This is a guest postย on the climate.gov ENSO blog by Weston Anderson (@HydroClim) who is an assistant research scientist with theย Earth System Science Interdisciplinary Centerย at the University of Maryland and NASA Goddard Space Flight Center, where he works with theย Famine Early Warning Systemย team.
A couple of weeks ago, NOAA issued aย La Niรฑa Watchย based on the possible development of a La Niรฑa this fall that could persist through Northern Hemisphere winter 2021-22. At times like this, we climate scientists spend a great deal of time discussing how ENSO will affect precipitation and temperature, but we often neglect discussion of what those changes will mean for vegetation and crops. Thatโs a mistake.
As a scientific community, weโre doing a lackluster job of using what we already know about ENSO (El Niรฑo/Southern Oscillation, the entire El Niรฑo-La Niรฑa system) to monitor and predict global patterns of crop yield surpluses and deficits. If I had to give us a grade, Iโd say we get a C+. That may sound harsh, but remember that in the 1980s we already understood many of the ways that ENSO affects the global atmospheric circulation. By the 1990s, we had connected ENSO to crop yields in many parts of the world (see references at the bottom of this post).
And yet, for over 20 years afterward, despite that meticulous study of how ENSO affects global precipitation, many scientists continued to focus on how ENSO impacts crop yields atย regionalย levels while ignoring the question of how ENSO impacts crop yield anomalies onย globalย scales. We did this even as strong ENSO events determined the spatial pattern of crop yields on nearly every continent in some years. But it wasnโt until after 2010 that we started to seriously study the question (e.g. Iizumi et al., 2014). We failed to see the forest for the trees.
Our Food System is Global
Why does it matter if thereโs any kind of pattern to global crop yield anomalies in ENSO years? To understand that, weโll need to take a quick detour to discuss our global food system.
When I say the โglobal food system,โ Iโm referring to the fact that roughly a quarter of all calories consumed by humans are traded internationally today. This is a marked increase from 30-40 years ago, prior to widespread agricultural trade liberalization. While more people have access to an adequate number of calories today than ever before, people are increasingly reliant on global trade for that access (1).
Relying on internationally traded food is not necessarily a bad thing, itโs simply a different food system than one in which you rely on food produced entirely in your immediate region. One benefit of a global food system is that by geographically distributing crop production, your access to a crop isnโt necessarily wiped out by any single drought.ย For example, one country may depend on another country, like Australia, to provide them enough wheat. If Australia doesnโt produce enough wheat due to a poor harvest, then that country can get their wheat from somewhere else, like Argentina. However, this stability assumes that major wheat-producing countries like Australia and Argentina wonโt simultaneously have poor harvests.
Perhaps itโs a good time to focus on that forest again.
ENSO is a control freak
The assumed independence of crop yields in distant breadbasket regions can break down during ENSO events. As I mentioned before, we know that ENSO organizes precipitation, temperature, and cloud cover on global scales in many seasons, so itโs only logical that it likewise affects crop yields (2). And by influencing the growing season climate to be more or less favorable, ENSO is picking agricultural winners and losers.
So how widespread is theย influence of ENSO? After all, many crops are grown in Northern Hemisphere summer, when ENSO tends to have weaker amplitude and a weaker influence on the global climate. Well, for better or worse, ENSO is estimated to affect yields on over a quarter of global croplands. And while it doesnโt affect crop yields every year, it can have an outsized influence in certain years when ENSO is particularly prominent relative to other weather and climate patterns (3). The massiveย El Niรฑo of 1982โ83ย that subsequently swung into a La Niรฑa, for example, had a tremendous influence on global maize yields. It was responsible for affecting the maize yields on nearly every continent that year.
But when I say ENSO is a control freak, I donโt just mean that it organizes the spatialย patternย ofย globalย crop yields. It can also tie good or bad years together across time.
La Niรฑas bring a friend
One feature of ENSO thatโs particularly relevant to agriculture is that La Niรฑas often come in pairs andย occur back to back, like those terrifying twins fromย The Shining. The avid reader of theย ENSO Blogย may already know this, given that last year was a La Niรฑa year, and here we are again in aย La Niรฑa Watch. And, unfortunately, just like those nightmarish ghoul-girls, more isnโt always better in regions where La Niรฑa tends to cause drought. In areas like theย southern US, the Horn of Africa, and southeast South America, multiple La Niรฑasย mayย mean consecutive years of poor crop yields (4). In these regions, multi-year droughts can deplete water reservoirs used for agriculture and could draw down grain reserves two years in a row. In southeast South America, for example, there is good evidence that multiple La Niรฑas often mean consecutive years of below-expected yields (Anderson et al., 2017). So, these regions may understandably want to prepare for the possibility of a second consecutive year of poor yields given the current La Niรฑa Watch.
Aside from worry, what should we do?
Going forward, the climate science community would do well to strengthen working relationships with the food systems and food security community. And Iโm not just talking about agronomists. We need to be working with those that study pastoralists, aquaculture, and global trade as well (among others). By doing so, we can make good use of the truly remarkable knowledge amassed by the climate science community with respect to the way that ENSO organizes global climate, and, therefore, presents a structured risk to the global food system.
