1.74 | Fall 2020 | Graduate

Land, Water, Food, and Climate

SECTION 3 | Reconciling Demand and Supply: Context

Class 8: Climate Change and Agriculture

This class provides a quick survey of the effects of climate change on agriculture as well as the effects of agriculture on climate change. Climate changes of particular importance to crop production include:

  • Increases in mean and extreme temperatures
  • Shifting and extended growing seasons
  • Changes in the distribution and intensity of precipitation
  • More frequent severe weather events.
  • Increases in atmospheric carbon dioxide (can enhance photosynthesis, up to a point)
  • Ecosystem changes driven by temperature and precipitation.

The nature of these changes remains highly uncertain.

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The key question for agriculture and food security is how climate change will impact crop yields. It is possible that some crops, some farmers, and some regions will benefit from climate change while others will suffer adverse consequences. The problem of assessing the impacts of climate change on agriculture requires not only an ability to predict climate but also a better understanding of environmental influences on crop yield. To a first approximation, the net effect of climate change on yield at a given location for a given crop reflects the combination of negative impacts due to increases in temperature (and possibly decreases in rainfall) and positive impacts due to increases in carbon dioxide and a longer growing season (and possibly increases in rainfall).

In the other direction, the most direct impacts of agriculture on climate occur through greenhouse gases emitted by agricultural operations. However, there are also indirect contributions such as the emissions created as by-products during nitrogen fertilizer synthesis or during the clearing of forests for cropland (see S11).

Our readings start with the most recent (2014) “Synthesis Report” from the Intergovernmental Program on Climate Change (IPCC), a United Nations group that regularly compiles information on observations and predictions of climate change. The required portion (SPM1 and SPM2) is a concise summary of findings intended for policy makers but useful to anyone interested in the topic. The additional recommended portion (Topics 1 and 2) provides more detail, including discussions of some of the alternative scenarios considered in the discussion of future climate. This report is useful not just as background but to introduce the vocabulary and perspective of the ‘climate change establishment’. The optional IPCC reading by Stocker et al. (2013) provides more detail on the physical science basis for the findings presented in the Synthesis Report.

The Synthesis Report’s division into sections on past and future climate is representative of research on this topic. Prediction is needed to determine how the climate might change in response to different policies and practices, often formalized in terms of specific scenarios. Analysis of past climate is needed to confirm the accuracy of the models used to make predictions, to obtain better understanding of uncertain physical processes, and to establish context for scenario predictions. Since different models can give significantly different predictions, for example predicting an increase vs. a decrease in average rainfall, it can be difficult to interpret model-based forecasts of climate change. The IPCC reports try to convey the diversity of results obtained from different models and to distinguish predictions that are reasonably certain from those that are more uncertain.

The book chapter by Ruane and Rosenzweig (2019) provides a focused discussion of the connections between climate and agriculture. The prediction section of the paper relies on 29 different climate models and a smaller number of global crop models. The results presented suggest that yields for major grains will generally be adversely impacted by climate change in lower latitude and semi-arid regions and more favorably impacted in colder regions, so long as local soils support increased production.

Morton’s (2007) paper discusses climate change impacts on smallholder and subsistence farmers who are especially vulnerable to reduced yields and increased occurrence of extreme events such as droughts and floods. Most smallholders live in tropical regions where climate-related crop yield reductions and livestock losses are more likely. Climate change adds to a long list of “non-climate stressors” that are already making life difficult for these smallholders. Overall, the Morton paper is useful for emphasizing that climate change will likely have especially devastating impacts on rural low-income populations in developing countries, reflecting the effects of both geography and poverty.

Deutsch et al. (2018) provide a review of possible impacts of climate change on insect pests. This example illustrates one way that climate change could modify ecosystems that are important to agriculture. The analysis depends on a particular model of the effects of temperature changes on the growth and metabolic rates of insects that threaten food crops. The conclusion is that insect-related crop losses could increase substantially (by 10%–25% per degree C of warming) in the temperate areas where most grain is produced. Since the study is based on a relatively simple model and uncertainties are substantial it serves primarily to pose a hypothesis that deserves further investigation.

The readings in this class provide a just glimpse of the many connections between climate and agriculture. However, they clearly convey the view that climate change will be a key consideration in developing a strategy for achieving food security in the 21st century.

Required Readings

Climate Change Summary

  • IPCC, 2014: Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, R.K. Pachauri and L.A. Meyer (eds.)]. IPCC, Geneva, Switzerland, 151 pp. [Required reading: Summary for Policy Makers, Sections SPM1 and SPM2, pp. 1–16; Recommended reading: Topics 1 and 2, pp. 39–74]

Climate and Agriculture

  • A. C. Ruane and C. Rosenzweig. 2019: “Chapter 5: Climate Change Impacts on Agriculture.” In Agriculture & Food Systems to 2050. P. Pingali and R. Serraj, Eds., World Scientific Series in Grand Public Policy Challenges of the 21st Century, vol. 2. World Scientific, pp. 161–191.

Climate and Smallholders

Climate and Pests

Optional Reading

Climate Change Physical Science Basis

  • T. F. Stocker, D. Qin, et al. 2013. “Technical Summary.” In Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

Discussion Points

  • Do you think there is a convincing case that the net effect of climate change on global food production is negative? Is the possible threat to food production as serious a problem as some of the other adverse effects of climate change (e.g. effects on human habitability or on severe weather events)? Please justify your answer.
  • Now consider an expanded version of the first question, which addresses not just food production but food security, by including food accessibility and utilization as well as stability/reliability of supply. Does this change your answer?
  • After reading Morton (2007) what do you think is the best way for smallholders to protect themselves from the adverse effects of climate change? What role do you see for international agencies/governments? 
  • How would you convince a neutral to skeptical ‘policy maker’ to support potentially controversial adaptation and/or mitigation measures to deal with the possible effects of climate change on food security? What measures would you put at the top of your list?

Course Info

As Taught In
Fall 2020
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Lecture Notes
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