My SUV Brought Down a Tyrant!

New York Times columnist Paul Krugman has blamed the recent civil unrest in Egypt on rising food prices caused by global warming:

While several factors have contributed to soaring food prices, what really stands out is the extent to which severe weather events have disrupted agricultural production. And these severe weather events are exactly the kind of thing we’d expect to see as rising concentrations of greenhouse gases change our climate — which means that the current food price surge may be just the beginning. ...

The usual suspects will, of course, go wild over suggestions that global warming has something to do with the food crisis ...

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.

If, instead of the one degree of warming we've had over the last century, there had been one degree of cooling, would that have improved agricultural production? The answer is almost certainly no. This creates a conundrum: Krugman claims the extreme weather of a warming world is harmful to agriculture; yet, a cooling world would also decrease crop yields. The implication is that the world of 1850-1900 was a climate optimum for agricultural production - but how could anyone claim to know such a thing? Due to better technology, agricultural yields have sky-rocketed over the last 100 years. How could anyone weed through that data of changing variables and proclaim that even though yields were inferior - the late 1800s were the climate optimum for global agricultural production?

The late 19th Century had better agriculture than the Little Ice Age which preceded it (again, cooler temperatures are bad for agriculture), but it was even hotter in the Medieval Warm Period than it is today - a time when agriculture flourished. (It should be noted that all of the periods had political unrest).

There's no doubt that recent events in Egypt have been fueled by higher food prices. However, this chart shows the rise to be a blip in the post-WWII trend of declining food prices.

Do short-term weather events effect food prices? Yes. Can the recent weather events be attributed to long-term climate changes? No. Linking a warmer world to more extreme weather events is still very tendentious (and it's the key to Krugman's argument).

Will long-term climate change (yes, the climate is changing) lead to lower global agricultural yields? Unknown. Probably not. At least, there's little reason to think it will.

Is the unrest in Egypt due to climate change? Such an assertion is dubious.