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It is hot out there! No doubt the climate is changing dramatically, and the evidence of profound heat waves and their impacts confront us in large and small ways on a regular basis. Record temperatures are reported year after year. 2016 set record high temperatures; then in 2017, despite La Niña’s cooling influence, temperatures nearly reached the 2016 records. 2018 was not much better, clocking in as the 4th hottest year globally with the US experiencing the hottest May in recorded history. Since the start of the 21st century, the annual global temperature record has been broken five times.1
The beginning of 2019 has begun with weather extremes wreaking havoc with a severe “polar vortex” in North America while Australia baked in blistering heat.2 With global warming, extreme heat is becoming the new normal.
Extreme heat makes most of us cranky, more likely to have temper flares and feel agitated or listless. Yet heat waves are not benign uncomfortable periods but have profound health risks with potential for death. Heat waves are now considered the deadliest weather events, exceeding hurricanes, lightning, tornadoes, floods, and earthquakes combined. The death toll in India, a country with extreme poverty, experienced the fifth deadliest heat wave in history in 2015. That heat wave claimed 2500 heat-related deaths. By comparison, in the US where access to air-conditioning is more readily available, the CDC reported that between 1999 and 2010 there were an average of 618 deaths annually due to extreme heat.3
Extreme heat can have significant effects on mental health and behavior. Given the predictable future of extreme heat waves potentially increasing the population exposure 4 to 6 times by mid-century, it is incumbent upon the psychiatric and mental health community to be knowledge- able about the specific impacts on behavior and psychiatric outcomes and to plan for ways to protect our patients and communities.4
Impacts of extreme heat on behavior and psychiatric conditions
Violence. Evidence linking extreme heat and aggression confirms the general understanding expressed in our colloquial language of “hot headed,” “so hot my blood boils.” One standard deviation of temperature increase leads to a 4% increase in interpersonal violence and 14% increase in group violence.5,6 This has significant implications for domestic violence and impacts on women and children. Burke and colleagues6 warn “Because locations throughout the inhabited world are expected to warm 2 to 4 degrees by 2050, amplified rates of human conflict could represent a large and critical impact of anthropogenic climate change.” Increases of 2 to 10 degrees due to “urban heat islands” caused by asphalt and concrete structures and limited green space compared to adjacent suburban and rural communities may be contributors to increased summer violence in inner cities.
Suicide—a form of violence turned on the self—is increased during extreme heat. Research shows an increase in suicide rates of 0.7% in the US and 2.1% in Mexico during periods of 1 degree Celsius increase over average monthly temperatures. Projecting future impacts of climate change and global warming assuming no reduction in green-house gas emissions, it is estimated that by 2050 there may be between 9000 to 40,000 additional suicides in the US and Mexico. These rates are comparable to the effects on suicide incidence due to economic recessions and unemployment and offset gains in suicide prevention programs and gun control policies.7,8
Mood. The same study on suicide in the US and Mexico also analyzed over 600 million social media communications and found an increase in depressive language and suicidal ideation correlated with increased temperatures—indicating a decrease in mental well-being.7 Meyer8 postulates a biological and physiologic mechanism for these behaviors and suggest that serotonin may play a role. This is an important area for further research.
1. Lindsey R, Dahlman L. Climate Change: Global Temperature. Aug 1, 2018. https://www.climate.gov/news-features/understanding-climate/climate-change-global-temperature. Accessed May 8, 2019.
2. Extreme weather: Polar vortex in midwest, record heat in Australia, weird warmth in Alaska. What’s going on? USA Today, January 30, 2019.
3. Center for Disease Control and Prevention. Climate Change: Extreme Heat. https://ephtracking.cdc.gov/showClimateChangeExtremeHeat.action. Accessed May 8, 2019.
4. NCAR UCAR News. Exposure of US Population to Extreme Heat Could Quadruple by Mid-Century. May 18, 2015. https://www2.ucar.edu/atmosnews/news/15524/exposure-us-population-extreme-heat-could-quadruple. Accessed May 8, 2019.
5. Hsiang S, Burke M, Miguel E. Quantifying the influence of climate on human conflict. Science. 2013;13;341:1235367.
6. Burke M, Hsiang SM, Miguel E. Climate and conflict. Ann Rev Econom. 2015; 7:577-817.
7. Burke M, Gonzalez, Baylis P, et al. Higher temperatures increase suicide rates in the United States and Mexico. Nature Climate Change. 2018;8:723-729.
8. Meyer R. Climate change may cause 26,000 more US suicides by 2050. The Atlantic. July 23, 2018. https://www.theatlantic.com/science/archive/2018/07/high-temperatures-cause-suicide-rates-to-increase/565826/. Accessed May 14, 2019.
9. Guillermo-Cedeño J, Williams A, Oulhote Y, et al Reduced cognitive function during a heat wave among residents of non-conditioned buildings: an observational study of young adults in the summer of 2016. Plos Medicine. July 2018.
10. Hancock PA, Vasmatzidiis I. Effects of heat stress on cognitive performance: the current state of knowledge. Int J Hyperthermia. 2003;19:355-372.
11. Obradovich N, Migliorini R, Mednick S, Fowler JH. Nightime temperature and human sleep loss in a changing climate. Science Adv. 2017. https://advances.sciencemag.org/content/3/5/e1601555. Accessed May 14, 2019.
12. Wang X, Lavigne E, Ouellette-Kuntz H, Chen BE. Acute impacts of extreme temperature exposure on emergency room admission related to mental and behavior disorders in Toronto, Canada. J Affect Disord. 2014;155:154-161.
13. Hansen A, Bi P, Nitschke M, et al. The Effect of Heat Waves on Mental Health in a Temperate Australian City. Environ Health Perspect. 2008;116:1369-1375.
14. Bark N. Deaths of psychiatric patients during heat waves. Psychiatr Serv. 1998;8:1088-1090.
15. Bouchama A, Dehbi M, Mohamed G, et al. Prognostic factors in heat wave related deaths: a meta-analysis. Arch Intern Med. 2007;167:2170-2176.
16. Chong TW, Castle DJ. Layer upon layer: thermoregulation in schizophrenia. Schizophr Res. 2004:69:149-157.
17. Martin-Latry K, Goumy MP, Latry P, et al. Psychotropic drugs use and risk of heat-related hospitalization. Eur Psychiatry. 2007;22:335-338.
18. Centers for Disease Control and Prevention. Climate Change and Extreme Heat Events. https://www.cdc.gov/climateandhealth/pubs/ClimateChangeandExtremeHeatEvents.pdf. Accessed May 8, 2019.