U.S. Faces Dramatic Rise in Extreme Heat, Humidity

Extreme heat and the combination of high heat and humidity pose serious risks for human health. According to the National Weather Service, heat is the No.1 weather-related killer in the U.S. -- more than tornados, floods, and hurricanes -- and it is estimated that between 600 and 1,500 heat-related deaths occur in an average summer in the U.S.1,2 Individual heat waves can be even more deadly.

The 1995 heat wave in Chicago is estimated to have led to more than 700 deaths and in excess of 1000 more hospital admissions than normal.

This deadly risk is not likely to go away.  By the end of the century, heat-related deaths are projected to increase by thousands to tens-of-thousands each year in the U.S.  Those most at risk of heat-related health impacts are infants and young children, elderly over 65, those already ill, athletes, and outdoor workers.  But everyone is potentially at risk.

Elevated heat, especially along with high humidity, makes it difficult for the body to cool itself. In addition to increasing the risk of mortality, heat can cause problems throughout the body.  It can range from dehydration, cramps, exhaustion, dizziness, vomiting and heat rash to more serious issues involving kidney failure, heart issues, and exacerbation of respiratory issues. These heat impacts also provide a challenge to the healthcare industry with increased hospitalizations and doctors’ visits and insurance claims.

High heat also impacts other sectors and infrastructure.  Stagnant air often occurs during periods of elevated heat and allows dangerous levels of air pollutants to build up.  High temperatures also directly provide conditions conducive for producing harmful ground-level ozone.  Periods of extreme heat can wither crops and exacerbate drought conditions greatly impacting agriculture.  Blackouts often accompany heat-waves as the need for cooling puts a heavy strain on the power grid.  Heat waves can also lead to harmful algal blooms and promote other bacterial growth in bodies of water and lead to degraded fish habitat, such as for species that require cooler streams and rivers.

The combination of hot temperatures and high humidity create dangerous conditions for humans.  The National Weather Service defines as dangerous any day when the heat index (the combination of heat and humidity, commonly known as the “feels like temperature”) exceeds 104°F.  Under these conditions, sunstroke and heat exhaustion are likely, and physical activity or being outside for long periods is  risky, potentially leading to heat stroke. These dangerous heat days pose the greatest threat to kids and the elderly, and to people who don't have easy access to air conditioning.

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