TL;DR: loss of topsoil is a problem, but not a crisis. I’m unsure whether fixing it qualifies as a great opportunity for mitigating global warming.
This post will loosely resemble a review of the book Dirt: The Erosion of Civilizations, by David R. Montgomery. If you want a real review, see Colby Moorberg’s review on Goodreads.
Depletion of topsoil has been an important cause of the collapse of large civilizations. Farmers are often tempted to maximize this year’s production, at the cost of declining crop yields. When declining yields leave an empire unable to feed everyone, farmers are unwilling to adopt techniques that restore the topsoil, because doing so will temporarily decrease production further. The Mayan civilization seems to have experienced three cycles of soil-driven boom and bust lasting around 1000 years per cycle.
The modern world is different, right? Famine has been getting pretty rare:
The labor needed for farming has dropped dramatically.
Alas, it would be foolish of us to feel safe if we’re relying mainly on an extrapolation from a few recent centuries of increased food production. Much like it was foolish to rely on a few decades of pandemics being stopped at our borders, that trend could involve some lucky weather (e.g. it’s been quite a while since the central California valley had a flood that lasted for months).
The great trend in food production since Malthus’ time has been partly due to more farmland, but that trend is eroding:
How close are we to Malthusian limits? How big a disaster could we get from a combination of topsoil depletion, desertification, and climate change in the next decade or two?
The US has mostly run out of land that could easily be used as new farmland, leading to projections of peak farmland, which, like projections of peak oil, have so far tended to be slightly premature.
Here’s an overview of US land use:
Here are some numbers from Cassidy et al 2013:
Because so much of the United States calorie production goes to animal feed, only 34% of the calories produced in the US are delivered to the food system. … The US agricultural system alone could feed 1 billion additional people by shifting crop calories to direct human consumption. … we demonstrate that global calorie availability could be increased by as much as 70% (or 3.88 × 10^15 calories) by shifting crops away from animal feed and biofuels to human consumption.
The majority of calories that are grown in the US go to feed livestock that produce meat, eggs, and dairy. Barely more than 10% of those calories end up in food intended for human consumption.
Approximately 40% of US corn is used to produce ethanol. That’s basically a welfare system for farmers who grow more food than consumers are willing to buy.
In contrast, the typical civilization that collapsed due to food shortages seems to have spent its last century or two subsisting mainly on whatever grains or roots produced the most calories per acre on their farmland. Modern US appears to have much more luxury than that.
If we developed a sudden concern about starving, it sure looks like we could get by with a lot less meat and ethanol, and eat the grains and soy that would have gone into meat and ethanol.
We’d still have a fair amount of meat available from pasture land that is poorly suited for growing crops, and we’d still have some seafood. That would likely leave us with a richer diet than was normal a few centuries ago, and with more meat than most Blue Zone cultures eat.
There are many other options for handling a loss of farmland, but they either provide much smaller benefits or I’m uncertain how quickly they can be scaled up:
- vertical farming (unclear how quickly this can be scaled up; maybe needs too much electricity)
- most orchards and vineyards have room for another crop in the understory (pretty labor intensive)
- use New England farmland that was abandoned due mainly to it being too hilly to mechanize (pretty labor intensive)
- use wood to grow mushrooms / bacteria (as described in Feeding Everyone No Matter What)
- eat fewer calories: it would be healthy, but maybe unpopular enough to spark a revolution
- algae farming on seasteads (who knows how long it would take to scale up?)
- fish farming on seasteads (I’d rather discourage this because of likely substantial fish suffering)
- improve the soil via Drexlerian nanotechnology (might require $1 billion in basic research, spent fairly wisely, before companies are eager to invest in research)
I’m sure there are other decent options that I’ve overlooked.
Why do Farmers Destroy Land?
I don’t know to what extent these collapses tell us that people were being foolishly short-sighted. I presume some societies were making foolish mistakes, and others benefited from being short-sighted.
Farmland has often been dirt cheap. That means farmers sometimes benefit from reaping quick gains from land, then moving on to unused land.
There likely were situations where short-sighted exploitation of farmland enabled a society to gain enough power to conquer neighbors and take their farmland.
But there are some cases where societies were devastated by the loss of topsoil – see Easter Island.
Why don’t changes in the market value of farmland provide farmers with the right incentives to maintain or improve farmland?
Principal-agent problems are often an obstacle. Farmers often manage land that they don’t own, and the owner doesn’t have a good enough method of evaluating changes in soil quality. This might be solved with improved measurement technology – I have little intuition for how hard that would be.
It’s also somewhat common for farmers to be too poor to do anything other than maximize this year’s crop.
The large decline in interest rates over the past few decades should cause a large increase in the influence of future soil quality on farmland prices.
Up until maybe 1980, the US had enough land that clearing new farmland was at least as productive as preserving the quality of existing farmland.
Farmland prices seem to be showing an upward trend that might be enough to cause farmers to invest enough to stabilize soil quality. A recent influx of big investors also suggest increased incentives to care about the long-term trend of soil quality.
Montgomery’s book devotes two paragraphs to the CO2 implications of erosion. Those paragraphs might be more important than the rest of the book.
A third of the total carbon dioxide buildup in the atmosphere since the industrial revolution has come not from fossil fuels but from degradation of soil organic matter.
The stronger claims appear to be controversial. I haven’t found any easy way to evaluate them, or estimate the costs.
Montgomery also convinced me that deforestation has been more widespread than I realized (e.g. something like half of Iceland has lost its forest due to human activity). That suggests more room for reforestation to sequester carbon than I’d previously expected.
Maybe we could replace current ethanol subsidies with a program to stockpile food? Alas, farmers will veto such a replacement, and other voters won’t care much, for roughly the reasons that an N95 stockpile was unpopular in 2019.
How about replacing ethanol subsidies with a program that pays farmers to improve their soil quality? I suspect the time is almost ripe for that. Farmers ought to be concerned about the imminent obsolescence of fuel ethanol, due to the imminent switch to electric cars (see Tesla’s rise to a $770 billion market cap; also my Peak Fossil Fuel post from 2017). It shouldn’t be too hard to convince them to switch to a subsidy program whose importance is at less risk of erosion.
This post was rather US-centric, because that made it easier for me. Some other countries presumably face bigger risks.
I’ve also assumed increasing supplies of energy (on which farming now depends). Solar power is becoming steadily cheaper, causing accelerating production. We could substantially increase nuclear power if we wanted. Power grid failures are my main energy-related concern – some people ought to put more effort into handling those risks. Could you start an organization to handle this, or persuade an existing organization to tackle it?
There are other famine risks due to supervolcanoes, asteroid impact, and nuclear winter. So we ought to prioritize preparing for a few years of dramatic crop failures.