Friday, September 28, 2012

Cherry picking

We tend to focus in this blog on the major crop commodities. For starters, they provide the bulk of human and livestock calories. They also tend to have the best data to attract geeks like me. But there are plenty of other interesting crops in the world.

A few years ago my colleague Chris Field convinced me to take a look at potential effects of climate change on California’s perennial crops. One interesting aspect here in the Golden State is that growers have to make long-term commitments to crops. If they decide to plant a particular variety of almonds in a field, the chances are that it will be 20 or 30 years until they replant that same field. Trends in climate can be important for decisions today in a way that we just don’t see with a crop like corn or soybean.

To make a long story short, we looked at county weather and production data for all of the top 20 most valuable perennials, and for those with clear relationships with weather, then projected impacts for the next 50 years. Since it is a study based on past data, the usual caveats about not considering potential game-changing adaptations apply. Projected yields for four of the crops with the clearest yield-weather relationships are shown below. (More details and results for other crops are in a recently published paper here). Blue line shows mean projection, light shaded area is 5-95% confidence interval.

Most crops showed fairly small impacts of climate changes. For example, almonds are the most valuable single crop in California ($2 billion per year), and they seem to do better with warm springs (although warm winters are clearly bad). Some experiments done on orange trees also suggest some real benefits of higher CO2 for most tree crops, but we did not include CO2 effects in the study.

So overall the direct impacts of climate change on crops in California seem less important than the indirect impacts of warming and sea level rise on water supply. But there is one crop that seems especially vulnerable: cherries. Now, cherries are “only” a $100 million per year crop, putting it down at number 18 in terms of value in the state. But they are a perennial favorite (pun intended) at farmers markets in early summer. And watching how cherry growers adapt to climate change might hold some interesting lessons for other crops.

Some local reporters picked up on the cherry results, and went out to talk to local farmers. One could argue that they “cherry picked” the most pessimistic result to focus on, but I think their story does a really good job of explaining the reasons cherries are sensitive, and how farmers are noticing the changes. There are also two companion stories on water and pests that I found really interesting. Check it out at KQED's Quest website or below.

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