7

Food Safety, Nutrition, and Distribution

7.1 Introduction

  • Lewis H. Ziska
    U.S. Department of Agriculture
  • Allison R. Crimmins
    U.S. Environmental Protection Agency
  • Allan Auclair
    U.S. Department of Agriculture
  • Stacey DeGrasse
    U.S. Food and Drug Administration
  • Jada F. Garofalo
    Centers for Disease Control and Prevention
  • Ali S. Khan
    University of Nebraska Medical Center
  • Irakli Loladze
    Bryan College of Health Sciences
  • Adalberto A. Pérez de León
    U.S. Department of Agriculture
  • Allan Showler
    U.S. Department of Agriculture
  • Jeanette Thurston
    U.S. Department of Agriculture
  • Isabel Walls
    U.S. Department of Agriculture

A safe and nutritious food supply is a vital component of food security. Food security, in a public health context, can be summarized as permanent access to a sufficient, safe, and nutritious food supply needed to maintain an active and healthy lifestyle.1

The impacts of climate change on food production, prices, and trade for the United States and globally have been widely examined, including in the U.S. Global Change Research Program (USGCRP) report, “Climate Change, Global Food Security, and the U.S. Food System,” in the most recent Intergovernmental Panel on Climate Change report, and elsewhere.1,2,3,4,5,6,7 An overall finding of the USGCRP report was that “climate change is very likely to affect global, regional, and local food security by disrupting food availability, decreasing access to food, and making utilization more difficult.”1

This chapter focuses on some of the less reported aspects of food security, specifically, the impacts of climate change on food safety, nutrition, and distribution in the context of human health in the United States. While ingestion of contaminated seafood is discussed in this chapter, details on the exposure pathways of water-related pathogens (for example, through recreational or drinking water) are discussed in Chapter 6: Water-Related Illness.

Systems and processes related to food safety, nutrition, and production are inextricably linked to their physical and biological environment.5,8 Although production is important, for most developed countries such as the United States, food shortages are uncommon; rather, nutritional quality and food safety are the primary health concerns.5,9 Certain populations, such as the poor, children, and Indigenous populations, may be more vulnerable to climate impacts on food safety, nutrition, and distribution (see also Ch. 9: Populations of Concern).

There are two overarching means by which increasing carbon dioxide (CO2) and climate change alter safety, nutrition, and distribution of food. The first is associated with rising global temperatures and the subsequent changes in weather patterns and extreme climate events.10,11,12 Current and anticipated changes in climate and the physical environment have consequences for contamination, spoilage, and the disruption of food distribution.

The second pathway is through the direct CO2 “fertilization” effect on plant photosynthesis. Higher concentrations of CO2 stimulate carbohydrate production and plant growth, but can lower the levels of protein and essential minerals in a number of widely consumed crops, including wheat, rice, and potatoes, with potentially negative implications for human nutrition.13

 

Figure 7.1: Farm to Table: The Potential Interactions of Rising CO2 and Climate Change on Food Safety and Nutrition

Figure 7.1: Farm to Table: The Potential Interactions of Rising CO<sub>2</sub> and Climate Change on Food Safety and Nutrition
The food system involves a network of interactions with our physical and biological environments as food moves from production to consumption, or from “farm to table.” Rising CO2 and climate change will affect the quality and distribution of food, with subsequent effects on food safety and nutrition.

7.2 Food Safety

Although the United States has one of the safest food supplies in the world,18 food safety remains an important public health issue. In the United States, the Centers for Disease Control and Prevention (CDC) estimate that there are 48 million cases of foodborne illnesses per year, with approximately 3,000 deaths.19 As climate change drives changes in environmental variables such as ambient temperature, precipitation, and weather extremes (particularly flooding and drought), increases in foodborne illnesses are expected.20,21

Most acute illnesses are caused by foodborne viruses (specifically noroviruses), followed by bacterial pathogens (such as Salmonella; see Table 7.1). Of the common foodborne illnesses in the United States, most deaths are caused by Salmonella, followed by the parasite Toxoplasma gondii.22,23,24,25 In addition, climate change impacts on the transport of chemical contaminants or accumulation of pesticides or heavy metals (such as mercury) in food, can also represent significant health threats in the food chain.24,26,27,28,29,30

 

