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Figure 1. Changes in global grain yields and global temperatures 1961-2011
Data Sources: FAO, BEST, Photo


I keep reading these claims that we're all going to starve because of global warming. People say it's going to be the death of agriculture, that increasing temperatures will cause significant drops in crop yields. Here's a typical bit of alarmism (emphasis mine):
A study by the International Food Policy Research Institute (IFPRI), indicates that climate change would hit developing countries the hardest, leading to massive decline in crop yields and production.
Whoa, a massive decline in crop yields due to increasing temperatures, sounds scary. So I thought I'd review the facts. Here is the global situation, showing the global yields of rice, corn, and wheat, along with the change in global temperature.

Now call me crazy, but what I see going on there is not a global crisis. Nor is it "massive declines". Notice that (according to BEST) the global temperature has gone up one full degree centigrade ... anyone remember any thermal crises that have resulted from that one degree of warming? Since two degrees is supposed to bring untold sorrows, where are the sorrows of one degree? Where is the lethal sea level rise? Where are the disasters? ¿Où sont les neiges d'antan? And most of all, where are the decreases in yield from that one degree of warming?

Of course, you could say that this is just because it's a global average, and not all countries produce wheat, so we wouldn't expect good agreement between global temperature and global grain production. And you might be right. So ... here's the same chart, only this time just for the US;

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Figure 2. As in FIgure 1, except for the US rather than for the whole globe.
BEST US temperature data
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Again, there is no thermal related decline in yields. According to BEST the US, like the globe, has gone up about a degree since 1960 ... where are the climate refugees? Where are the corpses? Where are the thermal catastrophes? And more to the current point, where are the declines in food production? I don't see them.

Finally, I thought "Well, maybe if I detrend all of the US data and then see how well related the change in annual temperature is to the change in annual crop yields" ... no joy there either. Below are the measurements for those relationships. The strength of a relationship between two variables is measured by something called "R squared" (written "R2"), which varies from 0.0 for no relationship between the variables, up to 1.0 for perfectly related variables. Here's the relationship of US temperature and US crop yields:

R2, US BEST Land Temperature and US Maize (corn) yield : 0.001

R2, US BEST Land Temperature and US Rice yield : 0.000

R2, US BEST Land Temperature and US Wheat yield : 0.022

In other words, no relationship at all. I gotta confess, I don't see what folks are screaming about. If you believe the BEST data, we've seen a full degree of temperature rise in the last half century, and it hasn't done us any harm - no atolls gone underwater, no millions of climate refugees, no increases in extreme weather. And through all of that temperature rise, the crop yields have kept going up. Will they reach a maximum? Assuredly they will ... but it doesn't seem like that maximum yield is going to be much affected by the temperature.

So I fear that once again we'll have to postpone Paul Ehrlich's celebration. He's been predicting the global Malthusian food crisis for decades now, to no avail. Near as I can tell, according to the Malthusian philosophers like Ehrlich, the problem is that this continued increase in crop yields works in practice, but it doesn't work in theory ...