With all that’s going on in the world — from record-breaking warm spells to rapidly melting ice sheets — it’s easy to ignore something so seemingly mundane as dirt. But scientists at the University of Sheffield’s Grantham Center for Sustainable Futures suggest that we ignore dirt at our own peril.
Nearly a third of the world’s arable land has been lost over the past four decades, according to a new report, released to coincide with the Paris climate talks earlier this month. Experts at the the University of Sheffield called this soil loss “an unfolding global disaster” that directly threatens the agricultural productivity of the planet.
But soil erosion isn’t just a problem for food security — which is expected to become even more pressing as the world’s population booms and land available for food production wanes. Soil erosion is also tied to the climate, as the world’s soils represent a massive carbon storage system, containing three times the amount of carbon that is currently in the atmosphere.
“If the soil carbon reserve is not managed properly, it can easily overwhelm the atmosphere,” Rattan Lal, director of the Carbon Management and Sequestration Center at Ohio State University, told ThinkProgress in April.
The University of Sheffield report places most of the blame for soil erosion on what it calls unsustainable farming practices, which require large amounts of fertilizers and tilling to boost crop yields. Switching to a more sustainable model of intensive agriculture, the report urges, can help offset soil loss.
Right now, the report found that plowed fields lose soil to erosion at a rate 10 to 100 times greater than soil formation, meaning that the Earth is currently losing valuable land faster than it can be naturally replenished. Replenishing topsoil naturally is not a quick process — it takes about 500 years to replenish just 2.5 cm of topsoil. According to the World Wildlife Fund, about half of the world’s topsoil has been lost in the last century and a half.
“Soil is lost rapidly but replaced over millennia, and this represents one of the greatest global threats to agriculture,” University of Sheffield biology professor Duncan Cameron, co-author of the report, said in a press statement. “This is catastrophic when you think that it takes about 500 years to form 2.5 cm of topsoil under normal agricultural conditions.”
Over-plowing fields constantly disturbs top soil, exposing the microbes that live within it to oxygen and releasing its stored carbon. That, in turn, impacts soil’s ability to store more carbon. It also degrades the soil’s structural integrity, impeding its ability to absorb water and act as a buffer against floods, or store water for plants. Degraded soil can wash away more easily during extreme precipitation events, causing rivers and streams to become flooded with silt and sediment, which can impact ecosystems in the water.
Degraded soil is also less fertile than non-degraded soil in terms of agricultural productivity — a worrisome reality for a planet that is expected to need to increase its agricultural production 50 percent by 2050. According to the United Nations, 95 percent of our food comes from the soil, but about one-third of the world’s soils are currently degraded. For sub-Saharan Africa, that number jumps to about two-thirds, which the Montpellier Panel — an international group working to support national and regional agricultural development and food security priorities in sub-Saharan Africa — estimates costs the region about $68 billion per year in lost productivity. If topsoil loss is not slowed or reversed, the U.N. estimates that all of the world’s topsoil could be gone within 60 years.
In order to slow or reverse the trend of soil degradation, the University of Sheffield report suggests a few tweaks to the currently agricultural model. First, they suggest a more hands-on approach to soil management with cover crops and no-till soil, both of which can help boost soil health by keeping soil microbes from being exposed to oxygen and preserving a system of roots that keeps soil more tightly packed. The report also suggests weaning the world off of synthetic fertilizers and returning to the age-old but currently-underused tradition of applying night soil — also known as human sewage — to cropland, which the report argues can help restore nitrogen and phosphorus back to the soil.
As part of the U.N. climate talks, the French government launched a program aimed at studying the best methods for restoring soil health and aiding carbon sequestration. Dubbed “4 pour 1,000,” as a nod to the idea that a .4 percent increase in soil carbon annually would offset human emissions, the program is a partnership between the French government, agricultural development bodies like CGIAR, and several developing nations. The project hopes to sequester 25 megatons of carbon while boosting farming yields by 20 percent.
“The good thing is that no one disagrees that increasing soil carbon is good for agriculture, is good for the environment, good for food security,” CGIAR CEO Frank Rijsberman told ThinkProgress during the Paris conference. “If we can do it in a stable way, it captures carbon and reduces emissions. It can be a double or triple win.”