Guest essay by Eric Worrall

Apparently the models can tease out the difference between armed thugs looting and destroying farms, and the impact of a very small shift in global temperature.

Climate change is affecting crop yields and reducing global food supplies

July 9, 2019 9.22pm AEST
Deepak Ray Senior scientist, University of Minnesota

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To analyze these questions, a team of researchers led by the University of Minnesota’s Institute on the Environment spent four years collecting information on crop productivity from around the world. We focused on the top 10 global crops that provide the bulk of consumable food calories: Maize (corn), rice, wheat, soybeans, oil palm, sugarcane, barley, rapeseed (canola), cassava and sorghum. Roughly 83 percent of consumable food calories come from just these 10 sources. Other than cassava and oil palm, all are important U.S. crops.

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Once we had constructed an empirical model connecting crop yield to weather variations at each location, we could use it to assess how much yields had changed from what we would have expected to see if average weather patterns had not changed. The difference between what we would have predicted, based on the counterfactual weather, and what actually occurred reflects the influence of climate change.

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What’s more, we found that decreases in consumable food calories are already occurring in roughly half of the world’s food insecure countries, which have high rates of undernourishment, child stunting and wasting, and mortality among children under age 5 due to lack of sufficient food. For example, in India annual food calories have declined by 0.8% annually and in Nepal they have fallen by 2.2% annually. 

Reductions are also occurring in southern African countries, including Malawi, Mozambique and Zimbabwe. We even found losses in some rich industrialized nations, such as Australia, France and Germany. 
Rich countries can work their way out of food calorie shortages by importing food. But poorer countries may need help. Short-term strategies could include using our findings to breed or increase cultivation of crops that are resilient to or even benefit from climate change. Farming techniques and agriculture policies can also help small-scale farmers increase crop yields.

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Read more: http://theconversation.com/climate-change-is-affecting-crop-yields-and-reducing-global-food-supplies-118897

The abstract of the study;

Climate change has likely already affected global food production
Deepak K. Ray , Paul C. West, Michael Clark, James S. Gerber, Alexander V. Prishchepov, Snigdhansu Chatterjee

Crop yields are projected to decrease under future climate conditions, and recent research suggests that yields have already been impacted. However, current impacts on a diversity of crops subnationally and implications for food security remains unclear. Here, we constructed linear regression relationships using weather and reported crop data to assess the potential impact of observed climate change on the yields of the top ten global crops–barley, cassava, maize, oil palm, rapeseed, rice, sorghum, soybean, sugarcane and wheat at ~20,000 political units. We find that the impact of global climate change on yields of different crops from climate trends ranged from -13.4% (oil palm) to 3.5% (soybean). Our results show that impacts are mostly negative in Europe, Southern Africa and Australia but generally positive in Latin America. Impacts in Asia and Northern and Central America are mixed. This has likely led to ~1% average reduction (-3.5 X 10¹³ kcal/year) in consumable food calories in these ten crops. In nearly half of food insecure countries, estimated caloric availability decreased. Our results suggest that climate change has already affected global food production.

Published: May 31, 2019
https://doi.org/10.1371/journal.pone.0217148

Read more: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0217148

First, top marks for accessibility, for providing public access to the full study.

The claim about Zimbabwe intrigued me, because Zimbabwe has been suffering problems other than shifting weather patterns.

From the study;

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Of the major sub-Saharan African crops, maize provides the largest percentage of food calories followed by sorghum, cassava and sugarcane. Maize and sugarcane yields decreased by 5.8% and 3.9%, respectively. In contrast, recent climate change caused yields to increase in the more heat- and drought-tolerant sorghum (0.7%) and cassava (1.7%). Maize yield losses are highest in South Africa (-22%), with the highest losses occurring in the provinces of The Free State and North West (Fig 1). Overall in Sub-Saharan Africa maize yields have decreased but cassava yields increased in response to climate changes, though not everywhere. For example cassava yields decreased in the central to southern parts of Madagascar but increased in northeastern Madagascar. Though Eastern Africa in general had reductions in cassava yields, in Tanzania this was true only in its eastern districts and in the western districts cassava yields benefitted from mean climate changes. This apparent heterogeneity in yield response is seen also in Western Africa. For example in the southern districts of Togo maize yields decreased but in the northern districts maize yields benefitted from mean climate change. Consumable food calorie production from these ten crops was reduced nearly 12% (or ~-8% across all food calories) in South Africa. Large decreases in consumable food calories across all ten crops also occurred in Ghana (~-8%) in western Africa, in Zimbabwe (~-10%) in southern Africa, but increased in Tanzania (~2%) in eastern Africa (S4 Table). In some cases, as in Ghana, gains in consumable calories in maize and rice due to climate change was wiped off from losses in cassava consumable calories leading to overall decreases in consumable food calories. Overall in entire sub-Saharan Africa ~1.4% reduction in food calories in these ten crops or ~0.8% reduction across all consumed food calories from these ten crops occurs on average annually due to climate change.

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Read more: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0217148

Not really much additional information.

I’m still not clear how the model accounted for political mismanagement of water resources, which has been rampant in South Africa, Zimbabwe and some green US states like California, soil erosion caused by mismanagement of land in some regions, and long term underinvestment in rural water infrastructure, which is a serious ongoing issue in Australia. Australian farmers are being starved of water resources, to ensure the growing population of city voters receive a steady supply, which could be exacerbating weather related losses.

Having said that I suggest the whole concept of constructing an imaginary “what if” scenario, a hypothetical yield without climate change, a bit suspect, because the conclusion yielded from this exercise is based on the circular assumption that climate change is actually having an impact on weather, that any weather changes are not simply random natural variations, or rainfall changes caused land use changes such as deforestation.