If you were to remove a single technology from the modern world — to reach back into the early twentieth century and undo one invention — the one that would unmake the most of what we now take for granted is not the computer, or the internal combustion engine, or the antibiotic. It is a chemical process you have probably never heard of, perfected in a German laboratory in 1909, that produces a colorless gas with a sharp smell. Without it, roughly half the nitrogen atoms in your body would not be there.
This is not a metaphor. Through a chain of agricultural inputs that begins with synthetic ammonia and ends in the protein on your dinner table, the Haber-Bosch process is the direct source of the nitrogen that builds most of the human population's tissues. There are about eight billion of us. Roughly four billion are alive because of this one reaction.
The chemistry, briefly
Nitrogen is everywhere — about 78 percent of the atmosphere is nitrogen gas — but plants cannot use it in its atmospheric form. The triple bond that holds the two nitrogen atoms together is among the strongest in chemistry; breaking it requires either a lightning strike, certain specialized bacteria, or an industrial process operating at temperatures and pressures that did not exist anywhere on Earth before 1909.
Fritz Haber, working at the University of Karlsruhe, found that if you combined nitrogen gas and hydrogen gas at roughly 200 atmospheres of pressure and 400 degrees Celsius, in the presence of a finely divided iron catalyst, the bond would break and the atoms would recombine as ammonia. Carl Bosch, working at BASF, then spent five years figuring out how to do this at industrial scale without the reactor exploding. By 1913, the first Haber-Bosch plant in Oppau was producing thirty tons of ammonia a day.
"For the first time in history, humanity could make fertilizer from air."
What it changed
Before Haber-Bosch, nitrogen for agriculture came from three sources: animal manure, leguminous crop rotations, and the guano islands off the coast of Peru. The first two were limited by the size of the herd and the patience of the farmer. The third was finite, and in the late nineteenth century the world's largest deposits were being mined toward exhaustion. Several economists in the 1890s predicted that the global population would soon hit a hard ceiling determined by nitrogen supply.
The Haber-Bosch process broke this ceiling. The global population in 1900 was roughly 1.6 billion. It is now five times that. Almost all of the additional people are fed by synthetic nitrogen — either directly, through fertilizers that increase crop yields, or indirectly, through grain that feeds the animals we eat.
What it cost
The honest accounting of this invention is more complicated than the heroic version. Haber was a German patriot, and during the First World War he turned his expertise to the development of poison gas, personally supervising the first chlorine attack at Ypres. His wife, herself a chemist, killed herself in protest a week later. Haber went back to his lab the next day.
The plants that produced ammonia for fertilizer in peacetime were the same plants that produced explosives in war. The First World War, prolonged by industrial nitrogen, killed about seventeen million people. The Holocaust killed six million more, in chambers Zyklon B — a derivative of an insecticide Haber's lab had developed in the 1920s — even though Haber himself, a Jew, had been forced into exile by 1933 and died a year later.
This is not a moral parable. It is, more uncomfortably, what a transformative technology actually looks like in history. Haber-Bosch did not arrive cleanly. It is responsible for both more human flourishing than almost any invention in the modern record, and for some of the most concentrated horror of the same period. The two are not separable, because the molecule does not know what it is being used for.
The energy problem
Synthetic ammonia, today, accounts for roughly two percent of global energy consumption and about 1.3 percent of carbon dioxide emissions. This is a staggering figure for what is, in effect, a single chemical reaction. It is also the single most important number in the conversation about how to feed the world without cooking it.
The good news is that the reaction itself does not have to emit carbon. The hydrogen feedstock currently comes from natural gas, but it can be made from water through electrolysis — and if the electricity is clean, so is the ammonia. Several "green ammonia" plants are now under construction in Australia, Saudi Arabia, and the American Midwest, and the first commercial shipments began last year.
Whether this scales fast enough to matter for the climate is the open question. The current infrastructure is enormous, deeply optimized, and very cheap. Replacing it will cost something on the order of two trillion dollars and take twenty years. But it is, importantly, a problem whose solution is now visible. We know how to make ammonia without fossil fuel. The remaining work is engineering and finance, not invention.
Which is, in a way, the right ending to the story of Haber-Bosch. The invention was finished a century ago. What we are doing now is paying for it.