Heat stress is Becoming Increasingly Widespread as a Result of Climate Change

Most individuals are experiencing a particularly hot summer. This year, scorching temperatures have plagued Western Europe, the Mid-Atlantic, and the Northeast United States. As people suffer from extreme heat more frequently and for longer, climate change becomes that much harder to ignore.  

Compared to other catastrophes such as hurricanes, floods, and tornadoes, heat is much less tangible. When the body is under stress from overheating and cannot get rid of excess heat, a series of negative health effects called heat stress —including symptoms such as cramps, exhaustion and nausea—may occur. According to the National Weather Service, heat stress kills more Americans each year than any other weather threat. 

A heat index quantifies the effects of temperature and relative humidity on heat stress into a single number expressed as a temperature. The National Weather Service in the United States classifies temperatures exceeding 103°F as "hazardous" due to the likelihood of cramps and exhaustion. A Heat Index of 124°F or more is considered "very hazardous" and can result in heat stroke, a condition with a high mortality rate. What's more, according to the Centers for Disease Control and Prevention (CDC), 702 heat-related deaths occur in the United States each year. 

How will global warming and climate change affect human heat stress? On August 25, a new study published in Communications Earth & Environment quantified the change in exposure to dangerously high temperatures caused by climate change using forecasts of anthropogenic CO2 concentrations. The findings show that climate change caused by these emissions will result in over a billion people who live in tropical and subtropical regions experiencing temperatures that exceed dangerous heat index levels each year by 2100 if major emissions reductions are not implemented. 

According to this research, even if the Paris Climate Agreement goal is met, it would not be enough to prevent dangerous heat levels in the tropics and subtropics. The Paris Climate Agreement, a United Nations-sponsored agreement to help mitigate the consequences of climate change, aims to keep global temperatures below 2 degrees Celsius, above pre-industrial levels. Without aggressive regulation, human activity's carbon dioxide emissions will continue to raise global temperatures in the decades to come. 

To depict the increased heat stress induced by human emissions, this study estimated the average number of days per year when the heat index will surpass "dangerous" and "very dangerous" thresholds. The image below shows that in both past and present climates, the heat index seldom exceeds highly dangerous levels. However, several places, including Sub-Saharan Africa, sections of the Arabian Peninsula, and much of the Indian subcontinent, will have exceeded the extremely dangerous heat index threshold by 2100 (see below).

Source: Projections of extremely dangerous Heat Index values. Note: All panels include red outlines that show areas where the highly hazardous heat index threshold is exceeded more than once per year on average.

Further, this study finds that due to the location, exposure to dangerous heat index values would certainly increase by 50-100% throughout most of the tropics. Most days of the year, residents are likely to face dangerous and extremely dangerous heat indexes. 

Deadly heat waves are predicted to become more common in mid-latitude states, such as Oregon, Northern California, Wyoming, Colorado, Iowa, Ohio, Virginia and North Carolina, on a yearly basis by a heat index increase of between 3–10. The study uses Chicago as an example, which is expected to witness a 16-fold increase in severe heatwaves by 2100. 

What are our options? 

The fact that climate change raises the heat index is indisputable, but whether it is unavoidable depends on what steps are made to address the issue. Countries must adopt strategies to address heat stress high-risk areas—particularly among the elderly, outdoor workers, and lower income communities. A fundamental climate reorientation and popularization of scientific knowledge about the hazards of excessive heat is required.