Figure 7.2: Climate Change and Health – Salmonella

Figure 7.2: Climate Change and Health – <em>Salmonella</em>
This conceptual diagram for a Salmonella example illustrates the key pathways by which humans are exposed to health threats from climate drivers, and potential resulting health outcomes (center boxes). These exposure pathways exist within the context of other factors that positively or negatively influence health outcomes (gray side boxes). Key factors that influence vulnerability for individuals are shown in the right box, and include social determinants of health and behavioral choices. Key factors that influence vulnerability at larger scales, such as natural and built environments, governance and management, and institutions, are shown in the left box. All of these influencing factors can affect an individual’s or a community’s vulnerability through changes in exposure, sensitivity , and adaptive capacity and may also be affected by climate change. See Ch. 1: Introduction for more information.

How Climate Affects Food Safety

Climate already influences food safety within an agricultural system—prior to, during, and after the harvest, and during transport, storage, preparation, and consumption. Changes in climate factors, such as temperature, precipitation, and extreme weather are key drivers of pathogen introduction, food contamination, and foodborne disease, as well as changes in the level of exposure to specific contaminants and chemical residues for crops and livestock.31,32,33

The impact of climate on food safety occurs through multiple pathways. Changes in air and water temperatures, weather-related changes, and extreme events can shift the seasonal and geographic occurrence of bacteria, viruses, pests, parasites, fungi, and other chemical contaminants.25,32,33,34,35 For example:

  • Higher temperatures can increase the number of pathogens already present on produce36 and seafood.37,38
  • Bacterial populations can increase during food storage which, depending on time and temperature, can also increase food spoilage rates.39
  • Sea surface temperature is directly related to seafood exposure to pathogens (see Ch. 6: Water-Related Illness).40,41,42
  • Precipitation has been identified as a factor in the contamination of irrigation water and produce,32,33,35,43 which has been linked to foodborne illness outbreaks.44,45
  • Extreme weather events like dust storms or flooding can introduce toxins to crops during development (see Ch. 4: Extreme Events).46
  • Changing environmental conditions and soil properties may result in increases in the incidence of heavy metals in the food supply.47,48,49

Climate Impacts on Pathogen Prevalence

While climate change affects the prevalence of pathogens harmful to human health, the extent of exposure and resulting illness will depend on individual and institutional sensitivity and adaptive capacity, including human behavior and the effectiveness of food safety regulatory, surveillance, monitoring, and communication systems.

Rising Temperature and Humidity

Climate change will influence the fate, transport, transmission, viability, and multiplication rate of pathogens in the food chain. For example, increases in average global temperatures and humidity will lead to changes in the geographic range, seasonal occurrence, and survivability of certain pathogens.9,50,51,52

Ongoing changes in temperature and humidity will not affect all foodborne pathogens equally (Table 7.1). The occurrence of some pathogens, such as Salmonella, Escherichia coli (E. coli), and Campylobacter, could increase with climate change because these pathogens thrive in warm, humid conditions. For example, Salmonella on raw chicken will double in number approximately every hour at 70°F, every 30 minutes at 80°F, and every 22 minutes at 90°F.53,54

Table 7.1: Foodborne Illness and Climate Change

Click on a table row for more information.

Foodborne Hazard Symptoms Estimated Annual Illnesses, Hospital Visits, and Deaths Other Climate Drivers Temperature/ Humidity Relationship
Norovirus Vomiting, non-bloody diarrhea with abdominal pain, nausea, aches, low-grade fever
  • 5,500,000 illnesses
  • 15,000 hospitalizations
  • 150 deaths
 Extreme weather events (such as heavy precipitation and flooding) Pathogens Favoring Colder/Dryer Conditions Pathogens Favoring Warmer/Wetter Conditions
Listeria monocytogene Fever, muscle aches, and, rarely, diarrhea. Intensive infection can lead to miscarriage, stillbirth, premature delivery, or life-threatening infections (meningitis).
  • 1,600 illnesses
  • 1,500 hospitalizations
  • 260 deaths
  
Toxoplasma Minimal to mild illness with fever, serious illness in rare cases. Inflammation of the brain and infection of other organs, birth defects.
  • 87,000 illnesses
  • 4,400 hospitalizations
  • 330 deaths
  
