Virtually all of the contiguous United States has experienced above-normal temperatures in the past week, with more dangerous weather forecast.
The heat wave in the US followed record heat that killed hundreds if not thousands of people and sparked wildfires in Europe.
The following is an explanation of what causes heat waves, according to scientists.
A heat wave does not have a single scientific definition. Depending on the climate of a region, it can be determined by a certain number of days above a specific temperature or percentile of the norm.
Arctic warming and jet stream migration
The Arctic is warming three to four times faster than the globe as a whole, which means that there is less and less difference between the temperatures in the north and those closer to the equator.
This results in oscillations in the North Atlantic jet stream, which in turn leads to extreme weather events such as heat waves and floods, according to Jennifer Francis, senior scientist at the Woodwell Climate Research Center.
Warmer oceans contribute to heat domes, which trap heat over large geographic areas. This weekend, the heat dome will stretch from the southern plains of the Oklahoma/Arkansas area up the East Coast, according to the U.S. Weather Forecast Center.
Scientists have found that the main cause of the heat domes is a strong change in ocean temperature from west to east in the tropical Pacific Ocean during the previous winter.
“As the prevailing winds move the warm air to the east, the northern turns of the jet stream trap the air and move it towards the land, where it sinks, resulting in heat waves,” says the National Administration of the United States Ocean and Atmospheric on their website.
Every few years, the weather patterns known as El Niño and, less frequently, La Niña. El Niño brings warm water from the equatorial Pacific Ocean to the west coast of North America, and La Niña brings cooler water.
Currently, La Niña is in effect. Because summer temperatures tend to be lower during La Niña, climate scientists are concerned about what a serious heat wave will be during the next El Niño, when even hotter summer weather could be expected.
Climate change caused by the burning of fossil fuels is a global phenomenon that certainly plays a role in what the United States is experiencing, scientists say.
“Climate change is making extreme and unprecedented heat events more intense and more common, almost universal around the world,” said Daniel Swain, a climate scientist at UCLA.
“Heat waves are probably the most underrated 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, to put it bluntly, in pretty dramatic ways. No bodies in the street.”
Francis, of the Woodwell Center, said that with climate change the world is seeing wind patterns and weather systems changing “in ways that make these heat waves, as we’re seeing now, more intense, more persistent, and cover the areas that are alone. I’m not used to having heat waves.”
Alex Ruane, researcher at NASA’s Goddard Institute for Space Studies, said that when the world warms, “it takes less than a natural anomaly to push it into the categories of extreme heat. Because we are closer to those thresholds, it is more likely than you “We will have more than one heat wave at the same time. We see this in the United States.”
