Everyone is looking for someone to blame for high prices of oil and other mineral and agricultural commodities. Speculators (among others) are high on the list, followed by the Federal Reserve. While I don’t think blame is necessarily the right concept here, I have been arguing that low real interest rates have worked to raise real commodity prices through a number of channels. Each of these channels could be called “speculation,” if speculation is defined as behavior based on expectations of future prices.

A number of commentators, including Don Kohn and Paul Krugman, have argued that low interest rates and speculation cannot be the sources of the problem, because oil inventories are low. It is true that low interest rates, other things equal, should in theory increase firms’ desire to hold inventories.

US crude oil inventories do not appear to be especially low in the graph above, showing June 1998-June 2008 (from Bloomberg). But it is true that they are not especially high either.

We are talking about relatively integrated world markets, however, so it is world inventories that should matter most. According to the International Energy Agency’s Oil Market Report, oil inventories held in developed countries have been above average during most of the last year, as the next graph shows. They rose sharply in January 2008, which happens to be the month when the very aggressive cuts in US interest rates took place. These numbers are far from conclusive, but still…

The theory is meant to explain the mystery why prices of virtually all mineral and agricultural prices are high, not just oil, and in some ways fits others better. Inventories of some commodities are indeed high now. The price of gold, the last graph shown, is a good example. Here the evidence supports the theory (1) that easy monetary policy has driven up the price, and (2) that one channel is low interest rates making it more attractive to stockpile the yellow metal. But, as with oil, the biggest inventory is the one underground.

[Thanks to Pravin Chandrasekaran.]

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Fed Vice Chairman Donald L. Kohn in a speech yesterday, addressed a theory to which I am partial: the theory that low real interest rates have been a factor behind the continued rise in prices of agricultural and mineral commodities, including oil, over the last year.

The relevant excerpt: “Some observers have questioned whether the news on fundamentals affecting supply and demand in commodities markets has been sufficient to justify the sharp price increases in recent months. Some of these commentators have cited the actions of the Federal Reserve in reducing interest rates as an important consideration boosting commodity prices. To be sure, commodity prices did rise as interest rates fell. However, for many commodities, inventories have fallen to all-time lows, a development that casts doubt on the premise that speculative demand boosted by low interest rates has pushed prices above levels that would be consistent with the fundamentals of supply and demand. As interest rates in the United States fell relative to those abroad, the dollar declined, which could have boosted the prices of commodities commonly priced in dollars by reducing their cost in terms of other currencies, hence raising the amount demanded by people using those currencies. But the prices of commodities have risen substantially in terms of all currencies, not just the dollar. In sum, lower interest rates and the reduced foreign exchange value of the dollar may have played a role in the rise in the prices of oil and other commodities, but it probably has been a small one.” (Speech at the National Conference on Public Employee Retirement Systems, New Orleans, Louisiana, May 20, 2008).

As real interest rates have come down over the last year, real commodity prices have accelerated upward despite declining economic growth. (See graph, where the commodity price has been inverted so that one can see the correlation visually.)

The effect of interest rates can be demonstrated both theoretically and empirically. I have argued that the effect can come through any of three channels: inventories, production, and financial speculation.

Historically, real interest rates have had an inverse effect on oil inventories (when controlling econometrically for three other relevant factors). Nevertheless, I have to admit that inventory levels have not over the last year risen in a way that would support the theory. I thus have to rely more on the other channels of transmission to explain recent developments.

Stocks of oil held in deposits underground dwarf those held in inventories above-ground, and the decision how much to produce is subject to the same calculations trading off interest rates against expected future appreciation as apply to inventories. (The classic reference is Hotelling’s Rule.)

Apparently the Saudis have indeed deliberately decided to leave theirs in the ground. “King Abdullah, the country’s ruler, put it more bluntly: “I keep no secret from you that, when there were some new finds, I told them, ‘No, leave it in the ground, with grace from God, our children need it’.’’ FT 5/19/08. I see the interest rate as part of the Saudis’ decision how much oil to pump. Because the current rate of return on financial assets is abnormally low, they can do better by saving the oil for the future than by selling it today and investing the proceeds. Holding back production raises today’s oil price, to a point where the expected future return on oil has fallen to the same level as the interest rate. Hence the inverse effect of real interest rates on real oil prices. The same logic governs others’ decisions regarding how much copper to mine, how much forest to log, etc.

In addition to the link from world real interest rates to world real commodity prices, there is the less novel link from individual countries’ real interest rates to commodity prices expressed in their own currencies, a link that primarily passes through their exchange rates. For almost all of the eight floating-rate countries that I tested, both the US real interest rate and the local real interest rate (as a differential relative to the US rate) simultaneously had significant effects on real commodity prices. The effect is equally applicable to the United States: When the Fed eases and the dollar depreciates, the price of oil in dollars goes up quickly. This despite what many have thought in the past, that there is little effect because oil is invoiced in dollars.

It is hard to remember now, but mineral and agricultural commodities were considered passé less than ten years ago. Anyone who talked about sectors where the product was as clunky and mundane as copper, corn, and crude petroleum, was considered behind the times. In Alan Greenspan’s phrase, GDP had gotten “lighter;” the economy was becoming weightless, “dematerializing.” Agriculture and mining no longer constituted a large share of the New Economy, and did not matter much in an age dominated by ethereal digital communication, evanescent dotcoms, and externally outsourced services. The Economist magazine in a 1999 cover story forecast that oil might be headed for a price of $5 a barrel.

Since then, of course, we have seen tremendous increases in the prices of most mineral and agricultural commodities, many of them hitting records in nominal and even real terms (see graph). Oil is now well above $100 a barrel, and gold has just crossed the $1000 an ounce line.

The question is why.

There could well be merit to many of the explanations that have been offered for the rise in the price of oil. One is the “peak oil hypothesis,” and another is geopolitical uncertainty in Russia, Nigeria, Venezuela and – above all – the Gulf. Corn prices have been impacted by American subsidies for biofuel. And other special microeconomic factors are relevant in other specific sectors. But it cannot be a coincidence that mineral and agricultural prices have risen virtually across the board. Some macroeconomic explanation is called for.

The popular explanation since 2004 has been rapid growth in the world economy. The strongest growth has of course been coming from China and other recently minted manufacturing powerhouses in Asia, but the expansion has been unusually broad-based – including up to last year the United States and even a reinvigorated Europe. So growth has pushed up demand for energy, minerals, farm products, and other industrial inputs, right?

This reigning explanation now looks suspect. Since last summer the US economy has slowed down noticeably, and is probably entering a recession. Despite talk of decoupling, it is clear that other countries are also slowing down at least to some extent. In its most recent forecast, the IMF World Economic Outlook revised downward the growth rate for virtually every region, including China. The overall global growth rate for 2008 has been marked down by 1.1% (from 5.2 % in July 2007, just before the sub-prime mortgage crisis hit, to 4.1 % as of January 29, 2008). And prospects continue to deteriorate. Yet commodity prices have found their second wind over precisely this period! Up some 25% or more since August 2007, by a number of indices. So much for the growth explanation.

How to explain commodity prices up while the economy turns down? I will offer my answer in my next posting, tomorrow.