Extreme heat causes both direct and indirect impacts on human health and acts as a threat multiplier to the medically vulnerable. The increase in extreme heat due to climate change will exacerbate the medical issues associated with heat illness. More detail can be found in Chapter 14: Human Health. Notably, heat stress is strongly correlated with complications of lung disease, such as asthma and emphysema, as well as dehydration and injurious electrolyte abnormalities. It is estimated that each increase of approximately 1.8°F (1°C) in summer temperature increases the death rate for elders with chronic conditions by 2.8% to 4.0%.140 During heat waves, concrete, blacktop, and the low ventilation capacity of urban “canyons” created by tall buildings can add 7°–12°F to the urban heat load.141 The heat wave of 2011 exemplifies the human health and healthcare system impacts of extreme heat in the Southern Great Plains. The average temperature in Texas from June to August that year was 86.7°F (30.4°C), which broke all previous single-month records and was 5.2°F (2.9°C) higher than the long-term climatological average.11 Studies demonstrated a 3.6% increase in emergency room visits and a 0.6% increase in deaths, with the largest effect on the elderly.142,143 Within the Southern Great Plains, changes in extreme temperatures are projected to result in an additional 1,300 deaths per year under a higher scenario (RCP8.5) by the end of the century. Under a lower scenario (RCP4.5), more than half of these additional deaths could be avoided. Annual losses associated with extreme temperature-related mortality are estimated at $19 billion (2015 dollars) under RCP8.5 in 2090 and $9.4 billion (2015 dollars) under RCP4.5144 (see the Scenario Products section of App. 3 for more on RCPs).
Rising temperatures and precipitation alter the habitats of vectors (mosquitoes, ticks, rodents, and fleas) that transmit a variety of human diseases. In the Southern Great Plains, hantavirus,145 Rocky Mountain spotted fever,146 leptospirosis,147 and West Nile virus148 are all currently endemic and could be impacted by climate change.149,150 A warmer world will create newly hospitable habitats for tropical and subtropical insect vectors and the diseases they carry. Historically disease-free areas have been protected from becoming hazardous by cold environmental temperatures. That is, with extreme low temperatures of winter, insect (in particular, mosquito) populations are decimated. However, as the global average temperature increases, mosquitoes will thrive longer and reproduce more successfully at higher latitudes and altitudes. Tropical diseases, such as dengue virus,151 chikungunya virus, and Zika virus are transmitted by Aedes mosquitoes, which are currently expanding their geographic range in the southern United States.149 In southern Texas, sporadic, locally acquired outbreaks of dengue have been reported.152 In 2005, there were 59 cases of dengue virus in southern Texas that met criteria for dengue hemorrhagic fever,153 indicating that inhabitants were exposed to multiple variations of the virus, a condition necessary for the development of severe manifestations of dengue. In 2014, locally transmitted cases of chikungunya began to be reported in Texas.154 Zika virus has also recently appeared in the region. In 2016, the Centers for Disease Control and Prevention (CDC) issued a travel warning for Cameron County, Texas, after the first case of local, person-to-person transmission of Zika was reported.155 The ecology of vector-borne diseases is complex, and the future risk for proliferation and expansion of the ranges of these diseases is possible under future climate scenarios.156,157 Along the southern Gulf Coast, stronger hurricanes will increase the likelihood of favorable ecologic niches for emerging infectious diseases that infect humans and animals.158
As water evaporates during periods of drought, the remaining water can have higher concentrations of chemicals and solid particles, lower dissolved oxygen levels, and a higher density of germs that cause infectious diseases.128 Drought conditions reduce the number of sources and overall quantity of water available to both human and animal users. Because these users are sharing a reduced supply, germ transmission and outbreaks of infectious disease become more likely. Waterborne diseases that have been linked to drought include amoebiasis, hepatitis A, salmonellosis, schistosomiasis, shigellosis, typhoid and paratyphoid fevers, infection with E. coli, cholera, and leptospirosis.159,160,161,162 Skin infections, such as scabies and impetigo, and eye infections, including conjunctivitis, are also correlated with drought due to a lack of water available for personal hygiene.163
Droughts, floods, and higher temperatures will change the balance of ecosystems, allowing invasive species such as animal pests, plant weeds, and algae blooms to proliferate and harm existing agriculture.164 Such conditions favor fungal species that can overwhelm crops and contaminate animal feedstocks. Additionally, increases in CO2 are changing the nutritional composition of food crops.165 Elevated CO2 levels have been shown to reduce the protein composition of grains, tubers, rice, wheat, and barley.166 Micronutrient contents are also affected by rising CO2 levels, with atmospheric CO2 concentrations of 550 parts per million being associated with reductions in zinc, iron, phosphorus, potassium, calcium, sulfur, magnesium, copper, and manganese across a wide range of crops.167 Additionally, extreme temperatures and aridity pose health risks to outdoor agricultural workers.168 Under a higher scenario (RCP8.5), the impact of temperature extremes at a national level are projected to result in the loss of two billion labor hours, equating to an estimated $160 billion (in 2015 dollars) in lost wages by the end of the century. The Southern Great Plains region is projected to experience higher-than-average impacts, with some communities projected to lose more than 6% in annual labor hours by the end of the century.144
State-level climate adaptation programs169 have been developed throughout the Nation. For health, these include vulnerability and adaptation assessments, comprehensive response plans,170,171 climate-proofing healthcare infrastructure, and implementing integrated surveillance of climate-sensitive infectious diseases. These efforts are outlined in more detail in Chapter 14: Human Health. Incorporating short-term to seasonal forecasts into public health activities can also provide assistance under a warming climate.172 Although there is momentum to adopt adaptation strategies in the wake of Hurricane Harvey,173 and adaptation strategies on a general scale (such as for drought) are in progress,174 large-scale adaptation efforts in the region are lacking175 and regional planners can learn from activities ongoing outside the region (Ch. 14: Human Health).