Climate change is affecting Montana’s water quantity and quality (Whitlock et al. 2017; MTDEQ 2019), each of which may, in turn, impact human health. For example, spring floods, which are expected to increase because of earlier snowmelt or extreme precipitation events (see Section 2), affect people’s health in a variety of ways. Immediate impacts include injury, hypothermia, death from drowning, exposure to toxic substances and pathogens released by flood waters, and exacerbation of underlying conditions such as cardiovascular or pulmonary disease (due the flood itself or cleaning up afterwards). Later complications include respiratory and skin infections, vector-borne illnesses, and mental health conditions (Du et al. 2010; Ryan et al. 2015; Paterson et al. 2018).
Floods also increase the risk of mold formation in homes (Bell et al. 2017), an environmental stressor that can impact anyone but particularly American Indian/Alaska Native children (Barros et al. 2018). Even in the absence of flooding, elevated rates of gastrointestinal disease have been associated with precipitation events (Carlton et al. 2016; Levy et al. 2016), as well as with dry conditions (Alexander et al. 2013; Friedrich 2013; Fouladkhah et al. 2019), though the latter association is weaker.
Water quality issues resulting from climate change may also come about because of changes to precipitation runoff, land use, and the way agricultural lands are managed (MTDEQ undated). Changes to the timing and amount of runoff can impact stream turbidity and sediment deposition, plus non-point pollution runoff and subsequent increased stream concentrations of undesirable compounds. Late season droughts may result in higher concentrations of pollutants—including fertilizers and pesticides—in warmer waters, potentially leading to decreased levels of dissolved oxygen and/or increased algal blooms.
Harmful algal blooms, often caused by cyanobacteria, are special cause for concern. Cyanobacteria have increased across the US from under 100 incidents in 2013 to over 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, inclu