It's not as colorful in an action movie as invaders from other galaxies, for example, but it seems that soil erosion might be just as deadly to humans. Scientists from the University of California, Berkeley warn that human food security is at risk from the accelerating rate of soil depletion.

Humans have been depleting the soil resources of Earth steadily and alarmingly faster than the nutrients can be replenished. The top soil scientists in the country now warn us that soil erosion, together with the effects of climate change, will present a tremendous risk to global food security over the next century if this pattern does not change.

The top game-changer for the health of Earth's soil? Farming, which accelerates nutrient removal and erosion.

"Ever since humans developed agriculture, we've been transforming the planet and throwing the soil's nutrient cycle out of balance," said the paper's lead author, Ronald Amundson, a professor of environmental science, policy and management at the University of California, Berkeley. "Because the changes happen slowly, often taking two to three generations to be noticed, people are not cognizant of the geological transformation taking place."

Since the industrial revolution, human use of soil has changed rapidly, causing erosion to accelerate. Now humans are entering an age when our ability to support human nutritional needs with soil is plateauing, despite ever-increasing demands and the shortages/famine that already exist.

The paper, published today in the journal Science, describes the danger facing soil, "the living epidermis of the planet," nearly two weeks before the Global Soil Security Symposium at Texas A&M University. The symposium is part of actions surrounding the UN's declaration of 2015 as the International Year of Soils.

The "Phosphorous Cartel" of Our Shared Future

The researchers identify several looming threats to future soil security, including the supply of fertilizer. Farmers fertilize crops with three essential nutrients: phosphorous, nitrogen, and potassium. The discovery of a means to produce synthetic nitrogen from the early 1900s made significantly increased crop yields possible. This was a major support to dramatic global population growth. However, the nitrogen synthesis process is energy-intensive, so the global supply of nitrogen is dependent on the availability of fossil fuels.

In contrast, phosphorous and potassium come from minerals and rocks; these resources are not distributed throughout the world equitably as the authors point out. The United States holds only 1 to 2 percent of the world's potassium reserves, and these reserves won't last more than about three decades according to the research.

"This could create political challenges and uncertainties," Amundson says. "Morocco will soon be the largest source of phosphorous in the world, followed by China. These two countries will have a great deal of say in the distribution of those resources. Some people suggest we will see the emergence of a phosphorous cartel."

In light of current conflict over natural resources such as fossil fuels, this seems to be a realistic concern.

Climate Change and Soil

Soil, a natural mass reservoir for carbon, is also closely tied to climate change. Undisturbed soil can hold onto carbon stores for hundreds or even thousands of years. In fact, recent estimates suggest that just the top three meters of the Earth's soil now store as much as 2,300 gigatons of carbon--more carbon than in all of the world's plants and the Earth's atmosphere combined. That's equal to 2.3 trillion tons of carbon, or 4,600,000,000,000 pounds.

As long as this layer of soil stays undisturbed, carbon ratios aren't affected. But agriculture physically disrupts the soil, which then releases its carbon into the atmosphere. 50 to 70 gigatons of carbon has been released from soil into the atmosphere since the beginning of human history, according to the authors who base those numbers on the area of land used for farming worldwide.

Carbon sequestration is thought by some to be a means to fighting the effects of dangerous levels of climate change. The theory is that by retaining carbon in soil over the long-term can mitigate against ongoing emissions of greenhouse gases caused by burning fossil fuel. However, the authors warn that sequestration is not the answer-especially for losses in the Earth's polar regions which store large amounts of carbon.

"Carbon sequestration plans won't make a dent in the amount of soil released by climate change," countered Amundson. "The amount of carbon stored through sequestration would be tiny compared to the potential amount lost through global warming."

The effects of too much loss at the Earth's poles could be devastating:

"Warming those areas is like filling your freezer with food, then pulling the plug and going on vacation," said Amundson. "There will be a massive feast of bacteria feeding on the food as the plug gets pulled on the stored carbon in the frozen soil. Microbes are already starting the process of converting the carbon to CO2 and methane."

The Recycling Bin for Soil Nutrients

Because the most productive soils on the planet are already needed for agriculture, the authors argue for better management of the soils humanity depends upon.

The researchers propose that waste treatment facilities recycle potassium and phosphorus back into the soil rather than discarding these essential nutrients as part of solid waste. More efficient soil management can also curb loss of nutrients. For example, excess nitrogen is now considered a pollutant; nitrogen runoff saps oxygen from waterways, suffocating aquatic life and creating dead zones in coastal margins.

Amundson notes that it did not take too long to get people to start separating paper, glass and aluminum cans from their trash for recycling.

"We should be able to do this with soil," Amundson says. "The nutrients lost can be captured, recycled and put back into the ground. We have the skillset to recycle a lot of nutrients, but the ultimate deciders are the people who create policy. It's not a scientific problem. It's a societal problem."