Is peak phosphorus the next global crisis? I've read claims that world reserves of phosphates, a mined resource essential in the production of agricultural fertilizer, are running out. The implications of this make global warming sound like a back-bencher in the End o' Civilization tournament. Can you, in your vast knowledge, shed any light on the subject? - Arcadia

Yes, we face the dread prospect of peak phosphorus. However, we're also looking at peak oil, peak uranium, peak coal-hell, even peak gallium, a metal used in electronics and solar cells that may have reached peak production eight years ago. The obvious question is, how much worse can things get?

Answer: a lot, maybe. Without oil, uranium, or coal we'll be short of energy, which is bad enough. But without phosphorus we'll starve.

Phosphorus is found in everything from matches to Coca-Cola, but more than 90 percent of the phosphorus we use goes to make fertilizer, where it's usually mixed with nitrogen and potassium. Phosphorus is a key component of DNA and cell structures and in plants plays an important role in leaf growth, yield, disease resistance, and overall maturity and health.

Modern agriculture is heavily dependent on fertilizer. Between 1919 and 1955, about a quarter of all improvement in U.S. crop yields was due to fertilizer. A UN study estimates every pound of fertilizer is responsible for about 10 pounds of cereal grain. You can fertilize with nitrogen and potassium alone, but at considerable cost to your harvest.

Now for the bad news: the U.S. produces a bit more than 27 million tons per year of phosphate rock, the primary source of phosphorus, and has reserves of about 1.1 billion tons. That means we'll run out in 40 years. Worldwide the situation is a little better, with about 160 million tons of annual production and 16 billion tons of reserves, enough for 100 years. While that sounds like a decent margin, the global peak may be less than 30 years away.

Another problem is that most of the planet's readily obtainable phosphorus supply is in Morocco (which sits on more than a third of proven worldwide reserves), Western Sahara, China, Jordan, and South Africa. Tradewise we're already in hock to the Arab countries and China, and phosphorus dependency will only make things worse. Even now China is imposing tariffs on its phosphorus to discourage exports. Spot phosphorus shortages have caused wild swings in price-during 2009, for example, phosphate rock sold for anywhere from $90 to $450 per ton.

Are we looking at phosphorus wars? Let's just say we may see some strategic initiatives, if history's any guide. The quest for fertilizer was behind an American land grab beginning 150 years ago, when the Guano Islands Act of 1856 empowered U.S. sailors to seize islands around the world for their deposits of nitrogen-rich bird and bat guano.

Back to your question: how does peak phosphorus rate on the panic meter? There's plenty of phosphate rock available, maybe ten times the amount we can profitably extract using today's technology. Rising prices will surely make it worth someone's while to invent better methods, and once that happens we'll be set for centuries.

For example, there's an enormous amount of phosphate rock in the continental shelf offshore. To get it, all we need are underwater robot miners and a willingness to tolerate massive environmental damage. Problem solved!

We can do a few things in the meantime. For example, no-till farming and crop terracing can reduce soil erosion, meaning we'd need less fertilizer to replace what washes away. We can fertilize with animal byproducts and manure, and human waste too. Sewage sludge contains enough phosphorus to prompt the thrifty Dutch to process it for fertilizer.

Some approaches are more radical.

One excellent source of phosphorus, it so happens, is urine. To harvest this resource, Sweden has rolled out special urine-diverting toilets, which use a partitioned bowl to send urine to storage tanks for phosphorus recovery. What's the likelihood of retrofitting 105 million American homes to store urine? At the moment, pretty low. But who knows how desperate we'll get?