You are reading Part 8 of 9 in this series.What are Quick Facts?
Climate change is already causing a range of impacts on U.S. food production, including crop losses from flooding, soil erosion, and a decline in winter chill needed for fruit and nut production. While a few states in the Northern Great Plains could see conditions conducive to expanded or alternative crop productivity in the years ahead, yields of most major U.S. crops are expected to decline due to increased heat, changes in water availability, extreme weather events, extended ranges for weeds, diseases, and pest outbreaks, and economically disruptive shifts in growing regions.
Facts for Any Story
Extreme rainfall and flooding, which are becoming more frequent and intense in much of the United States due to climate change, increase soil erosion and nutrient loss, delay planting, impair root growth and function, and reduce field work days.1Walsh et al., (2020) Climate Indicators for Agriculture. USDA Technical Bulletin 1953. View Source2Angel et al., (2018) Midwest. In Impacts, Risks, and Adaptation in the United States: Fourth National Climate Assessment, Volume II. View Source3Gowda et al., (2018) Agriculture and Rural Communities. In Impacts, Risks, and Adaptation in the United States: Fourth National Climate Assessment, Volume II. View Source
Even moderate warming has been shown to reduce yields of some crops, and heat waves—extreme heat events that are increasing in frequency, duration, and geographic extent as a result of human-caused global warming—have even more detrimental effects on many crops including tomatoes, corn, and wheat, especially during sensitive life stages, such as flowering, pollination and ripening.4J.L. Hatfield, J.H. Prueger. (2015) Temperature extremes: Effect on plant growth and development. Weather Clim. Extrem. View Source5Hatfield et al., (2014) Ch. 6: Agriculture. Climate Change Impacts in the United States: The Third National Climate Assessment View Source6Ruiz‐Vera et al., (2015) Canopy warming caused photosynthetic acclimation and reduced seed yield in maize grown at ambient and elevated CO2. View Source7Siebers, M. H. et al., (2017). Simulated heat waves during maize reproductive stages alter reproductive growth but have no lasting effect when applied during vegetative stages. View Source
Fruit and nut trees require adequate winter chill—typically temperatures between 32°F and 45°F—to produce economically viable yields. In California’s Central Valley—an agriculturally rich fruit- and nut-growing region—the drop in winter chill exposure has been accelerating, with a decline of 5% between 1950 and 2000 and an additional 10% between 2000 and 2021.8Luedeling E. et al., (2009) Climatic Changes Lead to Declining Winter Chill for Fruit and Nut Trees in California during 1950–2099. View Source9Baldocchi, D., Wong, S. (2008) Accumulated winter chill is decreasing in the fruit growing regions of California. View Source Continued winter warming is projected to negatively impact such economically and culturally important crops as California walnuts and apricots, Georgia and South Carolina peaches, and Northeastern plums and cherries.5Hatfield et al., (2014) Ch. 6: Agriculture. Climate Change Impacts in the United States: The Third National Climate Assessment. View Source9Baldocchi, D., Wong, S. (2008) Accumulated winter chill is decreasing in the fruit growing regions of California. View Source10Parker, Lauren E.; Abatzoglou, John T. (2019) Warming Winters Reduce Chill Accumulation for Peach Production in the Southeastern United States. View Source
Cold winter temperatures keep many agricultural pests and pathogens in check. Human-caused warming is raising minimum winter temperatures, facilitating higher densities and expanded ranges of invasive weeds such as Kudzu and insect pests such as the corn rootworm.1Walsh et al. 2020 View Source2Angel et al. 2018 View Source11Bebber, D., Ramotowski, M. & Gurr, S. (2013) Crop pests and pathogens move polewards in a warming world. View Source12Ziska LH, McConnell LL. (2015) Climate Change, Carbon Dioxide, and Pest Biology: Monitor, Mitigate, Manage. View Source
In the last decade, Palmer amaranth—one of the most economically damaging and herbicide-resistant weeds (with reported yield losses up to 91% in corn, 79% in soybean, and 65% in cotton)—has expanded its geographic range northward throughout the Midwest. Future climate change is projected to give Palmer amaranth an even greater competitive edge over warm-season crops.13Kistner, E.J. and Hatfield, J.L. (2018), Potential Geographic Distribution of Palmer Amaranth under Current and Future Climates. Agricultural & Environmental Letters. View Source
The use of herbicides and pesticides has increased in an attempt to combat these invasive species, which in turn is reducing profit margins, accelerating pest resistance, and exacerbating environmental and health impacts.1Walsh et al. 2020 View Source5Hatfield et al. 2014 View Source13Kistner and Hatfield 2018 View Source14Larsen, A.E., Noack, F. (2021) Impact of local and landscape complexity on the stability of field-level pest control. View Source
U.S. production regions for most major crops are shifting, which can cause substantial social and economic disruptions in local communities as land values and employment opportunities change.3Gowda et al. 2018 View Source15Cho, S. J. and McCarl, B. A. (2017) Climate change influences on crop mix shifts in the United States. View Source Research shows that climatic changes, particularly in temperature and precipitation, are substantially responsible for the westward movements of prime growing regions for cotton, hay, spring wheat, and corn, the northward movements of winter wheat, soybeans, corn, and hay, and shifts to higher elevations for hay, soybeans, spring wheat, and corn.15Cho and McCarl 2017 View Source
