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Phoenix, Arizona, probably will be the fifth hottest city in the world today, with temperatures that may reach 114 degrees Fahrenheit. Many other parts of the country have sweltered in 100-degree heat this year, which in many cases has been made worse by high humidity. In cities in the Middle East, India and North Africa, 100-degree-plus temperatures are more likely on any given day. They show, however, how wilting heat can become.

One of the differences, for the time being, is that high pollution is combined in some cities, which makes them even less habitable. This is true in India and Tehran. However, heat itself can cut the level of activity in cities in some parts of the world where temperatures reach above 100. Recently, those include some areas in the United States.

What undermines the ability of people to go about their daily business? One is severe health problems for people susceptible to heat, which can even cause deaths. Another is the cut in productivity as people in some professions either have to limit or cease their activity.

In a report covered by Channel NewsAsia, the author wrote:

According to our climate projections and corresponding impact of heat stress on national labour productivity, Southeast Asia is set to experience the greatest loss in labour capacity due to heat stress compared to other regions worldwide, with a projected 16 per cent decrease by 2045.

It appears that 100-degree-plus days are more frequent in a rising number of U.S. cities. Some of these temperatures and their durations are making parts of America like the hottest places in the world.