Chapter 9 in last summer’s contrarian US Department of Energy climate report looks at how climate change will affect US agriculture. Of course by saying “will affect” we are talking about things that haven’t happened yet. And in keeping with sound historical method, the chapter starts by looking at how things have changed in the past for a sense of what tends to happen and where it seems to be tending before turning to what models say might happen in the future based on parameters programmed in to get desired results. And since there is disagreement about what has happened in the past, you can imagine how much more difficult it is to be precise about the future. Still, there are a few things that can be concluded with confidence. First, extra CO2 has always boosted plant growth so it will again. Second, farmers have had to adapt to changing conditions since the invention of agriculture and have, so they will look for ways to take advantage of the weather whenever possible. Beyond that, the experts disagree. As in, the science isn’t settled.
The chapter begins with a review of econometric studies, meaning analyses that use historical data on weather and agricultural output to try and deduce whether warming helps farmers. Initially the view was that yes, it does, based on a finding that warming was associated with elevated land values in agricultural districts. But later some other authors argued that land values reflect many influences other than agricultural output, and they examined profits on farm activity instead, on which basis they concluded that warming was bad for agriculture. But an even later study argued that the best measure was land rents in agricultural areas, because these respond more directly to changes in the value of crop production rather than other drivers of land values, and when that was used the finding swung back to warming being good for agriculture. Finally a study in France went back to looking at land values and found that oui, warming was tres bon for agriculture.
Alas reality is tricky, as Thomas Sowell observed. And as the DoE team point out, a problem with all these studies is they ignore the direct effects of CO2 and only look at how temperature might impact agriculture. So the team turned to laboratory and field studies, drawing on findings from our old friends at CO2Science.org among others. Based on studies in that archive and other evidence published by the National Bureau of Economic Research they concluded that CO2 boosts the growth of important agricultural crops.
None of which will come as a surprise to CDN readers. But then the report wasn’t written for our benefit but for the benefit of the many people out there who have never learned these things. Including a lot of those who say the science is both simple and settled yet do not know why, or sometimes that, greenhouse owners pump “carbon pollution” into their facilities to boost plant growth.
Next week: Crop modeling studies.
