fers) and coastal lands globally is increasing due to greater withdrawal of groundwater and sea-level rise, making these regions less productive or non-productive. Some pests and weeds that lower the productivity of food crops can thrive better in a CO2-enriched atmosphere (Deutsch et al. 2018; Ziska et al. 2019). Increasing extreme weather (e.g., flood and precipitation events), growing season drought, and increasing fire severity can also be a detriment to food production.
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).
Livestock, not just plants, are impacted by climate change. Milk production decreases as dairy cows are exposed to increased heat (reviewed in Whitlock et al. 2017; Summer et al. 2018). Deaths in all animals, including livestock, increase with excessive heat, and animals with dark coats are more sensitive to extreme heat. Heat waves make livestock less fertile (Takahashi 2012). Extreme weather events, such as flash floods and drought, also lead to increased animal mortality.
Vectors—primarily arthropods such as ticks, mosquitoes and fleas—are organisms that transmit diseases from one host to another. Globally, vector-borne diseases include Zika, plague, dengue, malaria, yellow fever, Chagas disease, and Chikungunya, among others. In the US, Rocky Mountain spotted fever, Lyme disease, and anaplasmosis, all carried by ticks, and West Nile virus, transmitted by mosquitoes, are most prominent. Zika, dengue, Chikungunya, and Eastern Equine Encephalitis are also of concern.
Overall, climate change is expected to increase the range of vectors, primarily ticks and mosquitoes in the US, thereby increasing the number of people exposed to the diseases that these arthropods transmit (Beard et al. 2016; Sonenshine 2018). Recent work by Rosenberg et al. (2018) shows that the number of vector-borne diseases tripled in the US between 2004 and 2016, with over 100,000 cases reported in 2016. Whereas the marked increase is unlikely to be fully attributable to climate change given the complexities of vector life cycles, disease prevalence, and human interactions (well discussed by Ogden 2017), neither can the contribution of climate change be discounted. Thus, concern is reasonable.
The interactions between climate, vectors, and pathogens are complex. For example, for certain mosquitoes increased temperatures boost the rate of reproduction and feeding, lengthen the breeding season, and shorten the maturation time for the pathogens they carry (Patz et al. 1996; Epstein et al. 1998; Epstein 2005). However, such complex relationships vary by locale and species. Temperatures that benefit mosquitoes may be detrimental to ticks; flooding may wash away larval stages of mosquitoes; drought may contribute to a decline in tick numbers. Rodent vectors, such as deer mice that carry Hantavirus, demonstrate equally variable relationships (Mordecai et al. 2012, 2017, 2019).
According to the Centers for Disease Control and Prevention (CDC), Lyme disease is the most common vector-borne illness in the US, with approximately 300,000 total cases diagnosed annually (CDCa undated). Lyme disease is most prevalent in the Northeast, but has been spreading westward and northward into the Midwestern states and farther into Canada. The main vector, the deer or blacklegged tick, is not found in arid parts of the West, requiring more moisture to thrive. Although Lyme disease is the most common tick-borne disease in Montana—averaging 10 cases per year—all cases reported through 2018 came from people infected outside of Montana (MTDPHHSb undated).
West Nile virus
West Nile virus, first reported in the United States in 1999, is found in nearly every country and is the most common mosquito-borne illness in the United States, with 2647 cases and 167 deaths reported in 2018 (CDCb undated). West Nile virus is considered the most important cause of viral encephalitis globally (Chancey et al. 2015; Paz 2015), with increased spread projected with clima