Lead Editor:ย ย Michelle LโHeureux (NOAA CPC)
Footnotes:
(1)ย This can be a problem when the cost of globally traded crops spikes, making food unaffordable for many of the worldโs most food insecure as a result of events happening thousands of miles away. This occurred during the global food price crisis of 2008 and again in 2011.
(2)ย Granted, the relationship between the climate and crop yields is not always straightforward; but the fundamental ways that ENSO affects crop yields is no different from how it affects, say, precipitation. For example,ย wheat yields in Australia are related to those in southeast South America due to the basin-wide atmospheric circulation response to tropical convection forced by ENSO in the South Pacific during southern hemisphere spring, which is the wheat growing season in both regions. Australia is on the western edge of the circulation response, while southeast South America is on the eastern edge, affected by the Rossby Wave response known as the Pacific-South American pattern (a southern hemisphere counterpart to the Pacific-North American pattern thatย Michelle previously discussed; see also Anderson et al., 2018). Likewise, crop yields in southeast South America and North America are related to one another because when ENSO affects convection in the tropical Pacific, it forces Rossby Waves to propagate into the midlatitudes of both hemispheres, which affects precipitation over major wheat and maize growing regions in both North and South America. Although the growing seasons are offset in the Americas, ENSO forces an atmospheric response that affects South America during the peak of the ENSO event (Southern Hemisphere summer), while North American growing seasons are affected by either a developing or decaying ENSO event (Anderson et al., 2017; Anderson et al., 2018)
(3)ย ENSO is estimated to affect crop yields on ~28% of global croplands (Heino et al. 2018). This really highlights how widespread the spatial footprint of ENSO is despite the fact that it is strongest during the winter in the northern hemisphere. When we measure the influence of ENSO on the year-to-year variability of global crop production, it accounts for only about 18%, 7%, and 6% of global year-to-year yield variability for maize, wheat, and soybeans, respectively (Anderson et al., 2019). In individual regions, however, the influence of ENSO on the year-to-year variability of crop yields is much larger. In southeastern Africa, for example, ENSO accounts for over a quarter of all year-to-year variability in maize yields (Anderson et al., 2019).
(4) For those keeping score, the crops grown during Southern Hemisphere summer in each of the aforementioned regions did experience poor growing conditions that reduced expected crop yields during the peak of last yearโs La Niรฑa (2020-21).
References:
Handler, P. and Handler, E., 1983. Climatic anomalies in the tropical Pacific Ocean and corn yields in the United States.ย Science,ย 220(4602), pp.1155-1156.
Cane, M.A., Eshel, G. and Buckland, R.W., 1994. Forecasting Zimbabwean maize yield using eastern equatorial Pacific sea surface temperature.ย Nature,ย 370(6486), pp.204-205.
Mauget, S.A. and Upchurch, D.R., 1999. El Niรฑo and La Niรฑa related climate and agricultural impacts over the Great Plains and Midwest.ย Journal of production agriculture,ย 12(2), pp.203-215.
Podestรก, G.P., Messina, C.D., Grondona, M.O. and Magrin, G.O., 1999. Associations between grain crop yields in central-eastern Argentina and El NiรฑoโSouthern Oscillation.ย Journal of Applied Meteorology and Climatology,ย 38(10), pp.1488-1498.
D’Odorico, P., Carr, J.A., Laio, F., Ridolfi, L. and Vandoni, S., 2014. Feeding humanity through global food trade.ย Earth’s Future,ย 2(9), pp.458-469.
Porkka, M., Kummu, M., Siebert, S. and Varis, O., 2013. From food insufficiency towards trade dependency: a historical analysis of global food availability.ย PloS one,ย 8(12), p.e82714.
Heino, M., Puma, M.J., Ward, P.J., Gerten, D., Heck, V., Siebert, S. and Kummu, M., 2018. Two-thirds of global cropland area impacted by climate oscillations.ย Nature communications,ย 9(1), pp.1-10.
Iizumi, T., Luo, J.J., Challinor, A.J., Sakurai, G., Yokozawa, M., Sakuma, H., Brown, M.E. and Yamagata, T., 2014. Impacts of El Niรฑo Southern Oscillation on the global yields of major crops.ย Nature communications,ย 5(1), pp.1-7.
Anderson, W.B., Seager, R., Baethgen, W., Cane, M. and You, L., 2019. Synchronous crop failures and climate-forced production variability.ย Science advances,ย 5(7), p.eaaw1976.
Anderson, W., Seager, R., Baethgen, W. and Cane, M., 2017. Crop production variability in North and South America forced by life-cycles of the El Niรฑo Southern Oscillation.ย Agricultural and Forest Meteorology,ย 239, pp.151-165.
Anderson, W., Seager, R., Baethgen, W. and Cane, M., 2018. Trans-Pacific ENSO teleconnections pose a correlated risk to agriculture.ย Agricultural and forest meteorology,ย 262, pp.298-309.