As places in the American Southwest swelter under a heat wave (with temperatures reaching into the 120 F in Phoenix or mid 50s C), concerns with high heat events and increased mortality due to climate change have gained increased awareness. A new article published in Nature Climate Change (Mora et al. 2017) highlights the increased risk of mortality due to heat in a warming world. Extreme heat events are well known to have a deadly impact on the population: in 1995, some 740 deaths in Chicago were attributed to heat. Likewise, nearly 5,000 deaths were attributed to extreme heat in Paris in 2003. The elderly, along with those in poor health and individuals with lower socio-economic status are at greater risk of dying in such events.
Work by Mora et al. quantified the risk of mortality based on extreme heat events, and found the threshold beyond which temperature and humidity become deadly. The surprising finding is that the threshold is relatively low: with low humidity, the threshold is just 30 C (with average temperatures based on daily highs nightly lows). If the humidity is greater than 50 percent, the threshold falls into the mid-20s C. When temperature, or temperature and humidity exceed these thresholds, the risk for death increases.
Ultimately, the researchers found that approximately 30% of the global population is currently exposed to deadly heat conditions up to 20 days a year. Given climate change, this proportion increases dramatically, with projections suggesting that 74% of the world’s population will be at risk by 2100, if emissions continue to rise. In short, the risk of death due to extreme heat will increase dramatically over the coming decades due to climate change. Even populations living in mid-latitude regions will be at increased risk for death due to heat.
So, given that climate change is happening, what can we do to mitigate the chance of dying during heat waves that are projected to occur more often, longer, and over a wider geographic area? Governments must assist their populations in adapting to high heat conditions, so that people know how to take protective actions such as staying in cooled areas or using cooling centers. Vulnerable populations, such as the elderly, must be monitored. Trees and green spaces can also help with cooling.
Camilo Mora et al. 2017. Global Risk of Deadly Heat. Nature Climate Change, doi:10.1038/nclimate3322