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World Population: How Did It Get So Big?

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Fritz Haber

Fritz Haber

Carl Bosch

Carl Bosch

1. The Haber-Bosch Process

As I have been writing this article, the world population has passed 6.8 billion. Today it's 11% more than what it was (6.1 billion) when the 20th Century ended - and when MIT Press published a book called Enriching the Earth: Fritz Haber, Carl Bosch, and the Transformation of World Food Production.

The book is about the process of synthesizing ammonia. Fritz Haber, a German, invented the process in 1909 and was awarded the Nobel Prize in Chemistry in 1918. Carl Bosch, another German working for the chemical company BASF, shared the Nobel Prize in 1931 for industrializing the process that Haber invented.

According to MIT Press, the Haber-Bosch process "has been of greater fundamental importance to the modern world than ... the airplane, nuclear energy, space flight, or television. The expansion of the world's population from 1.6 billion people in 1900 to today's six billion [in 2000] would not have been possible without the [industrial] synthesis of ammonia."

The synthetic ammonia produced by Haber-Bosch is a chemical compound of the elements hydrogen and nitrogen, and for our purposes the important element is nitrogen. Although nitrogen is abundant in the atmosphere as a gas, it is unusable until it has been fixed - converted into a form such as ammonia that is usable. Fixed nitrogen is of particular importance for fertilizers and munitions. But naturally fixed nitrogen is scarce. Germany used the Haber-Bosch process in World War I (1914-1918) to make synthetic nitrogen for explosives. Some believe that without Haber-Bosch, Germany would have run out of explosives in 1916 and might have had to quit the war two years before it actually did.

But we're interested in the connection between Haber-Bosch and human procreation, not human destruction. We're interested in synthetic nitrogen fertilizer.

3. Haber-Bosch and Population Growth

But by 1900, arable land around the world was pretty much maxed out, and the rhizobia working the land, bless them all, could fix only some 140 million metric tons of nitrogen a year. Thunderstorms rained down another 10 million tons of nitrogen fixed by lightning. But that was it. One hundred fifty million metric tons per year. Bacteria and lightning are nature's only nitrogen fixers. Farmers, of course, recycled what they already had as manure and compost. And nitrogen was also being extracted from nitrate mines in Chile (fossil nitrogen) and collected as guano from sea bird excrement. But by the early 1900s human population growth had its nose pressed up against the window of maximum food production.Then Fritz Haber and Carl Bosch broke the window.

Haber-Bosch worked around the limits of natural nitrogen production by manufacturing synthetic nitrogen fertilizer. Today, according to International Fertiliser Industry Association statistics, some 100 million metric tons of nitrogen produced by Haber-Bosch are applied annually to crops around the world, more than half of it to cereal crops. (See chart below.)

The increase in food production that Haber-Bosch facilitated has led to a very substantial increase in the world population. Almost all of the recent increase has occurred in less developed countries where, for many people, Haber-Bosch has meant the difference between starvation and survival. The author of Enriching the World, Professor Vaclav Smil of the University of Manitoba, estimates that "only about half of the population of the late 1990s could be fed at the generally inadequate per capita level of 1900 diets without nitrogen fertilizer." That's only three million people - what the population was in 1960. In other words, but for Haber-Busch, no more than half of today's population would be alive!


2. The Nitrogen Factor in Population Growth

Nitrogen is an essential part of amino acids and nucleic acids, and therefore of proteins and genes, in the cells of all living organisms, whether animal or vegetable. Nothing can live without it. But the nitrogen has to be fixed. Unfixed nitrogen can't be assimilated by most organisms including people. So how, we may ask, did people obtain the nitrogen required to sustain life before 1909 when Haber-Bosch was invented?

People obtain nitrogen the same way they obtain almost all their nutrients - by eating green plants or animals that eat green plants. Green plants have the unique ability to create nutrients from simple chemicals in their environment using energy that they've stored away as glucose (sugar). The glucose, in turn, is created from carbon dioxide in the air and water in the ground using sunlight as energy in a process called photosynthesis. This process of converting solar energy into biochemical energy also creates oxygen, which the plants don't need but we do - to breathe.

Green plants not only require nitrogen for their cells, as we do, but also for chlorophyll, the green pigment that absorbs the sunlight that provides the energy for photosynthesis. Then how, we ask again, did the plants get the nitrogen that they pass on to us when we eat them before Haber-Bosch was invented?

