The improvement in global food supply per person in the period 1975 - 2017 was made possible by two technological advances: Haber-Bosch ammonia synthesis, that fixes atmospheric nitrogen in a form that plants can utilize, and the breeding of cereal plants that respond to applications of nitrogen, phosphorus and potassium fertilizer by increased yield - the Green Revolution. These advances have created intractable ecological problems. A return to organic agriculture would involve reducing world population to about 3 billion, and this is not feasible, despite the fertility declines in East Asia and Europe. The need for larger agricultural holdings to give farmers an income comparable to the average in the industrial and service sectors results in migration from rural to urban areas and the growth of megalopoles. The combustion of fossil fuel has resulted in a continuous rise in atmospheric carbon dioxide concentration which is probably the dominant factor in the rise in global temperature and mean sea level. Stabilizing the carbon dioxide concentration at a level below 600 parts per million by volume is not feasible; a rise in global surface temperature of over 2 degrees Celsius is almost certain. Energy production in the post-fossil era will not suffice to maintain an affluent society worldwide without a drastic fall in population.
Keywords: nutrition, nitrogen fertilizer, Green Revolution, population, environment, global warming.
Population and food supply
In the period 1975 - 2017, world population increased linearly at 83 million per year, from 4.06 billion in 1975 to 7.54 billion in 2017. The increase in 2017 was the difference between approximately 145 million births and 62 million deaths. Despite population growth, the global average daily food energy supply per person rose from 2440 kilocalories (kcal) in 1975 to 2940 kcal in 2015, an increase of 20 percent. The average in the United States is 3750 kcal, and 38 percent of the adult population is obese; in Japan the supply is 2800 kcal and the obesity rate is 5 percent; in Zambia and Haiti the supply is 1900 kcal and half the population is undernourished.
The supply of protein of animal origin is an indicator of the quality of a diet. Food of animal origin has three times the protein content per kcal of plant-based food, and animal protein has an amino-acid composition closer to human requirements than plant protein; the difference in quality is such that 100 g of animal protein is nutritionally equivalent to 140 g of plant protein. The global average supply of animal protein in 2011 was 28 g per person per day of livestock protein (from meat, milk and eggs) and 4 g marine protein (from fish, crustaceans and molluscs). The current supply of 32 g animal protein is 40 percent higher than the 22.5 g in 1975 (FAO, 2014). Livestock products supply 460 kcal per person per day, marine products 40 kcal. One kcal of livestock product requires 2.5 kcal of cereal feed and about five or six kcal of feed not edible by humans (grass, hay, alfalfa, oilseed cake and by-products of the milling, brewing, distilling and sugar industries). Livestock consume one-third of world cereal production (the annual amount of feed grain per person varies from over 400 kg in Canada and the United States to 7 kg in India), but a reduction would not benefit human nutrition, as the effective protein content of meat, milk and egg production is equal to the protein content of the grain consumed by livestock. National average animal protein supply varies from over 70 g per person per day in the United States and France to 11 g in India and less than 5 g in many African countries; it exceeds 40 g in all developed countries. Meat and fish are not essential to obtain sufficient high-quality protein, vitamins and minerals; dairy products and eggs can suffice. However, over 90 percent of the population of some Asian and African countries are lactose intolerant, and cannot dispense with meat or fish. As food of animal origin is the main source of vitamin B12, a vegan diet, which excludes all animal products, cannot provide satisfactory nutrition.
The two revolutions
Cereals are the most important class of crops for food and feed, and are cultivated on almost half the world's arable area. The rise in world cereal production since the 1960s is mainly due to two technological advances. The first is Haber-Bosch ammonia synthesis, in which atmospheric nitrogen is fixed as ammonia using natural gas or coal as feedstock. Nitrogen can be fixed as ammonia without the use of fossil fuel by combining atmospheric nitrogen with electrolytic hydrogen, but this method (used in Norway from 1929 to the 1980s) is more expensive than using natural gas. Fritz Haber was awarded the Nobel Prize in chemistry in 1918; chemical engineer Carl Bosch was awarded the Nobel Prize in 1931. Commercial production of Haber-Bosch ammonia began in 1913; consumption of nitrogen fertilizer reached 10 million metric tons in 1960 and 114 million tons in 2016. It is currently rising by 1.4 million tons per year.