Campylobacter Diarrhea, cramping, abdominal pain, nausea, and vomiting. In serious cases can be life-threatening.
  • 850,000 illnesses
  • 8,500 hospitalizations
  • 76 deaths
 Changes in the timing or length of seasons, precipitation and flooding
Salmonella spp. (non-typhoidal) Diarrhea, fever, and abdominal cramps; in severe cases death.
  • 1,000,000 illnesses
  • 19,000 hospitalizations
  • 380 deaths
 Extreme weather events, changes in the timing or length of seasons
Vibrio vulnificus and parahaemolyticus When ingested: watery diarrhea often with abdominal cramping, nausea, vomiting, fever and chills. Can cause liver disease. When exposed to an open wound: infection of the skin
  • 35,000 illnesses
  • 190 hospitalizations
  • 40 deaths
 Sea surface temperature, extreme weather events
Escherichia coli (E. coli) E. coli usually causes mild diarrhea. More severe pathogenic types, such as enterohemorrhagic E. Coli (EHEC), are associated with hemolytic uremic syndrome (a toxin causing destruction of red blood cells, leading to kidney failure).
  • 200,000 illnesses
  • 2,400 hospitalizations
  • 20 deaths
 Extreme weather events, changes in the timing or length of seasons

Estimated annual number of foodborne illnesses and deaths in the United States. (Adapted from Scallan et al. 2011; Akil et al. 2014; Kim et al. 2015; Lal et al. 2012)22,50,51,112

There is a summertime peak in the incidence of illnesses associated with these specific pathogens (see Figure 7.3).20,50,55,56 This peak may be related not only to warmer temperatures favoring pathogen growth but also to an increase in outdoor activities, such as barbecues and picnics. Risk for foodborne illness is higher when food is prepared outdoors where the safety controls that a kitchen provides—thermostat-controlled cooking, refrigeration, and washing facilities—are usually not available.5,20,21,50,57,58

 

Figure 7.3: Seasonality of Human Illnesses Associated With Foodborne Pathogens

Figure 7.3: Seasonality of Human Illnesses Associated With Foodborne Pathogens
A review of the published literature from 1960 to 2010 indicates a summertime peak in the incidence of illnesses associated with infection from a) Campylobacter, b) Salmonella, and c) Escherichia coli (E. coli). For these three pathogens, the monthly seasonality index shown here on the y-axis indicates the global disease incidence above or below the yearly average, which is denoted as 100. For example, a value of 145 for the month of July for Salmonellosis would mean that the proportion of cases for that month was 45% higher than the 12 month average. Unlike these three pathogens, incidence of norovirus, which can be attained through food, has a wintertime peak. The y-axis of the norovirus incidence graph (d) uses a different metric than (a–c): the monthly proportion of the annual sum of norovirus cases in the northern hemisphere between 1997 and 2011. For example, a value of 0.12 for March would indicate that 12% of the annual cases occurred during that month). Solid line represents the average; confidence intervals (dashed lines) are plus and minus one standard deviation. (Figure sources: a, b, and c: adapted from Lal et al. 2012; d: adapted from Ahmed et al. 2013)51,113

Norovirus, the most common cause of stomach flu, can be transmitted by consumption of contaminated food. Although norovirus generally has a winter seasonal peak (see Figure 7.3), changing climate parameters, particularly temperature and rainfall, may influence its incidence and spread. Overall, localized climate impacts could improve health outcomes (fewer cases during warmer winters) or worsen them (elevated transmission during floods), such that projected trends in overall health outcomes for norovirus remain unclear.50,59

Rising ocean temperatures can increase the risk of pathogen exposure from ingestion of contaminated seafood. For example, significantly warmer coastal waters in Alaska from 1997 to 2004 were associated with an outbreak in 2004 of Vibrio parahaemolyticus, a bacterium that causes gastrointestinal illnesses when contaminated seafood is ingested.60 Vibrio parahaemolyticus is one of the leading causes of seafood-related gastroenteritis in the United States and is associated with the consumption of raw oysters harvested from warm-water estuaries.61 Similarly, the emergence of a related bacterium, Vibrio vulnificus, may also be associated with high water temperatures.42 While increasing average water temperatures were implicated in a 2004 outbreak,60 ambient air temperature also affects pathogen levels of multiple species of Vibrio in shellfish.37,38 For example, Vibrio vulnificus may increase 10- to 100-fold when oysters are stored at ambient temperatures for ten hours before refrigeration.62 Increases in ambient ocean water and air temperatures would accelerate Vibrio growth in shellfish, potentially necessitating changes in post-harvest controls to minimize the increased risk of exposure. (For more information on Vibrio and other water-related pathogens, including contamination of recreational and drinking water, see Ch. 6: Water-Related Illness).

