Peak Phosphorus

Below is an excerpt from page 176 of Princeton professor Kenneth S. Deffeyes from his book “Beyond Oil, the view from Hubbert’s Peak” (2005):

Phosphate (PO4+++) is mined commercially from sedimentary rocks containing the mineral apatite, a form of calcium phosphate. The biggest phosphate producer, with the biggest remaining reserves, is Morocco. By now, you know the message: Major deposits turn out to be concentrated in odd corners of the world. The United States is in second place, with large phosphate mines in Florida and Idaho.

Why worry about phosphate supplies? Won’t we find a substitute by then? Phosphate is the backbone of DNA and RNA. The universal energy “currency” within cells is based on the conversion of ATP to ADP, adenosine triphosphate and adenosine diphosphate. Our teeth and bones are made of the mineral apatite. Substitute that. The next element below phosphorous in the chemical periodic table is arsenic. Not a promising place to start.

Phosphorus is essential to agriculture, increasing yields up to 50%, with 80% of phosphorus used in fertilizers to grow crops, and much of the rest in animal feed.

No other element can substitute and it can’t be synthesized.

Even if there’s lots of sun, water, and other elements, lack of phosphorus limits a plant or animal from using all of the other abundant resources. Therefore, it is no exaggeration to say that phosphorus is the most important limiting nutrient.

Recycling most of the phosphorus isn’t possible

Modern agriculture is practiced as if we had unlimited supplies.   Every truck load of food uses up phosphorus that will never return.

But it’s not all that easy to recycle in urban environments, which get food from far away agricultural regions.  If you do go to the trouble to extract phosphorus from urine and feces, how do you send it all back to all the places the imported food came from?  What little gets recycled now is sewage sludge dumped on nearby farms, where it accumulates, potentially over saturating the soil.  Recycling would also keep phosphorus from washing into rivers, lakes and oceans, where it leads to eutrophication.

But it’s too expensive to recycle and return the phosphorus to where it came from — that uses far too much energy, and we are on the cusp of energy shortages and oil shocks.  Nor can we mine more — that’s even more energy intensive, and often too expensive to extract even in politically stable nations.

If it wasn’t clear to people that this was a mineral we were dependent on, it became pretty clear in 2008, when global phosphorus prices went up 800%.

How much phosphorus is left and what other risks are there?

Recent estimates of peak phosphorus are 2027 (Mohr) and 2033 (Craswell), but you can find dozens of estimates, The most optimistic estimates lead to phosphorus running out within 200 years (Cordell).

Morocco has 85% of the remaining reserves (mainly in the Western Sahara). Morocco is potentially unstable, as are these five nations with another five percent of reserves: China, Algeria, Syria, Jordan, and South Africa.

Also vulnerable are the nations that need to import nearly all of their phosphorus, such as Europe, Brazil, and India. The United States has about 25 years of phosphate reserves left.

A major risk is that too much phosphorous could turn the oceans anoxic and create an extreme extinction like the Permian, but in this article from Science (Watson 2016) peak phosphorous may spare us this fate:

For the past several hundred million years, oxygen concentrations in Earth’s atmosphere have been comparatively high (1, 2). Yet, the oceans seem never to have been far from anoxia (oxygen depletion) and have occasionally suffered major oceanic anoxic events (OAEs), recognized in the rock record through accumulations of dark, organic-rich shales (3). OAEs seem to be promoted by warm climates, and some have been associated with major environmental crises and global-scale disturbances in the carbon cycle. New insights into the causes of OAEs are now emerging (4, 5). Furthermore, ocean oxygen concentrations are declining in the modern ocean (6). A full-scale OAE would take thousands of years to develop, but some of today’s processes are reminiscent of those thought to have promoted OAEs in the distant past.
…….
As to the persistence of OMZs in the oceans past and present, a simple calculation, first made by Alfred Redfield (8), suggests that the global ocean is chronically close to the edge of anoxia. When water leaves the sea surface, it carries oxygen absorbed from the atmosphere into the interior. An equivalent volume of deep water must upwell to the surface, carrying the limiting nutrient phosphate up from the deep ocean. (The deep waters must also carry up nitrate, but geochemists think of phosphate as the limiting nutrient because nitrogen can always be fixed by plankton from the atmosphere if it is in short supply.) Photosynthetic plankton then use up all the nutrients in the upwelling water, and the fixed organic matter sinks into the deep sea. There, it is respired back into inorganic carbon and nutrients by microbes, in the process consuming the oxygen supplied by the sinking water. Using the stoichiometry of carbon and nutrients now called the “Redfield ratios,” Redfield found that the amount of oxygen consumed is almost equal to that carried down by the sinking water (8).
The oxygen demand in the interior of the modern ocean is thus constrained to be close to the oxygen supply. This near-equality seems paradoxical because demand and supply are set by two apparently independent variables: Demand is governed by the amount of phosphate in the deep ocean, whereas the supply is set by the amount of atmospheric oxygen that dissolves in surface water. A little more phosphate, and much more of the ocean would be hypoxic (low in oxygen). Doubling ocean phosphate would be sufficient to bring on a full-scale ocean anoxic event.
 
