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Food System Primer

Food and Climate Change



Concentrations of atmospheric greenhouse gases (GHGs).

Prior to the industrial revolution, atmospheric concentrations of GHGs remained relatively stable for thousands of years. It is extremely likely that human activities, such as burning fossil fuels and raising greater numbers of livestock, are the dominant cause of the recent and dramatic rise in GHG concentrations.1 Globally, livestock production accounts for an estimate 14.5 percent of GHG emissions related to human activities.6

Image adapted from the IPCC, 2007.3

Click images for captions

The environmental challenge we are undergoing, and its human roots, concern and affect us all.

– Pope Francis

The term “weather” refers to how the atmosphere behaves in a specific area over a short period of time, usually hours or days. “Climate” refers to general weather patterns over a broad area for a long period of time. Both weather and climate account for qualities like temperature, precipitation, and humidity.

The global climate is warming at an unprecedented rate.1 An overwhelming body of evidence suggests global temperatures will continue to rise, and that human activities such as fossil fuel combustion, deforestation, and agriculture are the dominant cause.1,2 These activities release greenhouse gas (GHG) emissions, such as carbon dioxide, methane, and nitrous oxide, that trap the sun’s heat and warm the atmosphere—hence the name “greenhouse.” Natural processes also produce GHG emissions; however, these have generally been counterbalanced by the capacity of trees, soil, oceans, and other sinks (storehouses) to sequester (capture and store) emissions.3

Climate change is among the greatest threats of our generation—and of generations to come—to public health, ecosystems, and the economy. The projected impacts of climate change, many of which are already occurring, include: 

  • More frequent and intense hurricanes, floods, heat waves, and other extreme weather events
  • Increased heat-related deaths
  • Food and water shortages
  • Forced migration from rising sea levels and natural disasters
  • Increased damages from flooding and wildfires
  • Spreading insect-borne and water-borne diseases4

Scientists and world leaders have called for immediate and dramatic action to reduce GHG emissions, enhance emissions sinks,2 and prepare for the impacts that are expected to occur.5 The food system is one of the areas where urgent interventions are needed most.

Impacts of climate change on agriculture


Texas corn crops affected by drought.

For most of the world’s farmers, the effects of climate change—including worsened problems of droughts, flooding, cyclones, heat waves, and pests—are expected to reduce the amount of food they can grow. Impacts to agriculture can in turn lead to higher food prices.7

Photo credit: Bob Nichols, USDA, 2013. Creative Commons CC BY 2.0.

Drought Kenya

As a result of climate change, many regions that already suffer from high rates of hunger and food insecurity are predicted to experience the greatest declines in food production.7–9 In drought-stricken regions like Kenya (pictured), many cattle farmers have already lost their animals, their livelihoods, and their sources of food and income. Food prices in the area, meanwhile, have skyrocketed.14  

Photo credit: Brendan Cox, Oxfam International, 2004. Creative Commons CC BY-NC-ND 2.0.

Click images for captions

Agriculture has always been at the mercy of unpredictable weather, but a rapidly changing climate is making agriculture an even more vulnerable enterprise. In some regions, warmer temperatures may increase crop yields. The overall impact of climate change on agriculture, however, is expected to be negative—reducing food supplies and raising food prices.7 Many regions already suffering from high rates of hunger and food insecurity, including parts of sub-Saharan Africa and South Asia, are predicted to experience the greatest declines in food production.7–9 Elevated levels of atmospheric carbon dioxide (CO2) are also expected to lower levels of zinc, iron, and other important nutrients in crops.10

With changes in rainfall patterns, farmers face dual threats from flooding and drought. Both extremes can destroy crops. Flooding washes away fertile topsoil that farmers depend on for productivity, while droughts dry it out, making it more easily blown or washed away. Higher temperatures increase crops’ water needs, making them even more vulnerable during dry periods.7

Certain species of weeds, insects, and other pests benefit from higher temperatures and elevated CO2, increasing their potential to damage crops and creating financial hardship for farmers. Shifting climates also mean that agricultural pests can expand to new areas where farmers hadn’t previously dealt with them.11

With higher temperatures, most of the world’s glaciers have begun to recede—affecting farmers who depend on glacial melt water for irrigation.1,5 Rising sea levels, meanwhile, heighten flood dangers for coastal farms, and increase saltwater intrusion into coastal freshwater aquifers—making those water sources too salty for irrigation.12

Climate change is also expected to impact ecosystems and the services they provide to agriculture, such as pollination and pest control by natural predators. Many wild plant species used in domestic plant breeding, meanwhile, are threatened by extinction.13

Food system contributions to climate change


Red meat (beef, pork, and lamb) and dairy production together account for nearly half of the greenhouse gas emissions associated with the U.S. food supply chain.17,18

Image credit: Brent Kim, Johns Hopkins Center for a Livable Future.