The second advance is the Green Revolution that began in the late 1960s, after agronomist Norman Borlaug at the International Center for Maize and Wheat Improvement (CIMMYT) bred dwarf wheat that can carry heavier ears than traditional varieties and give much higher yields in response to increased applications of nitrogen, phosphorus and potassium fertilizer. Borlaug was awarded the Nobel Peace Prize in 1970. The first high-yielding rice variety was released by the International Rice Research Institute in 1966; the most recent is Golden Rice 2, a genetically modified plant designed to reduce vitamin A deficiency, the main cause of blindness in children in the developing countries. Maize yields began to rise rapidly in developed countries in the 1960s, the result of increasing fertilizer use on hybrid maize (first bred by Illinois farmer Lester Pfister in the 1930s). The U.S. maize yield increased from 2.6 metric tons per hectare in 1955 to 11.0 tons per hectare (175 bushels per acre) in 2016; the yield in Washington State, which has one-thousandth of the U.S. maize area, was 14.7 tons per hectare (235 bushels per acre); a maize yield of 20.5 tons per hectare (326 bushels per acre) was achieved by a Washington farmer. The rise in U.S. maize yield in recent years has made possible the large-scale conversion of maize to ethanol; in 2015, 38 percent of the U.S. maize harvest of 345 million metric tons was converted to ethanol and blended with gasoline for use as motor fuel; the protein-rich by-product (distillers' grains) is used as livestock feed.
Global cereal yield rose from 1.5 metric tons per hectare in 1960 to 3.9 tons in 2016; by 2050 the global yield could be raised to 5.0 tons per hectare by increasing the use of fertilizers, but this would not suffice to meet the growing demand for meat, milk and eggs from a larger population. The analysis of D.K. Ray et al. (2013) shows that a global maize yield of 8.9 tons per hectare, a rice yield of 5.9 tons per hectare and a wheat yield of 4.1 tons per hectare in 2050 would not suffice to meet demand, and that an additional 200 million hectares of harvested area would be needed for these three cereals alone.
The Green Revolution gave rise to great expectations, but Borlaug warned in his Nobel Prize acceptance speech that its benefits would be ephemeral if the "population monster" were not tamed. In 2000, Borlaug considered that 8 billion people could be fed in 2025, but declined to look more than 25 years ahead.
The success of the Green Revolution has created three major ecological problems: 1. Globally, less than half 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 (formation of algae) of rivers, lakes and coastal waters, thereby creating hypoxic "dead zones" in which fish cannot live. However, jellyfish thrive in hypoxic zones and give rise to serious problems. 2. Applying large amounts of nitrogen, phosphorus and potassium 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, selenium, arsenic, barium, chromium, iodine, boron, nickel and molybdenum. 3. Increase of the irrigated area by sinking tube wells has resulted in the depletion of aquifers and the lowering of groundwater tables; it is estimated that groundwater depletion in 2000-2008 contributed 0.4 mm per year to sea level rise, or 13 percent of the total rise (Konikov, 2011). It is estimated that 43 percent of the water used for crop irrigation worldwide is supplied by groundwater (Dalin et al., 2017). There are exceptions; cropland that normally does not need irrigation can be waterlogged as a result of exceptionally heavy rainfall, as in Denmark in 2017.