When climate change or extreme weather events worsen economic outcomes or exacerbate other challenges, farmers and ranchers tend to experience more depression, chronic stress, and lower quality of life.16Hanigan, I. et al., (2012) Suicide and drought in Australia. Proceedings of the National Academy of Sciences. View Source17Edwards, B., Gray, M. & Hunter, B. (2015) The Impact of Drought on Mental Health in Rural and Regional Australia. View Source18Hoell, A. et al., (2020) Lessons Learned from the 2017 Flash Drought across the U.S. Northern Great Plains and Canadian Prairies, Bulletin of the American Meteorological Society. View Source
Shifts in growing zones have ecological implications as well, which can exacerbate climate change. For example, the conversion of forest land to agriculture releases significant carbon from soil and vegetation.19Janowiak, M. et al., (2017) Considering Forest and Grassland Carbon in Land Management. View Source
Elevated levels of carbon dioxide (CO2) are associated with reduced nutritional value of important crops. Laboratory experiments under atmospheric CO2 concentrations of 550 ppm—expected in the next 30-80 years without stringent global mitigation efforts—show that protein, iron, and zinc levels decline by 3-17% in many important food crops including wheat, rice, and barley, with serious implications for nutritional deficiencies for people worldwide.20Smith, M.R., Myers, S.S. (2018) Impact of anthropogenic CO2 emissions on global human nutrition View Source21RH Beach, et al., (2019) Combining the effects of increased atmospheric carbon dioxide on protein, iron, and zinc availability and projected climate change on global diets: a modelling study. Lancet Planet Health. View Source Elevated CO2 also decreases forage quality in grasslands of the western Great Plains, which could hamper livestock weight-gain in the largest rangeland ecosystem in North America.22Augustine, D.J., et al., (2018), Elevated CO2 induces substantial and persistent declines in forage quality irrespective of warming in mixed grass prairie. View Source
Increasing temperatures due to global warming affect many of the critical factors for livestock production, such as water availability and animal reproduction and health. Heat stress in livestock, which occurs when an animal’s body heat increases faster than it can shed that heat, causes substantial declines in performance including decreased milk production and reduced reproduction in dairy cows, declines in poultry meat quality (by altering fat deposition and chemical constituents), and diminished shell quality of eggs.23Becker, C. A. et al., (2020). Invited review: Physiological and behavioral effects of heat stress in dairy cows. Journal of Dairy Science. View Source24Polsky L, von Keyserlingk MAG. (2017) Invited review: Effects of heat stress on dairy cattle welfare. View Source25Godde, C. M., et al., (2021). Impacts of climate change on the livestock food supply chain; a review of the evidence. Global Food Security. View Source26Reeves, M. C.; Bagne, Karen E. (2016) Vulnerability of cattle production to climate change on U.S. rangelands. View Source
Agricultural activities in the United States, including growing crops and raising livestock, were responsible for about 10% of total U.S. human-caused greenhouse gas emissions in 2018.27EPA. (2021, April 14). Sources of Greenhouse Gas Emissions. View Source Reducing agricultural emissions will be necessary to meet climate policy targets.28IPCC. (2018) Global Warming of 1.5°C. An IPCC Special Report on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty. View Source
Agricultural emissions of nitrous oxide, a greenhouse gas far more potent than CO2 at trapping heat, primarily arise from fertilizers and livestock manure. Nitrous oxide emissions can be reduced through efficient fertilizer use and better soil and livestock waste management. Emissions of methane (another highly potent heat-trapping gas) can be reduced by dietary supplements for cattle and by not submerging rice fields.29Hong, C., et al., (2021) Global and regional drivers of land-use emissions in 1961–2017 View Source30Mbow, C. et al., (2019) Food Security. In: Climate Change and Land: an IPCC special report on climate change, desertification, land degradation, sustainable land management, food security, and greenhouse gas fluxes in terrestrial ecosystems. View Source31George Hochmuth, G., Mylavarapu, R., & Hanlon, E. (2014). The four Rs of Fertilizer Management. View Source
Carbon sequestration—capturing and storing atmospheric CO2—in soils and plants can play an important role in reducing agricultural emissions, and is enhanced by land management practices such as not tilling the soil, growing cover crops, and rotating areas for livestock grazing.30Mbow et al. 2019 View Source32Paustian, K. et al., (2019). Soil C Sequestration as a Biological Negative Emission Strategy. Frontiers in Climate View Source
Climate change is estimated to have imposed a 10% to 20% penalty on U.S. agricultural productivity gains between 1961 and 2015.33Ortiz-Bobea, A. et al., (2020) “The Historical Impact of Anthropogenic Climate Change on Global Agricultural Productivity.” arXiv: General Economics. View Source
Pitfalls to Avoid
Because carbon dioxide (CO2) is essential to plant growth, it’s easy to jump to the conclusion that more of it must be good for crops. Although moderately increased levels can make some plants grow faster, recent work suggests these gains are smaller than previous lab experiments had estimated, while other crops, including corn, experience no benefit at all.24Long et al. 2006 View Source Additionally, higher CO2 concentrations generally result in crops with less protein and other nutrients.20Smith and Myers 2018 View Source21Beach et al. 2019 View Source22Augustine et al. 2018 View Source Finally, in many cases, CO2 disproportionately favors weeds over crops, causing more problems for agriculture.34Blumenthal, D.M. et al., (2016) Cheatgrass is favored by warming but not CO2 enrichment in a semi-arid grassland. View Source
Many countries are more vulnerable to climate change impacts on agriculture than the United States. The U.S. food system may come under increasing pressure to produce even more to help offset these global stressors, even as climate pressures increase in the United States and other countries.30Mbow et al. 2019 View Source
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