Tuesday, November 23, 2010
I found the above map in a recent paper in PNAS. It shows average yield of all crops (in dry tons/hectare) across the globe. It makes fascinatingly clear where food comes from. You can click for a large version of this and the other maps below.
The most obvious high-level point to be taken from this map is that high crop yields are associated with development (the US, western Europe, Japan) . There is some question about how correlation runs here. Certainly, yields have increased enormously in the twentieth century with mechanization and agricultural chemistry, so development increases crop yields. However, it's likely also true that development has historically proceeded furthest and fastest in places particularly congenial to agriculture, which now thus show both high yields and high levels of development.
Overall one would guess that there is significant scope for improvements in yields in places like India and China as they continue to develop and urbanize.
It's interesting to compare the map above with one of NPP (net primary productivity - how much carbon plants fix in total). That map (from here) looks like this:
Clearly, the places where most of the NPP happens are in the tropics, whereas most of the crop yield occurs in temperate regions of moderate plant productivity. Humans have still not figured out how to exploit tropical areas for food production on anything like the scale of temperate regions, even though the former is where most of the plant growth occurs. It also makes it clear that trends in global NPP and trends in global food production may not necessarily correlate, since they are really centered in quite different places.
It's also interesting to compare the crop yield map above with the first principal component of the Palmer Drought Severity Index, which would be my guess for how the emerging trend of global warming induced drying/wetting will look:
Unfortunately, there is a lot of overlap between where humanity currently produces high-yield crops, and the places that appear to be getting drier (including southern Europe, western North America, and eastern China).
Presumably that is going to create a lot of pressure to more effectively exploit areas that we currently don't utilize very much.
Note: This post is part of the Future of Drought Series on Early Warning.