Finally, climate change is projected to result in warmer winters, earlier springs, and an increase in the overall growing season in many regions.63,64 While there are potential food production benefits from such changes, warmer and longer growing seasons could also alter the timing and occurrence of pathogen transmissions in food and the chance of human exposure.65,66,67

Extreme Events

In addition to the effects of increasing average temperature and humidity on pathogen survival and growth, increases in temperature and precipitation extremes can contribute to changes in pathogen transmission, multiplication, and survivability. More frequent and severe heavy rainfall events can increase infection risk from most pathogens, particularly when it leads to flooding.68 Flooding, and other weather extremes, can increase the incidence and levels of pathogens in food production, harvesting, and processing environments. Groundwater and surface water used for irrigation, harvesting, and washing can be contaminated with runoff or flood waters that carry partially or untreated sewage, manure, or other wastes containing foodborne contaminants.57,69,70,71,72,73 The level of Salmonella in water is elevated during times of monthly maximum precipitation in the summer and fall months;58,74 consequently the likelihood of Salmonella in water may increase in regions experiencing increased total or heavy precipitation events.

Water is also an important factor in food processing. Climate and weather extremes, such as flooding or drought, can reduce water quality and increase the risk of pathogen transfer during the handling and storage of food following harvest.9

The direct effect of drought on food safety is less clear. Dry conditions can pose a risk for pathogen transmission due to reduced water quality, increased risk of runoff when rains do occur, and increased pathogen concentration in reduced water supplies if such water is used for irrigation, food processing, or livestock management.31,33,57,75 Increasing drought generally leads to an elevated risk of exposure to pathogens such as norovirus and Cryptosporidium .68 However, drought and extreme heat events could also decrease the survivability of certain foodborne pathogens, affecting establishment and transmission, and thus reducing human exposure.68,76

Mycotoxins and Phycotoxins

Mycotoxins are toxic chemicals produced by molds that grow on crops prior to harvest and during storage. Prior to harvest, increasing temperatures and drought can stress plants, making them more susceptible to mold growth.77 Warm and moist conditions favor mold growth directly and affect the biology of insect vectors that transmit molds to crops. Post-harvest contamination is also affected by environmental parameters, including extreme temperatures and moisture. If crops are not dried and stored at low humidity, mold growth and mycotoxin production can increase to very high levels.78,79

Phycotoxins are toxic chemicals produced by certain harmful freshwater and marine algae that may affect the safety of drinking water and shellfish or other seafood. For example, the alga responsible for producing ciguatoxin (the toxin that causes the illness known as ciguatera fish poisoning) thrives in warm water (see also Ch. 6: Water-Related Illness). Projected increases in sea surface temperatures may expand the endemic range of ciguatoxin-producing algae and increase ciguatera fish poisoning incidence following ingestion.80 Predicted increases in sea surface temperature of 4.5° to 6.3°F (2.5° to 3.5°C) could yield increases in ciguatera fish poisoning cases of 200% to 400%.81

Once introduced into the food chain, these poisonous toxins can result in adverse health outcomes, with both acute and chronic effects. Current regulatory laws and management strategies safeguard the food supply from mycotoxins and phycotoxins; however, increases in frequency and range of their prevalence may increase the vulnerability of the food safety system.

