Why the slowdown in agricultural productivity growth?

Two words:

Climate Change  Global Warming.

Well, there may be more to it.  Like reduced public research and pathogens like wheat stem rust.

But new research by my colleagues David Lobell and Wolfram Schlenker, along with Justin Costa-Roberts shows that warming has hurt corn and wheat yields on all continents except North America:

Farms across the planet produced 3.8 percent less corn and 5.5 percent less wheat than they could have between 1980 and 2008 thanks to rising temperatures, a new analysis estimates. These wilting yields may have contributed to the current sky-high price of food, a team of U.S. researchers reports online May 5 in Science. Climate-induced losses could have driven up prices of corn by 6.4 percent and wheat by 18.9 percent since 1980.

The article was embargoed until 2pm today, but it's already circulating.

A few other links:

Science News
Washington Post
UK Gaurdian
New Scientist

In my view, what's ominous here is that we're probably already seeing noticeable effects from climate change even though the world's biggest producer and exporter---the United States--hasn't seen any negative consequences.  Yet.  From the projections I've seen, that's mainly good luck.  It's been cooler here than in the past.  If (er... when) it warms here as projected, then we'll really feel the yield drag.

Perhaps I'm being knit picky, but I find the comparison with 1980 prices to be a strange baseline.  Prices are very sensitive to quantities.  It's not a question of where prices would be today in comparison to 1980.  It's a question of where prices would be today without the warming.

If quantities are some 5% lower than they would have been without warming, my own work on global supply and demand elasticities with Wolfram Schlenker suggests prices would be some 30% lower than without climate change.

Maybe this is a tongue-in-cheek way of being conservative.  But it just isn't right.

Update (wonkish clarification): My workhorse model here is just supply and demand.  That model tells me that, looking broadly across staple food commodities and globally in scope, the world demand elasticity is in the ballpark of 0.05 and the world supply elasticity is in the ballpark of 0.10.  To the extent that one is too big, the other on tends to be too small, and vice versa; so I'm more confident in the sum than the individual elasticities.  These numbers mean a inward shift in supply or outward shift in demand of 1% will have a 1/(0.15) or a 6.7% increase in price.  I was being a little conservative with a 6-fold larger price increase than the climate-induced quantity shift, partly because the quantity shift they estimate is a bit less than 5%.