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Comment | The graph that explains so much

Historians and anyone with half an eye on the past know that the world changed when abundant coal made industrial energy cheap, then natural gas for lighting, and again when oil replaced coal as the primary energy for transportation.

Around 1785, the British used natural gas from coal for illumination in houses and streets. Hard to imagine what a change it was from whale oil lamps and candles to a clean and relatively safe form of light. In 1816, Baltimore, Maryland, used this manufactured natural gas to become the first city in the United States to light its streets with gas. Then in 1885, Robert Bunsen’s invented the Bunsen burner that could vary the amount of air mixed with the gas stream for a cooler or hotter reaction. Once these opportunities to use natural gas for heating and cooking, manufacturing and processing plants, and boilers to generate electricity, it made sense to build pipelines to maintain supply. These were built in the 20th century.

The oil revolution happened soon after, a little over 100 years ago and almost within living memory. A retouched photograph in the library of Congress was copyrighted in 1890, showing Edwin L. Drake in Titusville, Pennsylvania, where the first commercial well was drilled in 1859 to find oil.

As with many revolutions, the effects of these energy innovations took time. It took time to build the infrastructure, the power lines, the roads, and the fertiliser factories. And time to figure out how to manufacture an engine that converts coal power into rotational energy to run a cotton mill or force steam through turbines to generate electricity.

But build these things we did. 

Energy made all sorts of innovations possible.

In 1909, German chemists Fritz Haber and Carl Bosch developed a high-temperature, energy-intensive process to synthesise plant-available nitrate from the air. The process converts atmospheric nitrogen (N2) to ammonia (NH3) by a reaction with hydrogen (H2) using a metal catalyst under high temperatures and pressures.

The primary source of hydrogen is methane from natural gas. Approximately 60% of the natural gas is used as raw material, with the remainder employed to power the synthesis process.

Crucially, this invention was scalable. By the 1920s, factories were producing ammonia on a commercial scale. One hundred years later, the Haber-Bosch process produces 230 million tonnes of ammonia annually (roughly 188 mt of nitrogen), mainly for use as a nitrogen fertiliser as ammonia itself, in the form of ammonium nitrate, and as urea. 

And so we come to the graph that explains so much

Here it is.

Source: Amundson, R., Berhe, A. A., Hopmans, J. W., Olson, C., Sztein, A. E., & Sparks, D. L. (2015). Soil and human security in the 21st century. Science, 348(6235), 1261071. We added data points for 2020 to the original graph.

It shows the rise in nitrogen fertiliser use after the invention of the Haber-Bosch process—an exponential increase in production and use.

And the parallel rise in human populations.

The growth in world population in the late 20th century mirrors the increasing use of industrially derived N fertiliser. It also follows the rise in energy use.

This correlation is not a coincidence.  

Crop production would have stalled if the energy-intensive conversion of nitrogen gas to ammonia had not occurred. If average agricultural yields had stayed constant since 1900, crop harvesting in 2000 would have required roughly four times as much cropland as was actually used. The cultivated area would have claimed over half of all ice-free land, rather than less than 15% of the total land area required today.

Humans ate fossil fuels, and there was so much to eat that we made plenty more humans.

Science source

Amundson, R., Berhe, A. A., Hopmans, J. W., Olson, C., Sztein, A. E., & Sparks, D. L. (2015). Soil and human security in the 21st century. Science, 348(6235), 1261071.

Hero image from photo by Federico Giampieri on Unsplash


Mark is an ecology nerd who was cursed with an entrepreneurial gene and a big picture view making him a rare beast, uncomfortable in the ivory towers and the disconnected silos of the public service. Despite this he has made it through a 40+ year career as a scientist and for some unknown reason still likes to read scientific papers.

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