Sources of greenhouse gas (GHG) emissions from livestock production..

The single largest share of livestock-related GHG emissions (39%) is from enteric fermentation, a digestive process unique to ruminant animals (e.g., cattle and goats) that releases methane as a byproduct. Most of the methane is released through burping (“eructation”), not farting. Other major sources include manure (26%), which emits methane and nitrous oxide; producing feed for the animals (24%), and clearing forests for feed crops and pasture (9%).6

Brazil Fires

Slash-and-burn rainforest clearing in Matto Grosso, Brazil.

Over 18 percent of the Brazilian Amazon rainforest has been cleared since 1970,19 primarily for cattle ranching.20,21 The Amazon rainforest is one of the world’s most important sinks (storehouses) of carbon, holding the equivalent of 11 years worth of human-caused carbon dioxide emissions.22 Clearing rainforests releases stored carbon, making Brazil among the highest emitters of greenhouse gas emissions in the world.23

Image credit: Image Science & Analysis Laboratory, NASA Johnson Space Center.

GHG Supply Chain

Greenhouse gas (GHG) emissions by stage of supply chain.

GHG emissions associated with U.S. food supply chains are predominantly from food production (83 percent), with much smaller contributions from transporting food and food ingredients (11 percent) and food retail (5 percent).24 Transporting food from stores to homes, home refrigeration, cooking, and emissions from wasted food were not included in these estimates but are also significant contributors of emissions.25


Cattle feeding operation in Yuma, Arizona.

What people eat generally matters more for climate change than how far food travels. Between farms and plates, most food-related greenhouse gas emissions are from producing food—particularly beef and dairy. Research suggests that if U.S. citizens followed plant-based diets even one day per week, they could cut more GHG emissions than by following entirely local diets.17

Photo credit: Jeff Vanuga, USDA Natural Resources Conservation Service.

Eagle Landfill

Bald eagle atop a Florida landfill.

Food waste represents the single largest component (21 percent) of solid waste in landfills and incinerators.26 When food waste decomposes in the absence of oxygen—as is the case when it is buried in landfills—the microorganisms that break it down release methane, a greenhouse gas with 21 times the global warming potential of carbon dioxide.

Photo credit: Andrea Westmoreland. Creative Commons CC BY-SA 2.0.

Click images for captions

Food system activities, including producing food, transporting it, and storing wasted food in landfills, produce greenhouse gas (GHG) emissions that contribute to climate change. Of these sources, livestock production is the largest, accounting for an estimated 14.5 percent of global GHG emissions from human activities.6 Meat from ruminant animals, such as cattle and goats, are particularly emissions-intensive.15

World leaders have agreed that in order to avoid the most catastrophic climate change scenarios, average global temperature rise must not exceed 2° Celsius above pre-industrial levels. Even if this goal is met, many climate impacts, such as sea level rise, will likely still continue for centuries.4

Imagine a scenario in 2050 where societies have transitioned away from coal and natural gas to wind, solar, and other renewable energy sources. In this scenario, public policy and infrastructure investments have made walking, cycling, and public transit the most accessible and popular forms of transportation. Air travel is used only as a last resort. In what is otherwise a best-case scenario, if global trends in meat and dairy intake continue, our chances of staying below the 2° Celsius threshold will still be extremely slim.16 This is why urgent and dramatic reductions in meat and dairy consumption, alongside reductions in GHG emissions from energy use, transportation, and other sources, are crucial to avoiding catastrophic climate change. The responsibility for eating lower on the food chain falls most heavily on countries like the U.S. with the highest per capita consumption of meat and dairy. Changing diets on an international scale will require more than just educating consumers – national policies will need to shift in ways that support more plant-centric diets.16


The following list of suggested resources is intended as a starting point for further exploration, and is not in any way comprehensive. Some materials may not reflect the views of the Johns Hopkins Center for a Livable Future.

