Earlier this month, before the downfall of Mubarak, an Egyptian taxi driver told me that food prices in Egypt had gone up four times in the last two years. If this is a fact, in a country where 40% of the population lives on less than $2 a day, then we can safely say that the inexorable rise in the cost of commodities and, among them, food, was a contributing factor in bringing Egyptian people out on the streets to demand a “reset” of their political system.

In this context, the question that Nobel laureate economist Paul Krugman addressed last week in his regular New York Times column was simple, yet profound in its implications: why is the cost of food going up so much since last summer?

As befitting any major incident investigation worth its salt, a number of demand- and supply-side causes are contributing to this worrying outcome. Exponential population growth continues in the background, of course. Breakneck-speed industrialisation in China and India, spurred on by excessive liquidity including Bernanke’s quantitative easing (QE), rapidly swells the ranks of the Asian middle class, who tend to introduce more grain-intensive meat into their diet.

On the supply side, the same Eastern industrialisation coupled with a peaking of the world’s crude oil production help to sustain very high oil prices (by historical standards) despite the OECD recessions we have just experienced. High oil prices naturally raise all food production costs. Peaking oil also led humanity to panic “solutions” such as the introduction of low-EROEI biofuels, which compete with food requirements for land and water.

And then since last summer, we’ve had the droughts and the floods, as the last and decisive supply-side factor that pushed food prices to record highs. Part of the weather story is a cyclical phenomenon known as La Nina, but increasing weather extremes are a prediction associated with global warming. 2010 was tied with 2005 as the warmest year on record, and disruptions to food production included extensive damage to crops as Moscow experienced temperatures over 40 degrees C, dry weather in Brazil, and biblical floods damaging the wheat crop in Queensland, Australia. As of this writing, Northern China is battling a drought that is threatening a large part its wheat harvest.

All these causes of high food prices have one thing in common. The rate at which we can extract resources such as oil, the extent and quality of arable topsoil, the atmosphere’s capacity to absorb our carbon emissions without altering its behaviour – all are determining factors of the carrying capacity of our planetary ecosystem, that is, they are all limits to growth.

Krugman’s conclusion was quite severe in its tone:

But the evidence does, in fact, suggest that what we’re getting now is a first taste of the disruption, economic and political, that we’ll face in a warming world. And given our failure to act on greenhouse gases, there will be much more, and much worse, to come.

Of course if we get lucky this year and we do not experience much damage to crops, together with the high prices from the previous growing seasons stimulating a little more production, we might get a temporary reprieve with food prices declining from the all-time highs. But that would not disprove Krugman’s thesis: if he is right, future periods of relief from high food costs should be shorter and shorter affairs, with higher and higher troughs for food costs.