Much has been written about how the El Niño Southern Oscillation (ENSO) affects temperature and precipitation globally (these impacts are often referred to as ENSO teleconnections). In two recent studies (one on climate teleconnections, one on their impacts on crop production), my coauthors and I try to bring attention to the predictable interannual evolution of ENSO, which is often overlooked in discussions of food security although not in the climate science or climate forecasting communities. In particular we look to highlight the fact that ENSO events follow a predictable pattern in which La Niñas (cold ENSO events) only occur following El Niños, and often persist for two years. While not all El Niños develop into La Niñas, the pattern is still noteworthy, particularly when one considers the implication of La Niñas for food security in North and South America.
Here we need to be precise about a few terms. I’m going to talk about three main concepts: 1.ENSO creates global teleconnections, which means that the risks posed by ENSO are correlated in space, 2. ENSO has a characteristic multi-year evolution, which means risks posed by ENSO are correlated in time, and 3.The sign and timing of the anomalies (i.e. do good years follow bad or vice versa) are critical for food security.
So to save you some time (you are after all reading this blog post rather than the paper) I’ll skip to our conclusions. 1.ENSO poses a correlated risk across much of North and South America. This means that plentiful harvests in North America tend to coincide with good harvests in major producing regions of South America (some notable exceptions mentioned in the paper). 2.The characteristic multi-year evolution of ENSO is apparent not only in patterns of temperature and precipitation, but also in yield anomalies. While not all states are influenced by ENSO in the Americas, many of the major production areas for wheat, maize and soybeans are. And in significant portions of these major production areas there is a multi-year progression of yield anomalies attributable to ENSO. 3. El Niños bring favorable growing conditions while La Niñas increase the probability of crop failures. This point is crucial when we reconnect it to the life-cycle of ENSO (i.e. La Niñas only occur following El Niños). In other words, despite the spatial correlation in the risk (remember the global teleconnections), the temporal correlation brings a silver lining: Poor Pan-American production years are likely to occur following years of above expected production. I don’t think I need to hammer home why this is positive from the perspective of food stocks and food security.
So that’s the new analysis. Some reason to worry (largely ignored correlations in the risks posed by ENSO) and some information that may be used to improve food security. There’s obviously much more in the paper, including the importance of soil moisture for each crop, so I encourage you to give them a read!