Population reduction?Without nitrogen fertilizer, global food production would be sufficient for less than half of the 2015 population of 7.3 billion (Ladha et al., 2016). Another method of calculation gives a similar result: In 1950, France was self-sufficient in cereals (with a production of approximately 400 kg per person), had a low incidence of undernourishment and used little nitrogen fertilizer; the population was 42 million and the arable area 20 million hectares. The ratio was thus close to 2 persons per arable hectare; if this ratio applied to the present world arable area of approximately 1500 million hectares, world population would be 3 billion. Agronomist D.J. Connor estimates the limit without using fertilizer at 3.1 billion (Connor, 2008); V. Smil estimates it at 3.2 billion (Smil, 2004).
A sustainable solution to the problem of reactive nitrogen in the environment would thus involve reducing world population to approximately 3 billion. Such a reduction is not feasible. It would mean reducing the global fertility rate (currently 2.5 children per woman) to 1.5 by 2050 and holding it at that level until 2200 (Basten et al., 2013). The proportion of the population in the 65+ age-group would rise to 35 percent (partly as a result of increased life expectancy). It is clear that a major reduction of world population cannot be achieved by fertility decline, but only by a global die-off. However, the fertility rate has fallen far below the "replacement level" of 2.1 in a number of European and Asian countries, including China and Japan.
ChinaThe population of China (excluding Taiwan, Hong Kong and Macao), 1.41 billion in 2017, is projected to peak at 1.45 billion in the early 2030s and decline to 1.0 billion by 2100 (UN, 2017). This is partly a result of the one-child policy launched in 1979 (in reality a 1.5-child policy, as in rural districts a second child was permitted if the first was female). The Chinese government abandoned the one-child policy in 2016, and replaced it by a 2-child limit. As a result, the fertility rate of 1.6 is expected to rise slightly, thereby delaying the peak population by several years.
JapanJapan's fertility rate has been 1.4 in recent years; this has resulted in an ageing and declining population. Prime Minister Shinzo Abe has stated that this is not a burden, but an incentive to boost productivity by technological innovation; he considers that Japan's population decline is "not an onus but a bonus". However, a Minister for the Promotion of Overcoming Population Decline has been appointed, with the object of preventing the population from falling below 100 million, expected to be reached soon after 2050. The 2017 projection of the Japan National Institute of Population and Social Security Research is that the population of 127 million in 2016 will decline to 88 million by 2065, when the 65+ age group will constitute 38 percent of the population. This means that there would be only 1.3 persons of working age to support each retiree. Those who believe that economic growth is more important than social cohesion advocate immigration to compensate for population decline. Japan's self-sufficiency rate in food supply in 2015 is estimated (on a calorie basis) at 39 percent. With current productivity in agriculture and fisheries, achieving self-sufficiency in food would involve reducing Japan's population to about 50 million.
In his "World population" (1936), economist Alexander Carr-Saunders wrote: "It is not possible to resist the conclusion that there is congestion of numbers in Japan, and that the further increase, which is to be anticipated….is a formidable menace". In 1935, Japan's population was 68 million, increasing at about 1 million per year. In the 1920s and 30s, tariff barriers and the "closed door" immigration policies of other countries prevented Japan from mitigating its population problem by increasing external trade or by emigration. Japan attempted to solve the problem by opening the "third door" (occupation of other countries), and launched "Operation Strike South" in 1941. Had the atomic bomb not been available, "Strike South" would have ended with "Operation Olympic" (the invasion of Kyushu) and "Operation Coronet" (the invasion of Honshu), with immense cost in American and Japanese lives. Postwar economic growth has enabled Japan to achieve a high standard of living at the cost of a high degree of dependence on food and energy imports and a government debt that reached 2.3 times GDP in 2016.
The future population peakAt the Population Summit of the World's Scientific Academies, held in New Delhi in 1993, representatives of 58 Academies agreed that "the goal should be to reach zero population growth within the lifetime of our children". Assuming that the annual global population increase will decline to zero linearly from 2017 to 2080, the population would peak at 10 billion. For every decade the peak population is reached later than 2080, the peak will increase by 0.4 billion; a 40-year delay to 2120 would thus result in a peak of about 11.5 billion. Providing a satisfactory diet for a population of 10 billion would mean an annual nitrogen fertilizer consumption of at least 170 million tons, and probably over 200 million tons. It is clear that humanity's dependence on Haber-Bosch ammonia will continue to rise until world population has peaked and the demand for food, livestock feed and biofuel has stabilized.
