What is behind the heat waves affecting the United States?

July 24 – All the contiguous United States experienced above-average temperatures in the past week, with the more dangerously hot weather forecast. read more.

The U.S. heat wave followed record heat that killed hundreds if not thousands of people and sparked wildfires in Europe.

According to scientists, the following is an explanation of what is causing the heat waves.


A heat wave has no single scientific definition. Depending on the region’s climate, it can be determined by a certain number of days above a specific temperature or percentile of the norm.


The Arctic is warming three to four times faster than the globe, meaning there is less difference between northern temperatures and those closer to the equator.

According to Jennifer Francis, senior scientist at the Woodwell Climate Research Center, that results in swings in the North Atlantic jet stream, which leads to extreme weather events like heat waves and floods.


Warmer oceans contribute to heat domes, which trap heat over large geographical areas. This weekend the heat dome is stretching from the southern plains of the Oklahoma/Arkansas area to the eastern seaboard, according to the U.S. Weather Prediction Center.

Scientists have found the leading cause of heat domes is a substantial change in ocean temperatures from west to east in the tropical Pacific Ocean during the preceding winter.

“As prevailing winds move the hot air east, the northern shifts of the jet stream trap the air and move it toward land, where it sinks, resulting in heat waves,” the U.S. National Oceanic and Atmospheric Administration says on its website.


Every few years, the climate patterns are known as El Niño and, less frequently, La Niña occurs. El Niño brings warm water from the equatorial Pacific Ocean up to the western coast of North America, and La Niña brings colder water.

At present, La Niña is in effect. Because summer temperatures trend lower during La Niña, climate scientists are concerned about what a severe heat wave would look like during the next El Niño, when even hotter summer weather could be expected.


Scientists say that climate change caused by the burning of fossil fuels is a global phenomenon that is certainly playing a role in what the United States is experiencing.

“Climate change is making extreme and unprecedented heat events both more intense and more common, pretty much universally throughout the world,” said Daniel Swain, a climate scientist at UCLA.

“Heat waves are probably the most underestimated type of potential disaster because they routinely kill a lot of people. And we just don’t hear about it because it doesn’t kill them in, to put it bluntly, sufficiently dramatic ways. There aren’t bodies on the street.”

Francis of the Woodwell Center said with climate change, the world is seeing changing wind patterns and weather systems “in ways that make these heat waves like we’re seeing right now, more intense, more persistent, and cover areas that just aren’t used to having heat waves.”

Alex Ruane, the researcher at NASA’s Goddard Institute for Space Studies, said as the world warms, “it takes less of a natural anomaly to push us into the extreme heat categories. Because we’re closer to those thresholds, it’s more likely that you’ll get more than one heat wave at the same time. We’re seeing this in the United States.”

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