Climate Impacts on Chemical Contaminants

Climate change will affect human exposure to metals, pesticides, pesticide residues, and other chemical contaminants. However, resulting incidence of illness will depend on the genetic predisposition of the person exposed, type of contaminant, and extent of exposure over time.82

Metals and Other Chemical Contaminants

There are a number of environmental contaminants, such as polychlorinated biphenyls, persistent organic pollutants, dioxins, pesticides, and heavy metals, which pose a human health risk when they enter the food chain. Extreme events may facilitate the entry of such contaminants into the food chain, particularly during heavy precipitation and flooding.47,48,49 For example, chemical contaminants in floodwater following Hurricane Katrina included spilled oil, pesticides, heavy metals, and hazardous waste.49,83

Methylmercury is a form of mercury that can be absorbed into the bodies of animals, including humans, where it can have adverse neurological effects. Elevated water temperatures may lead to higher concentrations of methylmercury in fish and mammals.84,85 This is related to an increase in metabolic rates and increased mercury uptake at higher water temperatures.30,86,87 Human exposure to dietary mercury is influenced by the amount of mercury ingested, which can vary with the species, age, and size of the fish. If future fish consumption patterns are unaltered, increasing ocean temperature would likely increase mercury exposure in human diets. Methylmercury exposure can affect the development of children, particularly if exposed in utero.88

Pesticides

Helicopter crop dusting

Crop dusting of a corn field in Iowa.

© Lucas Payne/AgStock Images/Corbis

Climate change is likely to exhibit a wide range of effects on the biology of plant and livestock pests (weeds, insects, and microbes). Rising minimum winter temperatures and longer growing seasons are very likely to alter pest distribution and populations.89,90,91 In addition, rising average temperature and CO2 concentration are also likely to increase the range and distribution of pests, their impact, and the vulnerability of host plants and animals.3,92,93

Pesticides are chemicals generally regulated for use in agriculture to protect plants and animals from pests; chemical management is the primary means for agricultural pest control in the United States and most developed countries. Because climate and CO2 will intensify pest distribution and populations,94,95 increases in pesticide use are expected.96,97 In addition, the efficacy of chemical management may be reduced in the context of climate change. This decline in efficacy can reflect CO2-induced increases in the herbicide tolerance of certain weeds or climate-induced shifts in invasive weed, insect, and plant pathogen populations96,98,99,100,101,102,103,104 as well as climate-induced changes that enhance pesticide degradation or affect coverage.104,105

Increased pest pressures and reductions in the efficacy of pesticides are likely to lead to increased pesticide use, contamination in the field, and exposure within the food chain.106 Increased exposure to pesticides could have implications for human health.5,31,46 However, the extent of pesticide use and potential exposure may also reflect climate change induced choices for crop selection and land use.

Pesticide Residues

Climate change, especially increases in temperature, may be important in altering the transmission of vector-borne diseases in livestock by influencing the life cycle, range, and reproductive success of disease vectors.8,67 Potential changes in veterinary practices, including an increase in the use of parasiticides and other animal health treatments, are likely to be adopted to maintain livestock health in response to climate-induced changes in pests, parasites, and microbes.5,25,106 This could increase the risk of pesticides entering the food chain or lead to evolution of pesticide resistance, with subsequent implications for the safety, distribution, and consumption of livestock and aquaculture products.107,108,109

Climate change may affect aquatic animal health through temperature-driven increases in disease.110 The occurrence of increased infections in aquaculture with rising temperature has been observed for some diseases (such as Ichthyophthirius multifiliis and Flavobacterium columnare)111 and is likely to result in greater use of aquaculture drugs.78

7.3 Nutrition

While sufficient quantity of food is an obvious requirement for food security, food quality is essential to fulfill basic nutritional needs. Globally, chronic dietary deficiencies of micronutrients such as vitamin A, iron, iodine, and zinc contribute to “hidden hunger,” in which the consequences of the micronutrient insufficiency may not be immediately visible or easily observed. This type of micronutrient deficiency constitutes one of the world’s leading health risk factors and adversely affects metabolism, the immune system, cognitive development and maturation—particularly in children. In addition, micronutrient deficiency can exacerbate the effects of diseases and can be a factor in prevalence of obesity.119,120,121,122,123,124

In developed countries with abundant food supplies, like the United States, the health burden of malnutrition may not be intuitive and is often underappreciated. In the United States, although a number of foods are supplemented with nutrients, it is estimated that the diets of 38% and 45% of the population fall below the estimated average requirements for calcium and magnesium, respectively.125 Approximately 12% of the population is at risk for zinc deficiency, including perhaps as much as 40% of the elderly.126 In addition, nutritional deficiencies of magnesium, iron, selenium, and other essential micronutrients can occur in overweight and obese individuals, whose diets might reflect excessive intake of calories and refined carbohydrates but insufficient intake of vitamins and essential minerals.122,127,128,129