Back at the dawn of civilization, when hunter-gatherers were becoming farmers, they discovered that their main food crop - a cereal like wheat or rice or corn - depleted the fertility of their soil unless they alternated these crops with legumes such as peas, lentils, soy, alfalfa or clover. Legumes, it turns out, provide a home in their roots for soil bacterial called rhizobia that fix nitrogen on their own - one of the few organisms that can do so. The fixed nitrogen, converted by other bacteria into nitrates, fertilizes the soil and the green plants including cereals and legumes that grow on the soil.

To recap, every living organism on Earth needs nitrogen. We get ours directly or indirectly (through animals) from green plants. Green plants get theirs from the soil. And the soil gets its nitrogen from nitrates created by bacteria.

(continued in column to right →)


4. The Green Revolution and Population Growth

Quite a story, don't you think?

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Except that it turns out to be only half the story.

During the period between the two world wars, when Haber-Bosch processing plants had been converted from munitions to fertilizer and new processing plants were being built, the application of synthetic nitrogen fertilizer was limited because the crops in use during this period didn't respond as expected to the added nutrients and therefore crop yields didn't significantly increase. Professor D. Gale Johnson of the University of Chicago points out in his review of Enriching the Earth that "yields of corn and wheat in the United States were essentially the same in the late 1920s as in the late 1860s or even in 1800" and that wheat yields in England in 1918-45 were less than 10% higher than in 1832-59.

What Haber-Bosch needed was new high-yield varieties (HYVs) of crops bred to have an enhanced capacity for absorbing nitrogen.

The first HYV cereal crop was corn (maize) that was commercially developed in the U.S. in the 1930s. The improved yields from applying nitrogen fertilizer to the new corn started showing up in U.S. Department of Agriculture statistics towards the end of that decade (see arrow in chart above).

In 1943, at the urging of U.S. Vice President Henry Wallace, who was raised on an Iowa farm and knew something about agriculture, the Rockefeller Foundation set up an agricultural research station in Mexico in collaboration with the Mexican Government. The fruit of that collaboration was HYV wheat, and Mexico became a net exporter of it.

In the early 1960s the Rockefeller Foundation and Ford Foundation set up a research organization in the Philippines in cooperation with the Philippine Government. The fruit of that collaboration was HYV rice.

India began using the new wheat and rice varieties in the 1960s. The increase in food production was so spectacular, not only in that country but also in other Asian countries and in Latin America, that William Gaud, head of the U.S. Agency for International Development, coined the term Green Revolution to describe it. I worked for the agency in those days when its large Indian program was focused on developing fertilizer plants, irrigation projects and other accoutrements of the new HYV farming techniques in the hope that they would eventually replace the large wheat imports which the agency financed. One day in the 1970s, after leaving the agency, I read in The New York Times that India had become a net exporter of wheat. The efforts had not been in vain.


In 1970, Dr. Norman Borlaug, who like Henry Wallace was raised on an Iowa farm and who had a lot to do with developing the high-yielding wheat variety in Mexico and introducing it into India, was awarded the Nobel Peace Prize.

5. Afterthoughts

The Green Revolution is not without its issues. Many of them relate to the Haber-Bosch factor, particularly the use of nonrenewable and environmentally degrading sources of energy in manufacturing nitrogen fertilizer and the release of nitrogen that is not taken up by the crops into the environment.

The National Organics Program supervised by the U.S. Department of Agriculture will not certify any agricultural product as organic if it is grown with synthetic nitrogen fertilizer.


From a broader perspective, the problem with the Green Revolution, as with the Industrial Revolution in general, is that we've left out the maintenance. We've sold the many benefits of the revolution to ourselves and our families but haven't yet provided for the costs of repairing the infrastructure and developing renewable sources of energy so that these benefits will be available to our new or as yet unborn grandchildren.

Meanwhile, the world population continues to grow at a much faster rate than it ever grew before Haber-Bosch and the Green Revolution.

I look forward to your comments.

riversedge (aka Mord)


SHAFII NJAYO on May 21, 2012:


Gregorious on April 07, 2012:

A very interesting hub. I have never considered nitrogen to be such an important factor in our civilization.

louromano on March 10, 2012:

Thanks for your graphical solution. I like your teaching. interesting that although most of our atmosphere is nitrogen, it wasn't until the 20th Century that someone figured out how to turn that nitrogen into something we could use. Best regards !!

