Extreme heat also increases the risk of wildfires. Lachun fire, a 350-acre fire
In California’s Sequoia National Forest, 35% were under control. Chart: https://tmsnrt.rs/3T9z9BB
Here are some of the factors that drive heat waves, according to scientists.
Climate change caused by human activity
Scientists say climate change, caused by the combustion of fossil fuels, is a global phenomenon that certainly plays a role in what is plaguing the United States.
“Climate change is making extreme and unprecedented thermal events more intense and more general around the world,” said Daniel Swain, a climate scientist at the University of California, Los Angeles.
“Heatwaves are probably the most underrated type of potential disaster because they routinely kill so many people. And we don’t hear about them because they don’t die dramatic enough, frankly,” Swain said.
Climate change is causing the world to see wind patterns and weather systems change in ways that make heat waves more intense, continuous and pervasive, said Jennifer Francis, chief scientist at the Woodwell Center for Climate Research.
As the world warms, fewer natural anomalies are needed to cause extreme heat classes, said Alex Rowan, a researcher at NASA’s Goddard Institute for Space Studies.
“Because we’re closer to that boundary, you’re more likely to get more than one heat wave at a time. We’re seeing that in the US right now.”
Arctic warming and current migration
The Arctic is warming three to four times faster than the Earth as a whole, which means there is less and less difference between temperatures in the north and temperatures closer to the equator.
This leads to fluctuations in the North Atlantic jet stream, which in turn lead to extreme weather events such as heat waves and floods, Francis of the Woodwell Climate Research Center said.
Warmer oceans contribute to heating domes, which trap heat over wide geographical areas.
Scientists say the main cause of thermal domes is the sharp change in ocean temperatures from west to east that occurred in the tropical Pacific during the previous winter.
“While prevailing winds move warm air eastward, shifts of the jet stream northward trap the air and move it toward Earth, where it sinks, causing heat waves,” the US National Oceanic and Atmospheric Administration said in an online statement.
El Nino or Nina
Every few years, weather patterns known as El Nino and, less commonly, La Nina, occur. El Nino brings warm waters from the tropical Pacific to the west coast of North America, and La Nina brings cold waters.
La Nina is currently in effect. As summer temperatures drop during La Nina, climate scientists are concerned about what an extreme heat wave will look like during the next El Niño, while warmer summer weather is expected.
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