What caused the recent heat waves in the US?

Extreme heat also increases wildfire risk. The Vision Fire, a 350-acre fire
It controlled 35% of California’s Sequoia National Forest. Graphic: https: //tmsnrt.rs/3T9z9BB

Here are some of the factors that drive heat waves, according to scientists.

Human-caused climate change

Climate change caused by the burning of fossil fuels is a global phenomenon that certainly plays a role in what America is experiencing, scientists say.

“Climate change is making extreme and unprecedented heat events more intense and common around the world,” said Daniel Swain, a climate scientist at the University of California, Los Angeles.

“Heat waves are probably the most underrated potential disasters because they usually kill a lot of people. And we don’t hear about them because they don’t die dramatically, frankly. In the street,” Swain said.

Jennifer Francis, senior scientist at the Woodwell Climate Research Center, said the world is seeing climate change alter wind patterns and weather systems in ways that make heat waves more intense, persistent and widespread.

Alex Ruan, a researcher at NASA’s Goddard Institute for Space Studies, said that as the world warms, it takes less of a natural anomaly to cause extreme heat events.

“The closer we get to those limits, the more likely you are to have more than one heat wave at a time. We’re seeing that right now in the United States.”

Arctic warming and jet stream migration

The Arctic is warming three to four times faster than Earth as a whole, meaning there is less and less difference between temperatures in the north and temperatures near the equator.

This leads to fluctuations in the North Atlantic jet stream, which can lead to extreme weather events such as heat waves and floods, said Francis of the Woodwell Climate Research Center.

Heat domain

Warmer oceans contribute to heat domes, which trap heat over large geographic areas.

The main cause of heat domes is the sharp change in sea temperature from west to east, which occurs in the tropical Pacific during the previous winter.

“When the current moves warm air eastward, the jet stream moves northward, trapping the air and moving it toward land, where it sinks, causing heat waves,” the U.S. National Oceanic and Atmospheric Administration said in a statement.

El Nino and La Nina

Every few years, climate patterns known as El Niño, commonly known as La Niña, occur. El Niño brings warm water from the equatorial Pacific to the west coast of North America, and La Niña brings cold water.

La Nina is currently in effect. Because summer temperatures are lower during La Nina, climate scientists worry about what a severe heat wave will look like during the next El Niño, while warmer summer weather is also expected.