Scientists say a closely observed atmospheric pattern, the jet stream, is behind Canadian wildfires and scorching heat in Texas, raising questions about how it shapes extreme weather events and whether climate change is disrupting your flow.
The jet stream, a ribbon of air that encircles the Northern Hemisphere at high altitudes, causes pressure changes that determine the weather in North America. The wavy pattern of the jet stream creates areas of high and low pressure.
In recent months, jet stream patterns trapped and stalled a ridge of high pressure over northern Canada, sparking a heat wave and setting the stage for wildfires that later sent smoke into the Midwest and the eastern US Earlier this month, another high pressure ridge centered over Texas, raising temperatures.
More than 100 million people in the US faced scorching heat or unhealthy air quality on Wednesday.
In recent weeks, the jet stream has appeared unusual and disjointed, scientists say. Some researchers believe that climate change is disrupting its flow and causing regions to warm longer. They worry that changing patterns could cause extremes to rise more rapidly than climate models have projected as the world warms.
Michael Mann, a climate scientist at Pennsylvania State University, likened visualizations of the jet stream’s appearance in recent weeks to the swirling brushstrokes of a Post-Impressionist painter.
«I honestly don’t know how to characterize the current pattern of large-scale planetary waves,» Mann tweeted this month. «Frankly, he looks like a Van Gogh.»
Those weather patterns are of particular interest to climate scientists because they add to research suggesting that alterations in jet stream patterns could play an important role in driving extreme conditions.
Jennifer Francis, a senior scientist at the Woodwell Climate Research Center in Massachusetts, said recent weather patterns fit that theory.
“Climate change is pushing heat waves into more extreme territory every year,” Francis said. In a warming world, he added, «these kinds of wavy and blocky patterns» in the jet stream «are certainly consistent with what we expect to see more often.»
Whether a warmer atmosphere is messing with the jet stream has not been tested. Researchers are still investigating whether there is a link between climate change and the jet stream and how those specific weather events fit together.
Some scientists, like Francis, believe that global warming is causing the jet stream to become increasingly wavy.
But Kai Kornhuber, an associate research scientist at Columbia University and principal scientist at Climate Analytics, a nonprofit policy institute, said the theory is unproven and difficult to test. The trends don’t stand out clearly in the available data, he said.
However, Kornhuber and Francis agree that there is evidence that rising global temperatures are causing the jet stream to slow and trap high-pressure systems like those in Canada and Texas.
“We see more persistent weather patterns, and persistence translates to greater impacts,” Kornhuber said.
Longer heat waves challenge people’s heat tolerance and also dry out soils and warm the land, which can reinforce the jet stream pattern and create a self-fulfilling cycle.
«Once the heat wave sets in over the land and the land warms up, it’s the hot air that causes the atmosphere to swell,» said John Walsh, chief scientist at the International Arctic Research Center at the University of Alaska Fairbanks. «There is a positive feedback loop that contributes to the persistence and intensity of the heat wave.»
Scientists are still figuring out how global warming might affect the jet stream and what mechanisms might be responsible for the most significant changes. Francis said rising ocean temperatures and melting sea ice in the polar regions could be contributing.
There is no question that heat waves are increasing in severity and frequency.
«Heat extremes scale with average temperature,» Kornhuber said.
Changes in the nature of the atmospheric circulation and jet stream could intensify those trends even more and faster than scientists thought.
“We need to consider whether climate models are more conservative when it comes to extreme weather conditions,” Kornhuber said.