The return of MalthusThe overpopulation problem is global, but measures aimed at reducing population growth have to be implemented nationally. Physicist Charles Galton Darwin gives reasons for doubting whether the global population problem can be permanently solved, and points out an often overlooked fact: "The present era has been unique in that it has combined the wonders of the scientific revolution with the sudden expansion of the white races into vast almost uninhabited regions. The consequence has been that for two or three generations the Malthusian threat did really disappear". He adds that "there is little prospect that the Malthusian threat will again be overcome spontaneously in this way" (Darwin, 1952).
It is likely that Africa will be subjected to Malthusian checks in the coming decades; the combination of high fertility, low crop yields, inadequate infrastructure and insufficient capital investment in most African countries makes a decline in life expectancy probable. If Africa's population doubles to 2.5 billion in 2050, and cereal consumption per person rises to 300 kg per year (well below the current world average of 375 kg and almost double Africa's average in 2014), Africa will consume 750 million tons per year. An import of 150 million tons would reduce the production requirement to 600 million tons, three times Africa's production in 2014. Tripling grain production in 30-odd years would mean bringing the Green Revolution to all cropland that is irrigated or has adequate rainfall, and even this may not suffice without a substantial increase in the cereal area, approximately 130 million hectares in 2014. M.K. van Ittersum et al. (2016) arrive at a similar conclusion.
In 2017, the global urban population constituted 54 percent of the world population of 7.5 billion. By 2050, it is likely to constitute 66 percent of a world population of 9.8 billion (PRB, 2017). The increase in the urban population would amount to 2.4 billion.
It is too late to prevent the growth of "pathologically hypertrophied megalopoles", as Norman Borlaug called them in his Nobel Prize acceptance speech in 1970. By 2050, 50 cities are expected to have populations exceeding 10 million, of which 16 will exceed 20 million. The world's largest cities in 2050 will probably be Mumbai (Bombay), with 42 million inhabitants, followed by Delhi with 36 million, Dhaka with 35 million, Kinshasa with 35 million and Kolkata (Calcutta) with 33 million (UOIT, 2016). It is not possible to assign a limit to the population of a city, but there is a limit to the number of inhabitants per square kilometre for a healthy life, and it is certain that this number will be exceeded in the future megacities of Asia and Africa. The present population density of Mumbai is 31,000 inhabitants per square km, higher than the 28,000 of Manhattan. In Dhaka the density is 44,000 persons per square km.
Migration from rural to urban areas is necessary to increase the average size of agricultural holdings and the average income of farmers. India is an example: The average holding of India's 140 million farmers is 1.2 hectares. To raise the average holding to 15 hectares (the average of the 27 countries of the European Union), it would be necessary to reduce the number of farmers in India to 12 million. This means that over 600 million people (farmers and their families) would emigrate to urban areas. The problem in China, which has 200 million holdings with an average area of 0.65 hectares, is even greater than in India. To match the EU, the number of holdings in China would have to be reduced to 9 million.
Carbon dioxide emission and climate changeThe atmospheric concentration rose from 280 ppmv in 1800 to 407 ppmv in 2017. It is virtually certain that the recoverable reserves of fossil fuel will be utilized. Consuming the recoverable reserves would release approximately 1000 Gt carbon. Assuming that the airborne fraction remains 57 percent, atmospheric carbon dioxide concentration would increase by 270 ppmv to approximately 680 ppmv. It has been estimated that a doubling of the pre-industrial carbon dioxide concentration would increase global surface temperature by 2.2 - 3.4 degrees Celsius (Cox et al., 2018). This is generally considered "unacceptable". To keep the temperature rise below 2 degrees it would be necessary to stabilize the carbon dioxide concentration at approximately 480 ppm, thereby leaving most of the fossil fuel reserves underground. What a rapid phase-out of fossil fuel use would involve is estimated by Bardi and Sgouridis (2017). Stabilization of the carbon dioxide concentration at 480 ppmv is politically inconceivable; the required increase in investments for non-fossil energy installations would make sacrifices necessary, and this is not feasible in our growth-oriented world (Bardi, 2017).
