More Hot Days

2014 was the hottest year on record globally, and the 10 hottest years on record have all occurred since 1998. As greenhouse gases continue to build and warm the planet, we are seeing an increased number of hot days in the U.S.

While the hottest days of the year are usually during meteorological summer, extreme heat can kick in during late spring and last into early fall. The rise in extreme heat during this time of year brings more than just inconvenience and higher cooling bills.

As temperatures rise, so do evaporation rates. This draws more water vapor into the atmosphere, increasing humidity. Higher humidity makes it more difficult for the body to cool itself. As a consequence, heat exhaustion and heat stroke become greater concerns, especially in large cities.

Cities are further made hotter by the urban heat island effect. Concrete, bricks, and pavement absorb heat during the day and release it at night, which is why cities are warmer than rural locations. However, both rural and urban areas have showed warming in the past decades, so urban heat islands are not solely responsible for the observed rise in temperatures.

Extreme heat waves are usually accompanied by huge domes of hot air, building thousands of feet into the atmosphere. These domes are often cut off from the main jet stream flow, meaning the air stays in the same place for several days, creating air stagnation. With so little movement, pollutants get trapped in the atmosphere, worsening the air quality and increasing the struggle for those with respiratory conditions.