Michael Roberts and Wolfram Schlenker have been conducting some important research on how U.S extreme heat affects agricultural yields. Their work has at least two implications. Agricultural yields are rising over time but their statistical work rejects the optimistic hypothesis that farmers are better able to "withstand" heat waves now than in the past. Intuitively, they are estimating the marginal effect of heat waves on crop yields at different points in time. If we are getting better at coping with the heat, then this negative "heat wave effect" should be converging to zero over time. They reject this claim. To quote the authors;
"Meerburg et al. argue that yields in the United States have
been trending upward and are expected to do so in the future.
We agree with this point but emphasize that we controlled
for it in our earlier analysis. Increasing state-specific
yield trends are highly significant in all of our regression specifications.
At the same time, the relative influence of extreme
heat was found to be the same in the earlier and later years
of our sample. This indicates that breeders have been successful
at raising average yields but not, so far, at significantly
improving heat tolerance. To clarify: yields are predicted to
decline 30–82% compared to what they would have been
without climate change. These predictions hold growing locations
fixed and exclude CO2 fertilization and possible future
So, let's be careful here. Will climate change "destroy" U.S agricultural yields? To answer this in 2011, we would need to extrapolate along the technological progress curve. They could use their "state-specific yield trends" but this would yield an uncertain estimate. They also assume that agriculture will not move to other land that might face less heat wave risk. They also cannot know whether technological advance will foster adaptation. The spectre of more GM crops arises. Here is one example that Google immediately handed me.
According to this article, an interesting intellectual property rights issue could break out. The LDCs have the knowledge about how to handle the heat.
"Vandana Shiva, a veteran environmentalist and founder of the Research Foundation for Science, Technology and Ecology – a New Delhi-based NGO – says the climate-ready genes companies are claiming as their own invention already exist and that local farmers are familiar with the varieties in which they appear.
Activists say that companies are collecting seeds from parts of the world with extreme climatic conditions in the assumption that seeds there will possess the desired genetic traits. Then they map the genome of these varieties to identify genes or gene sequences that increase a plant’s tolerance to a certain environmental stress. The companies then develop a way of transferring the identified gene sequences in a transgenic plant, or a method to over-express the trait in the same plant.
“Farmers in India have long known and used flood-resistant, drought-resistant, cold-resistant and heat-resistant seeds to adapt to local climatic conditions,” says Shiva. “Patents on these traits to multinational companies deny the innovation embodied in indigenous knowledge.”
As I discuss in Climatopolis, globalization (in this case of ideas) is a friend of adaptation. While I deeply respect the Roberts and Schlenker work, such backwards looking historical work cannot foresee how technological advance and diffusion of existing ideas will help us to adapt to increased intensity of heat waves. We have many adjustment margins; storage, trade, agricultural migration, innovation, diffusion. What is the probability that all of these strategies fail given that we are already aware that we face a potential problem. So, the research conducted by these authors acts as an "early warning" indicator and this allows us to escape.