Becca on May 03, 2009:

I hate to be the rain cloud on this parade but hasn't anybody ever looked at the negative side effects of this technological advance? Yes it has saved millions of lives, but how many of those lives has it indirectly produced? Unfortunately for civilization we have come to a point where we are producing a greater population then the food source. I think that what we really need to focus on is how society has become backwards: the population, then the food. We are now having to control the amount of food based on the population instead of controlling the population based on the amount of food. I know that "population control" is considered to be an insensitive viewpoint of the world, but how will we be able to solve this problem before it is too late?

riversedge (author) from Delaware River Valley on August 22, 2008:

Me, too, Mandy.  And the new technologies are advancing at a rapid pace.  Just a month ago there appears to have been a big breakthrough at MIT in splitting water into hydrogen and oxygen and capturing the oxygen, which makes the feasibility of hydrogen fuel cells (for storing solar-created energy when the sun isn't shining or wind-created energy when the wind isn't blowing or for driving your electric car when the battery runs out) a lot closer.  See It would, of course, help if we in the U.S. could acquire the will to level the political playing field that now heavily favors the fossil fuel companies to the disadvantage of the new technologies.

Thanks for the comment.


Amanda Severn from UK on August 22, 2008:

Hi Mord. I've just read this hub and found it enthralling. It gives me hope for the human race. Just when things seem truly bleak, someone, somewhere comes up with a radical solution that changes everything. Reading hubs such as this makes me realise what huge gaps I have in my education.

Let's hope that the new technologies that will ultimately overcome our current dependance on fossil fuels, soon come on stream.

Cheers for now. Mandy

riversedge (author) from Delaware River Valley on July 12, 2008:

Big in the sense that in 1900 world population was only 1.6 billion and now, only a little over a century later, it is pushing 8 billion -- a huge increase in the rate of growth. Big in terms of sustainabiity, the sense I think you were using, is another and complicated question. For one answer, see my comment above to stormsailor. And thanks for your comments -- I'll keep writing articles if you all keep commenting.

desertclan on July 12, 2008:

Great idea, and great article. I didn't know (or remember from school if I learned it) about the Haber-Bosch process/development, and I learned something there. Whether the world population is "so big," though, I'm not sure. Without a doubt, we're going to eventually reach some sort of equilibrium point where further increases aren't sustainable with available technology, but it isn't clear to me how close we are to that assuming we can find ways to reduce our footprint (a big if). I agree with your "afterthoughts," although I would not want to hold up technological development because we don't have all the "maintenance" aspects also in place- they can't always be anticipated, but I agree that we do need to address them as we learn and identify them. Fundamentally (and perhaps naively), I believe in the ingenuity of the human race, and I think we'll find ways to solve these issues. The costs and especially the politics are our biggest obstacle, of course.I'd love to read your future articles. Keep 'em coming! Thanks for sharing these with us.

riversedge (author) from Delaware River Valley on July 11, 2008:

Very sensitive issue. Lester Brown, author of the book, Plan B 3.0: Mobilizing to Save Civilization (New York, W.W. Norton, 2008), is one of the few experts to address the issue of sustainable population (as opposed to optimal population, which is what I think you were talking about) openly. "One of the questions I am most often asked is, "How many people can the earth support?' I answer with another question: 'At what level of food consumption?'" He says that the current annual world grain harvest of 2 billion tons can support 10 billion people at the average Indian level of consumption, 5 billion people at the Italian level of consumption, or 2.5 billion people at the U.S. level of consumption. (See page 188 of the paperback edition.) Food for thought, certainly -- and many future articles.

stormsailor on July 10, 2008:

Fascinating look at how science makes a burgeoning population possible. I also like your balanced view in that we have yet to tackle the cost/consequences of this feat.

One wonders if we would have been better off capped at human population sustainability of around 1-1/2 billion in 1900. Clearly, I could well have been one of the other 5.3 billion that today wouldn't exist, but the grandchildren and future generations of the diminished population may have been better able to work with existing resources.

riversedge (author) from Delaware River Valley on July 10, 2008:

I don't mind a bit, Katie. Good luck with your teaching.

katielewis on July 10, 2008:

If you don't mind I'm going to present this to the biology classes I co-teach. Its one thing for my kiddos to hear about all these processes but to actually hear/see the results of these processes may make the information that much more meaningful. Thanks Uncle Mord!

riversedge (author) from Delaware River Valley on July 09, 2008:

A very interesting comment. Thanks. And interesting also that although most of our atmosphere is nitrogen, it wasn't until the 20th Century that someone figured out how to turn that nitrogen into something we could use, as nitrogen-fixing bacteria have been doing since time immemorial.

Bev and Jess on July 09, 2008:

Very interesting how live begins with the basic building blocks... nitrogen and hydrogen. So, it makes sense that Life needs to sustain and multiply by those same building blocks. The key to creating and sustaining anything goes back to starting from the building blocks. Re-Create the basic building is ingenious.

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