Wednesday, September 28, 2011
2011 seems to have been a slightly crazy year weather-wise. For example, Climate Progress notes that there have already been more FEMA declared disasters in 2011 than in any prior year, with three months still to go. Between tornadoes and floods in the midwest, droughts in Texas, and hurricanes and tropical storms on the East Coast, the weather has been in the news a lot. I was curious to know whether this showed up in a big way in crop yield data (since effects on crop yields are presumably the primary way that climate change might seriously threaten civilization).
Of the three big field crops, the 2011 yield data are available from NASS for corn and soybeans, but not yet for wheat. The raw yield data are above. You can see that 2011 is a bit of a jog down but doesn't look like a marked departure from trend. My assumption is that generally the trend is dominated by improvements in agricultural technology, while the year-to-year noise is mainly due to weather.
To get a clearer idea of the context I constructed a variable which consists of the percentage change of this year relative to the average of the prior ten years. That looks like this:
Prior to around 1940 corn yields were pretty flat and so this index fluctuates around zero with 10-20% fluctuations being pretty common. After that, yields have been improving so the average is not zero but positive - this year is typically better than the average of the past ten - but fluctuations continue to be large. In particular, 2011 is not the worst downturn in yield in the post 1940 era in either crop - four or five other years are worse. However, it certainly was a worse performance than average.
So at the moment there doesn't seem to be much evidence for the proposition that the weather is getting bad enough to present a serious threat to the US food supply. Not to say it couldn't in future.