Same force behind Texas deep freeze could drive prolonged heat waves

The jury is still out on whether climate change is playing a role in the brutal cold, snow, and ice that have wreaked havoc across Texas this week, cutting power to millions of Texans, bursting pipes, and contaminating water supplies. But the same climate connection scientists are debating—Arctic warming causing the jet stream to meander further south—might also cause the southern United States to experience more persistent heat waves in the future.

That’s according to research published last month in Geophysical Research Letters that addresses the poorly studied question of whether enhanced Arctic warming, or “Arctic amplification,” will lead to longer lasting hot weather spells at lower latitudes. Using a new approach of tracking weather systems to see how quickly they move, the researchers identified a link between slower-moving summer weather patterns and a smaller temperature difference between the equator and the Arctic, caused by the latter warming more rapidly.

If that trend continues, heat waves might become significantly more persistent over the next 70 years or so, particularly in regions like the southern U.S. Given that future heat waves are also expected to be hotter, the research points to a potential double atmospheric whammy that could strain societies’ ability to cope: hotter weather that sticks around longer.

“This study supports the hypothesis that rapid Arctic warming will favor more persistent summer weather, which often leads to the very extremes making headlines in recent years: prolonged heat waves, droughts, and rainfall,” says Woodwell Climate Research Center senior scientist Jennifer Francis, who wasn’t involved in the new study.

While prolonged heat waves are the opposite of what the southern U.S. is experiencing this week, the mechanisms involved could be similar—and the challenges to the electric grid and human well-being just as severe.

The Arctic-mid-latitude weather connection

The Arctic is warming more than twice as quickly as the rest of the world, partly due to feedback loops caused by melting ice and snow, which expose darker ocean and land surfaces that absorb more solar energy and increase melting even more. This Arctic amplification effect narrows the temperature difference between the Arctic and mid-latitude regions like the continental U.S. That temperature difference is what powers the jet stream—a fast-flowing river of air that sends weather systems snaking eastward across the Northern Hemisphere. Seminal research by Francis suggests that Arctic warming may already be causing the jet stream to become slower and wavier.

If Arctic amplification is influencing the jet stream in this way, there could be widespread impacts on weather across vast swaths of North America and Eurasia. In particular, a flurry of recent studies have explored whether a weaker, wavier jet stream could lead to more Arctic air intrusions at low latitudes like the extreme cold spell gripping vast swaths of the country this week. 

However, these connections are contentious. While scientists generally agree that Arctic warming can influence the jet stream, there is little consensus on whether the jet stream has already experienced significant changes due to climate change, how extreme any future changes will be, or how much of an effect that will have on mid-latitude weather.

Complicating matters further, the direction of influence might go both ways: A study published last year suggested that random fluctuations in the jet stream might be enhancing Arctic warming by transporting heat and moisture from mid-latitudes north.

“Causality could work in either direction, mid-latitudes affecting the Arctic or Arctic affecting mid-latitudes,” James Screen, a climate scientist at the University of Exeter who co-authored the 2020 paper, wrote in an email. “Much of the current debate in this uncertain topic hinges on the relative sizes of these two effects.”

A summer weather connection?

If the connection between Arctic warming and cold air outbreaks is murky, scientists know even less about whether a wavier jet stream will influence summer weather patterns like heat waves. But that’s a topic that deserves attention, especially since heat waves are expected to get more severe in the future due simply to the warming atmosphere, while cold extremes are projected to become less intense due to climate change.

“Summer heat waves are just a really dangerous thing,” says Kai Kornhuber, a postdoctoral researcher at the Columbia University Earth Institute. “They’re not really seen this way because many people still associate [them] with nice warm weather and holidays, but they’re one of the most deadly natural phenomena.”

To explore the connection between dangerous summer weather and rapid Arctic warming, Kornhuber and his colleague Talia Tamarin‐Brodsky of the University of Reading in the U.K. used a weather-tracking algorithm to gauge how quickly summer weather patterns and temperature anomalies move across the Northern Hemisphere and how that relates to the temperature gradient between the equator and the poles. They found that in recent decades, when the temperature difference between mid-latitudes and the Arctic was smaller, that correlated with summer weather hanging around longer in one place.

Their research suggests the effect could become far more pronounced in the future. Under a high-carbon-emissions scenario called RCP 8.5, in which the world completely fails to rein in its carbon emissions, some climate models project the Arctic-mid-latitude temperature difference will shrink much further. If that happens, Kornhuber and Tamarin-Brodsky found, summer weather patterns could slow by as much as 11 percent across Europe and 33 percent across Russia by the end of the century. In southern North America, systems could slow as much as 58 percent—causing heat waves to linger in one place that much longer.

While the study isn’t the first to suggest that Arctic amplification may be leading to more sluggish, hot weather, “this area of research is quite novel,” says Judah Cohen, the Director of Seasonal Forecasting at Atmospheric and Environmental Research, a weather consultancy. The paper “helps part the clouds in a hazy area of research” by applying a “novel approach” to track the movement of summertime weather systems, Francis says.                                                           

Correlation, but not causation

The findings have some important caveats. While the authors found a link between a warming Arctic and slower summer weather, their results—like much of the research on Arctic amplification and cold air outbreaks in winter—don’t prove that the former causes the latter. Future research will be needed to demonstrate any causal links to Arctic warming and the jet stream.

Even if rapid Arctic warming does lead to more stalled summer weather patterns further south, it’s unlikely that it will be the sole factor at play. “There are many factors that influence [weather] persistence, and the temperature gradient might not be the dominant one,” Screen says.

As Kornhuber and Tamarin-Brodsky note in their paper, not all climate models agree that the Arctic amplification effect will continue to grow more intense in the summer. But even in scenarios where the equator-to-pole temperature difference begins growing again—implying a reduced Arctic amplification effect—the authors’ models still project summer weather patterns slowing down in North America.

Kornhuber says the most likely explanation is another consequence of climate change, separate from what’s happening in the Arctic: As the planet warms, mid-latitude storm tracks are projected to shift northward. In the future, Kornhuber says, southwestern North America “is projected to not be in the center of these strong winds, but to the south of it, which also increases weather persistence,” as the storms escape the winds that would move them on.

All in all, the new research suggests that the U.S. is likely to see more slow-moving heat waves in the future, even if the mechanisms aren’t yet clear. With this week’s weather reminding us that severe cold spells aren’t going away, the best way to prepare for climate change may be to beef up heating and cooling systems at the same time—and to prepare the electric grid for temperature extremes in both directions.

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