ver 500 in 2019 (EWG undated), and are becoming increasingly common in Montana (MTDPHHSa undated). Many factors influence harmful algal blooms, including increased nutrients from agricultural runoff or sewage, changes in water circulation, and increased water temperatures (Paerl and Huisman 2009; Moore et al. 2011; Davidson et al. 2014). Based on climate model projections, Chapra et al. (2017) indicate that concentrations of cyanobacteria are likely to increase across the US, primarily due to water temperature increases and increased nutrient inputs. They predict that the mean number of days of harmful algal bloom occurrence, which is about 7 days/year per water body under current conditions, will increase to 16−23 days in 2050 and 18−39 days in 2090.
Harmful algal blooms can harm human health. Depending on the causative organism and type of exposure, maladies include gastrointestinal symptoms, muscle cramps, skin rashes, liver damage, and even death. In addition, harmful algal blooms can impair municipal water supplies, hamper recreational activity, and cause significant economic hardships (e.g., if tourism declines in the affected areas).
Climate change threatens human health through its effects on agriculture. For Montana, the MCA describes that global warming will influence the distribution of weeds, pathogens, and insect pests and introduce new pests (Whitlock et al. 2017). These changes may alter the types and amount of pesticides used, potentially affecting the health of agricultural workers and others.
In addition, food quantity and quality, including nutrition, are directly and indirectly impacted by climate change (Gowda et al. 2018b) (see sidebar). Grains, for example, provide almost half the calories humans eat and wheat is a major crop in Montana. With increasing atmospheric CO2 levels, plants grow larger and store more carbohydrates (sugars), yet they contain less protein, zinc, iron, and other nutrient concentrations (Myers 2014). Reduced nutrient quality leads to a number of health problems, including:
- Inadequate nutrition can permanently affect the physical and mental development of children. In the US, low iron levels are experienced by one of out of every five children for part of their childhood (Irwin and Jeffrey 2001).
- Low iron levels have been associated with decreased cognitive function (Jáuregui-Lobera 2014), reduced work capacity (Haas and Brownlie 2001), decreased quality of life, and reduced life expectancy (Shander et al. 2014).
- Reduced protein decreases muscle mass.
- Undernourished people have greater difficulty fighting infections.
- Severe zinc deficiency can cause diarrhea, weight loss, skin lesions, and decreased immunity (NCHS undated).
Climate Impacts on Food Availability and Nutrition
Food and nutrition concerns resulting from a warming world could outweigh all other human health impacts brought on by climate change (Springmann et al. 2016). Examples include:
- Elevated CO2 levels can reduce the protein and micronutrient concentration in grains, putting larger swaths of the global population at risk for malnutrition and anemia (Medek et al. 2017; Smith and Myers 2018; Uddling et al. 2018).
- Increased temperatures, both modest and extreme, can lower crop yields (Zhao et al. 2017; Vogel et al. 2019), as can drought (Lesk et al. 2016) and extreme weather events (Nelson et al. 2014).
- Increased food prices are an economic result of lower crop yields, making some foods less available to those who may already be undernourished. Increased food prices disproportionately affect lower income people (Lake et al. 2012).
- Montana has seen longer growing seasons, offset by summers becoming hotter and drier. Hence, it is hard to project whether local food production will increase.
Climate change can also lower the overall quantity of food produced, resulting in multiple impacts including to traditional sources for American Indians (Zhao et al. 2017; Gowda et al. 2018b; see Section 4 sidebar: Changes Rippling Through Our Lives and Waters). The salt content of underground water sources (aqui