How Rising CO2 Affects Nutrition

 

Figure 7.4: Effects of Carbon Dioxide on Protein and Minerals

Figure 7.4: Effects of Carbon Dioxide on Protein and Minerals

VIEW
Direct effect of rising atmospheric carbon dioxide ( CO2 ) on the concentrations of protein and minerals in crops. The top figure shows that the rise in CO2 concentration from 293 ppm (at the beginning of the last century) to 385 ppm (global average in 2008) to 715 ppm (projected to occur by 2100 under the RCP8.5 and RCP6.0 pathways),149 progressively lowers protein concentrations in wheat flour (the average of four varieties of spring wheat). The lower figure—the average effect on 125 plant species and cultivars—shows that a doubling of CO2 concentration from preindustrial levels diminishes the concentration of essential minerals in wild and crop plants, including ionome (all the inorganic ions present in an organism) levels, and also lowers protein concentrations in barley, rice, wheat and potato. (Figure source: Experimental data from Ziska et al. 2004 (top figure), Taub et al. 2008, and Loladze 2014 (bottom figure)).13,132,137

Though rising CO2 stimulates plant growth and carbohydrate production, it reduces the nutritional value (protein and minerals) of most food crops (Figure 7.4).13,130,131,132,133,134,135,136 This direct effect of rising CO2 on the nutritional value of crops represents a potential threat to human health.13,136,137,138,139

Protein

As CO2 increases, plants need less protein for photosynthesis, resulting in an overall decline in protein concentration in plant tissues.137,138 This trend for declining protein levels is evident for wheat flour derived from multiple wheat varieties when grown under laboratory conditions simulating the observed increase in global atmospheric CO2 concentration since 1900.132 When grown at the CO2 levels projected for 2100 (540–958 ppm), major food crops, such as barley, wheat, rice, and potato, exhibit 6% to 15% lower protein concentrations relative to ambient levels (315–400 ppm).13,137,138 In contrast, protein content is not anticipated to decline significantly for corn or sorghum.138

While protein is an essential aspect of human dietary needs, the projected human health impacts of a diet including plants with reduced protein concentration from increasing CO2 are not well understood and may not be of considerable threat in the United States, where dietary protein deficiencies are uncommon.

Micronutrients

The ongoing increase in atmospheric CO2 is also very likely to deplete other elements essential to human health (such as calcium, copper, iron, magnesium, and zinc) by 5% to 10% in most plants.13 The projected decline in mineral concentrations in crops has been attributed to at least two distinct effects of elevated CO2 on plant biology. First, rising CO2 increases carbohydrate accumulation in plant tissues, which can, in turn, dilute the content of other nutrients, including minerals. Second, high CO2 concentrations reduce plant demands for water, resulting in fewer nutrients being drawn into plant roots.136,140,141

The ongoing increase in CO2 concentrations reduces the amount of essential minerals per calorie in most crops, thus reducing nutrient density. Such a reduction in crop quality may aggravate existing nutritional deficiencies, particularly for populations with pre-existing health conditions (see Ch. 9: Populations of Concern).

Carbohydrate-to-Protein Ratio

Elevated CO2 tends to increase the concentrations of carbohydrates (starch and sugars) and reduce the concentrations of protein.137 The overall effect is a significant increase in the ratio of carbohydrates to protein in plants exposed to increasing CO2.13 There is growing evidence that a dietary increase in this ratio can adversely affect human metabolism142 and body composition.143

7.4 Distribution and Access

A reliable and resilient food distribution system is essential for access to a safe and nutritious food supply. Access to food is characterized by transportation and availability, which are defined by infrastructure, trade management, storage requirements, government regulation, and other socioeconomic factors.150

The shift in recent decades to a more global food market has resulted in a greater dependency on food transport and distribution, particularly for growing urban populations. Consequently, any climate-related disturbance to food distribution and transport may have significant impacts not only on safety and quality but also on food access. The effects of climate change on each of these interfaces will differ based on geographic, social, and economic factors.4 Ultimately, the outcome of climate-related disruptions and damages to the food transportation system will be strongly influenced by the resilience of the system, as well as the adaptive capacity of individuals, populations, and institutions.

