As you all know, wheat, along with rice, are the two most essential agricultural products used by mankind. If the price of either or both happens to spike, this will take a bigger chunk of money out of people's pockets, leaving them less money to spend on other things, thus causing a recession.
It just so happens that the real price of wheat has spiked just before or during every recent recession. This would lead one to conclude that spiking wheat prices cause recessions. Click on the following link to see a long-term chart showing real and nominal wheat prices:
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First notice the big price spike around 1973, when it reached a staggering $28 in constant 2008 dollars. It just so happens that a deep recession followed in 1974.
The next price spike occured around 1978-79. Not so coincidentally, there followed two recessions in rapid succession, one in 1979 and another in 1980-82.
There was another, smaller, price spike around 1989. Once again, we had a recession in 1990. This recession was not so deep, but that's certainly because the price of wheat did not spike so high this time.
Next there was another wheat price spike in 1996-97. It was just after that time that the Asian financial crisis hit, which was followed a few years later by a recession in the US and Europe. Coincidence? Nosiree. Surely it was caused by the spiking price of wheat. People simply had less money to spend on other things, which caused the recession.
Lastly you can see a more updated wheat price chart
here which shows the latest wheat price spike (this is a nominal chart) which peaked early last year. Once again it is not coincidental that a steep recession has followed. Surely this recession, just like all the previous ones, is being caused by the spiking price of wheat. And the bigger the price spike, the steeper the recession.
You can see a similar pattern with the other major world grain - rice. This chart
here shows that the price of rice spiked at about the same time as wheat early last year. Put both price spikes together and surely you've got a major impetus for an economic crash. Going back a bit farther on this chart
here, you can see the price of rice had spiked around 1996-97 (which preceded a recession) and prior to that in 1980-81 (which coincided with a recession).
So the only logical conclusion to derive from all this is that spiking prices of wheat and rice cause recessions.