For teachers


Academic journal articles


1. IPCC. Summary for Policymakers. In: Stocker TF, Qin D, Plattner G-K, et al., eds. 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, United Kingdom and New York, NY, USA: Cambridge University Press; 2013.
2. IPCC. Summary for Policymakers. In: Edenhofer O, Pichs-Madruga R, Sokona Y, et al., eds. Climate Change 2014, Mitigation of Climate Change. Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge, United Kingdom and New York, NY, USA: Cambridge University Press; 2014.
3. IPCC. Climate Change 2007: Working Group I: The Physical Science Basis. Cambridge, United Kingdom and New York, NY, USA: Cambridge University Press; 2007.
4. IPCC. Summary for Policymakers. In: Climate Change 2014: Synthesis Report. Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge, United Kingdom and New York, NY, USA: Cambridge University Press; 2014.
5. IPCC. Summary for policymakers. In: Field CB, Barros VR, Dokken DJ, et al., eds. Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part A: Global and Sectoral Aspects. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge, United Kingdom and New York, NY, USA: Cambridge University Press; 2014.
6. Gerber PJ, Steinfeld H, Henderson B, et al. Tackling Climate Change through Livestock – A Global Assessment of Emissions and Mitigation Opportunities. Rome: Food and Agriculture Organization of the United Nations; 2013.
7. Nelson GC, Rosegrant MW, Koo J, Robertson R. Climate Change: Impact on Agriculture and Costs of Adaptation. Washington, D.C.: International Food Policy Research Institute; 2009.
8. Gornall J, Betts R, Burke E, et al. Implications of climate change for agricultural productivity in the early twenty-first century. Philos Trans R Soc B Biol Sci. 2010;365(1554):2973-2989.
9. Schmidhuber J, Tubiello FN. Global food security under climate change. Proc Natl Acad Sci. 2007;104(50).
10. Myers SS, Zanobetti A, Kloog I, et al. Increasing CO2 threatens human nutrition. Nature. 2014;510:139–142.
11. U.S. Global Change Research Program. Global Climate Change Impacts in the United States. Cambridge, New York, Melbourne, Madrid, Cape Town, Singapore, São Paulo, Delhi: Cambridge University Press; 2009.
12. Backlund P, Janetos A, Schimel D. The Effects of Climate Change on Agriculture, Land Resources, Water Resources, and Biodiversity in the United States. 2008.
13. Jarvis A, Upadhyaya H, Gowda C, Aggarwal P, Fujisaka S, Anderson B. Climate Change and Its Effect on Conservation and Use of Plant Genetic Resources for Food and Agriculture and Associated Biodiversity for Food Security. Rome: Food and Agriculture Organization of the United Nations; 2010.
14. Hatcher J. Drought in northern Kenya: “Today you are rich, tomorrow you have nothing.” The Guardian. July 2014.
15. Tilman D, Clark M. Global diets link environmental sustainability and human health. Nature. 2014;515(7528):518-522.
16. Kim B, Neff R, Santo R, Vigorito J. The Importance of Reducing Animal Product Consumption and Wasted Food in Mitigating Catastrophic Climate Change. Johns Hopkins Center for a Livable Future; 2015.
17. Weber CL, Matthews HS. Food-miles and the relative climate impacts of food choices in the United States. Environ Sci Technol. 2008;42(10):3508-13.
18. Engelhaupt E. Do food miles matter? Environ Sci Technol. 2008;42(10):3482.
19. Butler RA. Calculating Deforestation Figures for the Amazon. 2014.
20. Greenpeace. Amazon Cattle Footprint: Mato Grosso: State of Destruction. Sao Paulo, Brazil: Greenpeace Brazil; 2009.
21. Barona E, Ramankutty N, Hyman G, Coomes OT. The role of pasture and soybean in deforestation of the Brazilian Amazon. Environ Res Lett. 2010;5(2):024002.
22. Butler RA. Amazon rainforest locks up 11 years of CO2 emissions. Mongabay.com2. 2007.
23. World Resources Institute. CAIT 2.0. 2014.
24. Weber CL, Matthews HS. Food-miles and the relative climate impacts of food choices in the United States. Environ Sci Technol. 2008;42(10):3508-3513.
25. Garnett T. Cooking up a storm and our changing climate. 2008.
26. U.S. Environmental Protection Agency. Reducing Food Waste for Business. 2014.