How Extreme Events Affect Food Distribution and Access

Projected increases in the frequency or severity of some extreme events will interrupt food delivery, particularly for vulnerable transport routes.10,12,151,152 The degree of disruption is related to three factors: a) popularity of the transport pathway, b) availability of alternate routes, and c) timing or seasonality of the extreme event.153 As an example, the food transportation system in the United States frequently moves large volumes of grain by water. In the case of an extreme weather event affecting a waterway, there are few, if any, alternate pathways for transport.154 This presents an especially relevant risk to food access if an extreme event, like flooding or drought, coincides with times of agricultural distribution, such as the fall harvest.

Immediately following an extreme event, food supply and safety can be compromised.154,155,156 Hurricanes or other storms can disrupt food distribution infrastructure, damage food supplies,7 and limit access to safe and nutritious food, even in areas not directly affected by such events (see also Ch. 4: Extreme Events).157 For example, the Gulf Coast transportation network is vulnerable to storm surges of 23 feet.158 Following Hurricane Katrina in 2005, where storm surges of 25 to 28 feet were recorded along parts of the Gulf Coast, grain transportation by rail or barge was severely slowed due to physical damage to infrastructure and the displacement of employees.155,159 Barriers to food transport may also affect food markets, reaching consumers in the form of increased food costs.160

The risk for food spoilage and contamination in storage facilities, supermarkets, and homes is likely to increase due to the impacts of extreme weather events, particularly those that result in power outages, which may expose food to ambient temperatures inadequate for safe storage.156 Storm-related power grid disruptions have steadily increased since 2000.161 Between 2002 and 2012, extreme weather caused 58% of power outage events, 87% of which affected 50,000 or more customers.161 Power outages are often linked to an increase in illness. For example, in August of 2003, a sudden power outage affected over 60 million people in the northeastern United States and Canada. New York City’s Department of Health and Mental Hygiene detected a statistically significant citywide increase in diarrheal illness resulting from consumption of spoiled foods due to lost refrigeration capabilities.162

7.5 Populations of Concern

Climate change, combined with other social, economic, and political conditions, may increase the vulnerability of many different populations to food insecurity or food-related illness. However, not all populations are equally vulnerable.7,64 Infants and young children, pregnant women, the elderly, low-income populations, agricultural workers, and those with weakened immune systems or who have underlying medical conditions are more susceptible to the effects of climate change on food safety, nutrition, and access.

Children may be especially vulnerable because they eat more food by body weight than adults, and do so during important stages of physical and mental growth and development. Children are also more susceptible to severe infection or complications from E. coli infections, such as hemolytic uremic syndrome.168,169,170 Agricultural field workers, especially pesticide applicators, may experience increased exposure as pesticide applications increase with rising pest loads, which could also lead to higher pesticide levels in the children of these field workers.171,172 People living in low-income urban areas, those with limited access to supermarkets,173,174 and the elderly may have difficulty accessing safe and nutritious food after disruptions associated with extreme weather events. Climate change will also affect U.S. Indigenous peoples’ access to both wild and cultivated traditional foods associated with their nutrition, cultural practices, local economies, and community health 175 (see also Ch. 6 Water-Related Illness and Ch. 9: Populations of Concern). All of the health impacts described in this chapter can have significant consequences on mental health and well-being (see Ch. 8 Mental Health).

7.6 Emerging Issues

Climate and food allergies. Food allergies in the United States currently affect between 1% and 9% of the population,176 but have increased significantly among children under age 18 since 1997.177 Rising CO2 levels can reduce protein content and alter protein composition in certain plants, which has the potential to alter allergenic sensitivity. For example, rising CO2 has been shown to increase the concentration of the Amb a 1 protein—the allergenic protein most associated with ragweed pollen.178 However, at present, the question of how rising levels of CO2 and climate change affect allergenic properties of food is uncertain and requires more research.179

Heavy metals. Arsenic and other heavy metals occur naturally in some groundwater sources.180 Climate change can exacerbate drought and competition for water, resulting in the use of poorer-quality water sources.181,182 Because climate and rising CO2 levels can also influence the extent of water loss through the crop canopy, poorer water quality could lead to changes in the concentrations of arsenic and potentially other heavy metals (like cadmium and selenium) in plant tissues. Additional information is needed to determine how rising levels of CO2 and climate change affect heavy metal accumulation in food and the consequences for human exposure.

