion. Reducing world population to 3 billion would mean reducing the global average fertility rate (currently 2.5 children per woman) to 1.5 by 2050 and holding it at that level until 2200. The proportion of the global population in the 65+ age group would rise to about 35 percent. It is obvious that such a drastic population reduction is not feasible; it would mean raising the pensionable age and increasing the percentage of wages and salaries allocated to pension funds.
The population of China, currently 1.4 billion, is projected to peak at 1.45 billion around 2030 and decline to one billion by 2100. This is partly a result of the so-called one-child policy launched in 1979 (in reality a 1.5-child policy). The Chinese government replaced it by a 2-child limit in 2016, but this has had little effect on the fertility rate of 1.6. Japan has a population of 127 million and a fertility rate of 1.4; the population is projected to decline to 100 million around 2050. South Korea, Taiwan, and several European countries have fertility rates even lower than Japan’s. However, population decline in these countries will be more than offset by population growth in Africa and South Asia. The best we can hope for is a world population peak of 10 billion; this would make it necessary to increase the consumption of nitrogen fertilizer to at least 170 million tons per year, making 70 percent of the world’s population dependent on ammonia synthesis. It is difficult to believe that this can continue indefinitely. It is not possible to determine whether the inevitable rise of world population to at least 10 billion or the inevitable rise of atmospheric carbon dioxide concentration (407 parts per million in 2017, rising at 2.6 ppm per year) to over 600 parts per million will prove to be the greater danger to humanity.
Bernard Gilland
Copenhagen, Denmark
March 17, 2018
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