Directions for teachers:

Ask students to read the online Science News article “Humans may not be able to handle as much heat as scientists thought,” which explores the effects of extreme heat on the body and what that means for us as heat waves intensify around the globe, and answer the following questions. A version of the article, “How much heat can we handle?” appears in the August 27, 2022 issue of Science News.

1. What type of extreme weather event was a hallmark of summer 2022?

Heat wave.

2. How can extreme heat impact the body?

Extreme heat can increase aggression and decrease focus, and cause dehydration, cramps, exhaustion, stroke and even death.

3. What are some ways that the body keeps itself cool? How does the environment affect how the body cools itself?

The body cools itself by sweating and increasing heart rate. Increased heart rate boosts blood flow, which carries excess heat to the skin where air can wick the heat away. Bodies in hot, dry environments rely on sweating whereas bodies in warm and wet conditions can’t sweat efficiently due to the moisture in the air, so they rely on the air itself to wick the heat away.  

4. What is the theoretical maximum temperature that humans can endure? What regions of the world are projected to regularly exceed this temperature in the near future?

The theoretical maximum temperature that humans can endure is 35° Celsius. Parts of South Asia and the Middle East could regularly experience temperatures higher than this limit by the middle of the century.

5. What is humankind’s real-world threshold for heat stress, according to recent experiments?

There isn’t a single temperature that fits everyone. But according to tests of 24 young, healthy adults, those in warm and humid conditions were unable to tolerate heat stress at 30° or 31° C. Participants in hot and dry conditions were unable to tolerate heat stress at 25° to 28° C.

6. How do the findings compare with the theoretical threshold? What do the findings suggest about the impacts of heat waves on people?

The findings were lower than the theoretical threshold. And the thresholds for people who work outdoors, children and the elderly are probably even lower. Overall, the findings suggest that the human body’s heat tolerance is lower than scientists realized, which could mean millions of more people will be at risk from deadly heat waves.

7. Why are heat waves at temperatures lower than the thresholds still dangerous? Explain.

Regions that aren’t used to such heat may experience more deaths from heat waves because the people that live there can’t adapt quickly.

8. How are researchers and government officials raising awareness about heat waves?

Researchers have created a severity ranking system and have suggested naming heat waves, similar to how hurricanes are ranked and named. The hope is that ranking and naming heat waves will raise awareness among the public and improve government responses to keep people safe.

9. What is the first named heat wave called? Where and when did the heat wave happen?

In late July, the city of Seville in Spain named a heat wave Zoe.

Analyze this

1. Look at the graph titled “Rising heat.” What type of graph is it?

Bar graph.

2. What does the graph show?

The change in the duration of heat wave season.

3. What is shown on the x- and y-axis? Make sure to include units in your answer.

The y-axis represents the average length of heat wave season in days, and the x-axis represents time in decades.

4. Describe the trend shown by the graph. How has the heat wave season in the United States changed over time?

The bars become taller from left to right. That means that the average length of the heat-wave season has increased over time. In the 1960s, the average heat wave season in the United States lasted about 22 days. By the 2010s, the average heat wave season lasted nearly 70 days.