Zoonosis and livestock. Zoonotic diseases, which are spread from animals to humans, can be transmitted through direct contact with an infected animal or through the consumption of contaminated food or water. Climate change could potentially increase the rate of zoonoses, through environmental change that alters the biology or evolutionary rate of disease vectors or the health of animal hosts. The impact of rising levels of CO2 and climate change on the transmission of disease through zoonosis remains a fundamental issue of potential global consequence.

Foodborne pathogen contamination of fresh produce by insect vectors. Climate change will alter the range and distribution of insects and other microorganisms that can transmit bacterial pathogens such as Salmonella to fresh produce.183,184,185 Additional information is needed regarding the role of climate change on the transmission to and development of food pathogens through insect vectors.

7.7 Research Needs

In addition to the emerging issues identified above, the authors highlight the following potential areas for additional scientific and research activity on food safety, nutrition and distribution, based on their review of the literature. Understanding climate change impacts in the context of the current food safety infrastructure will be improved by enhanced surveillance of foodborne diseases and contaminant levels, improved understanding of CO2 impacts on nutritional quality of food, and more accurate models of the impacts of extreme events on food access and delivery.

Future assessments can benefit from research activities that:

  • synthesize and assess efforts to identify and respond to current and projected food safety concerns and their impacts on human health within the existing and future food safety infrastructure;
  • develop, test, and expand integrated assessment models to enhance understanding of climate and weather variability, particularly extreme events, and the role of human responses, including changes in farming technology and management, on health risks within the food chain; and
  • examine the impacts of rising CO2 and climate change on human and livestock nutritional needs, as well as the impacts of changing nutritional sources on disease vulnerability.186

References

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Likelihood

Very Likely
≥9 in 10		 Likely
≥2 in 3		 As Likely as Not
≈ 1 in 2		 Unlikely
≤ 1 in 3		 Very Unikely
≤1 in 10

Confidence Level

Very High Strong evidence (established theory, multiple sources, consistent results, well documented and accepted methods, etc.), high consensus
High Moderate evidence (several sources, some consistency, methods vary and/or documentation limited, etc.), medium consensus
Medium Suggestive evidence (a few sources, limited consistency, models incomplete, methods emerging, etc.), competing schools of thought
Low Inconclusive evidence (limited sources, extrapolations, inconsistent findings, poor documentation and/or methods not tested, etc.), disagreement or lack of opinions among experts
 

Documenting Uncertainty: This assessment relies on two metrics to communicate the degree of certainty in Key Findings. See Appendix 4: Documenting Uncertainty for more on assessments of likelihood and confidence.

Key Finding 1: Increased Risk of Foodborne Illness

Climate change, including rising temperatures and changes in weather extremes, is expected to increase the exposure of food to certain pathogens and toxins [Likely, High Confidence]. This will increase the risk of negative health impacts [Likely, Medium Confidence], but actual incidence of foodborne illness will depend on the efficacy of practices that safeguard food in the United States [High Confidence].

Key Finding 2: Chemical Contaminants in the Food Chain

Climate change will increase human exposure to chemical contaminants in food through several pathways [Likely, Medium Confidence]. Elevated sea surface temperatures will lead to greater accumulation of mercury in seafood [Likely, Medium Confidence], while increases in extreme weather events will introduce contaminants into the food chain [Likely, Medium Confidence]. Rising carbon dioxide concentrations and climate change will alter incidence and distribution of pests, parasites, and microbes [Very Likely, High Confidence], leading to increases in the use of pesticides and veterinary drugs [Likely, Medium Confidence].

Key Finding 3: Rising Carbon Dioxide Lowers Nutritional Value of Food

The nutritional value of agriculturally important food crops, such as wheat and rice, will decrease as rising levels of atmospheric carbon dioxide continue to reduce the concentrations of protein and essential minerals in most plant species [Very Likely, High Confidence].

Key Finding 4: Extreme Weather Limits Access to Safe Foods

Increases in the frequency or intensity of some extreme weather events associated with climate change will increase disruptions of food distribution by damaging existing infrastructure or slowing food shipments [Likely, High Confidence]. These impediments lead to increased risk for food damage, spoilage, or contamination, which will limit availability of and access to safe and nutritious food depending on the extent of disruption and the resilience of food distribution infrastructure [Medium Confidence].