Past natural events are believed to have suddenly increased the supply of phosphorus, especially the massive outpourings of magma that form large igneous provinces (LIPs). Prominent OAEs occurred at the same time as, or very shortly after, the eruption of LIPs (4, 5, 9, 10). A possible mechanism is that the fast-weathering rocks emplaced by these events increase the supply of nutrients to the oceans for thousands of years, forcing the ocean into anoxia. Once anoxia takes hold, it may be self-sustaining. Phosphorus is removed from the ocean through sedimentation, but if anoxic waters overlay these sediments they tend to leach out much of this phosphorus; in contrast, if the water is oxygenated the phosphorus stays in the sediments. Sediments in contact with anoxic water are thus an inefficient phosphorus sink and may even be a source of phosphorus to the ocean. Models suggest that once anoxia begins to spread over continental shelves and slopes, this positive feedback may drive the ocean into prolonged deoxygenation that lasts hundreds of thousands of years (see the figure) (11, 12).
Since the industrial revolution, land-use changes, agricultural runoff, and sewage discharges have more than doubled the amount of phosphorus entering the ocean via rivers (13). The coastal dead zones that have developed as a result are often lethal to animal life. However, the increase in nutrient input would need to be sustained for at least a thousand years to produce a change in phosphate levels sufficient to bring on a full-scale OAE. Whole-ocean anoxia is thus not an immediate global concern. If sustained for long enough, the deoxygenation occurring today could nevertheless have lasting negative consequences for the global environment.
On yet longer time scales, the paradox noted by Redfield may be explained by another feedback. A sustained increase in phosphate entering the ocean would increase not only anoxia but also marine productivity, causing more carbon to be buried in sediments. Carbon burial is the source of free oxygen because burial is the only process by which photosynthetically fixed carbon can escape reoxidation on a geologically short time scale. The resulting atmospheric oxygen increase would start to be significant on time scales of 100,000 years or more, eventually alleviating the ocean anoxia (see the figure). Rising molecular oxygen might also limit forest vegetation on land because of the increased prevalence of wildfire; given that forests increase the rates of weathering of continental rocks, limiting them would provide a negative feedback on the supply of phosphorus to the oceans, bringing the system back to a new steady state (14). Atmospheric oxygen and ocean phosphorus are thus linked in a network of multiple feedback loops. Negative feedbacks help to explain the longevity and stability of atmosphere and ocean composition, but some feedbacks are of opposite sign and may at times destabilize the Earth system, as during OAEs. The role of these positive feedbacks in sustaining OAEs remains an open question, however, as does a complete description of the underlying causes of modern-day deoxygenation; conceivably, natural feedbacks may act to amplify the effects of global change on ocean oxygen concentrations. j

Dary, Patrick, Phosphorus: is a paradigm shift required (Bardi 2014).

We can’t live without phosphorus: agriculture depends on it to enrich their soils. Phosphorus is second only to nitrogen as the most limiting element for plant growth.  Crop yields on 40% of the world’s arable land is limited by phosphorus availability (30). Nitrogen can be extracted from the air, but phosphorus can’t, it only exists in Earth’s crust, mainly phosphate rock converted to a soluble form for fertilizer, after which much of it is lost, 20% absorbed by plants the first years, some of it disappears in runoff, or locked in the soil in chemical forms plants can’t access.  Much of it is exported within food crops.

Production in the U.S. has been declining 4 to 5% a year since about 1980.

And like all minerals, if phosphorus ever gets very expensive, rising prices will cause a reduction in demand, and that eventually stops rising production.  Industry won’t extract resources so expensive they’re impossible to sell.  Consequently, there’s a limit to the low-grade resources the industry can exploit. Economists assume that technology will always come to the rescue, lower costs of extraction and restoring both demand and industry profits. But this is a leap of faith: technology has monetary and energy costs so there are limits to what it can do. So the phosphate rock production won’t end due to a lack of rock.  But since it depends on the energy derived from oil to extract, transform, and transport, when oil declines, it will too.

References

Bardi, Ugo. 2014. Extracted: How the Quest for Mineral Wealth Is Plundering the Planet. Chelsea Green Publishing.

Cho, Renee. 2013. Phosphorus: Essential to Life—Are We Running Out?

Cordell, D. et al. 2013. Phosphorus vulnerability: A qualitative framework for assessing the vulnerability of national and regional food systems to the multi-dimensional stressors of phosphorus scarcity. Global Environmental Change,  DOI: 10.1016/j.gloenvcha.2013.11.005

Craswell, E.T. et al. 2010. Peak phosphorus—Implications for soil productivity and global food security. Paper read at the 19th World Congress of Soil Science, Soil Solutions for a Changing World, August 1-6, Brisbane, Australia.

Huva, A. 2013.  Much Ado about Phosphorus. ReadTheScience.com

Blodget, H. 4 Dec 2012. Henry Blodget. A Genius Investor Thinks Billions Of People Are Going To Starve To Death — Here’s Why. Business Insider.

Elser, J. 20 2010.  Peak Phosphorus. It’s an essential, if underappreciated component of our daily lives, and a key link in the global food chain. And it’s running out. Foreign Policy.

Faludi, J. 25 Dec 2007.  Your Stuff: If It Isn’t Grown, It Must Be Mined. WorldChanging

Mohr, S, et al. 2013. Projections of Future Phosphorus Production. Philica.

Vaccari, D. A. June 2009. Phosphorus: A Looming Crisis. This underappreciated resource–a key part of fertilizers–is still decades from running out. But we must act now to conserve it, or future agriculture will collapse. Scientific American.

Walan, P. et al. 2014. Phosphate rock production and depletion: Regional disaggregated modeling and global implications. Resources, Conservation and Recycling, 93: 178-187.

Watson, A. J. December 23, 2016. Oceans on the edge of anoxia. Environmental crises can tip the ocean into O2 depletion. Science.

Woods, H. 3 Apr 2008. World’s phosphorus situation scares some scientists. The Coloradan.

 

 

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