The World Energy Council issued a report (WEC, 2013) in which two scenarios are given for global energy consumption at 10-year intervals from 2010 to 2050. The fossil carbon emission in 2010 is 8.8 Gt. In the "Jazz"(business-as-usual) scenario, the emission in 2050 is 13.3 Gt; in the "Symphony" (subsidized renewable energy) scenario the emission in 2050 is 7.9 Gt.(The carbon emission from cement production, currently 0.4 Gt per year, is not taken into account). Assuming that the airborne fraction remains 57 percent in the "Jazz" scenario, and declines to 50 percent in the "Symphony" scenario, the corresponding carbon dioxide concentrations in 2050 would be 516 ppmv and 480 ppmv respectively. It is clear that the concentration when the fossil emission reaches zero will be much higher.
At his trial, Hitler turned the political tables on the prosecution by embracing, rather than denying, his treason, which he held up as the mark of his patriotism. He pointed out the stark truism that, "High treason is the only crime that is punishable only if it fails."19 He argued that the traitors of 1918 should be held responsible for treason, but not Hitler himself, for "I do not consider myself a traitor, but rather simply a German who only wanted the best for his people." 20
In the post-fossil era, hydro, nuclear, solar and windpower will be the main sources of electricity. It is unlikely that non-fossil power plants can generate more than 30,000 TWh per year by 2100; the present global electricity generation is 24,000 TWh per year, of which one-third is non-fossil; a quadrupling of non-fossil generation will not suffice to enable 10 billion people to maintain an affluent society. Nuclear power will be indispensable in the post-fossil era; one thousand reactors, each of 1500 MW generating capacity, would contribute 12,000 TWh per year, almost five times the present nuclear output. This would make it necessary to commission 20 reactors per year, as the service life of a reactor cannot be expected to exceed 60 years.
Mean sea level has risen at a constant rate of approx. 3.4 mm per year since satellite altimetry began in 1993 (Leuliette, 2014). Sea level will probably continue to rise for centuries after fossil carbon emission has ceased; the long-term rise has been estimated at 2.3 metres per degree Celsius temperature rise during the next 2000 years (Levermann et al., 2013). Sea level rose by at least 3 metres, and probably more than 5 metres higher than the present level in the Eemian interglacial that began 130,000 years ago (Cuffey and Shawn, 2000), and lasted 15,000 years. The present Holocene interglacial may well be a replay of the Eemian, with a similar peak sea level. Sea level will fall by up to 120 metres in the next Ice Age (as it did in the last Ice Age), but this is likely to begin about 23,000 years from now (Imbrie and Imbrie, 1986) or possibly 50,000 years from now (Berger and Loutre, 2002).
World population will rise to at least 10 billion, 33 percent higher than in 2017. Atmospheric carbon dioxide concentration will probably rise to at least 600 ppm in the 22nd century, 50 percent higher than in 2017. It is not possible to say which is the greater danger, but it is unlikely that humanity will be able to extricate itself from dependence on the fossil fuel bonanza without paying a high price.
The view of almost all economists has been stated by Charles Lawton: "The general rule is that sustainable economic growth requires sustainable population growth" (Lawton, 2017). Those who hold this view fail to see that neither can be sustainable. The opposite view has been well expressed by Michael Roberts, a poet and mathematician who died in 1948: "The idealists [i.e. optimists; BG] live in a cloud-cuckoo land in which the world's area goes on expanding indefinitely, and the estate of each individual is undiminished by the multiplication of his fellows" (Roberts, 1951). The analysis presented in this article supports the view of Roberts.
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