The oppressive heat wave roasting Texas and Mexico is rekindling a scientific debate about the effects that Arctic climate change might have on weather patterns around the world.

Many experts say that rapid warming in the Arctic — where temperatures are rising four times faster than the global average — may cause an increase in these kinds of long-lasting extreme weather events.

It all comes down to the jet stream, a fast-flowing air current that wraps around the Northern Hemisphere. Many researchers theorize that rising temperatures in the Arctic are altering the atmosphere in ways that disrupt the jet stream’s flow, causing it to dip and meander up and down as it zooms around the globe. A wavier jet stream can cause heat waves, storms and other weather systems to get stuck in place, dragging out for days or weeks on end.

That’s what has happened in Texas and Mexico this month.

An unusual dip in the jet stream caused a persistent high-pressure weather system, known as a “heat dome,” to form over the region and trap hot air. It’s already baked the region with record-breaking heat for two weeks, and it’s expected to drag out for another week or so, likely creeping into neighboring states in the coming days.

A number of factors likely influenced this event, including a brewing El Niño. But some scientists say these wobbly jet streams may happen more often as Arctic temperatures continue to soar.

“This is exactly the type of pattern — that is, extremely wavy and thus persistent — that we expect to see more frequently as the Arctic warms now about four times faster than the globe as a whole,” said Jennifer Francis, a senior scientist at Woodwell Climate Research Center, in an email to E&E News.

The Texas event already has clear connections to climate change thanks to the sheer intensity of its heat. Temperatures have soared as high as 118 degrees, just 2 degrees shy of the state’s all-time heat record.

Some cities have tied or broken local records, including San Angelo at 114 degrees June 20 and Laredo at 115 degrees. And the heat index — a metric that accounts for both temperatures and humidity — has soared across the state, making temperatures feel well above 120 degrees in some places. Austin broke its all-time heat index record at 118 degrees Wednesday. And Corpus Christi hit a staggering heat index of 125 degrees.

Jet stream and wildfire smoke

As global temperatures rise, heat waves are becoming more frequent and more intense all over the planet. The background warming can help explain why some events, like the one in Texas, are becoming so extreme.

The science communication nonprofit Climate Central has developed a tool it calls the Climate Shift Index, which compares the likelihood of an extreme temperature event today versus the likelihood of the same event in a world without human-caused climate change. The index suggests that the recent temperatures in southern Texas are at least five times more likely to occur.

The heat is blistering, even for Texas. Yet it’s not just the temperatures that are causing mayhem. It’s also how long they’re dragging out — in a relatively unusual location for a heat dome during this time of the year.

That’s due to this summer’s wonky jet stream. It has split into two branches in recent weeks, meandering in large, looping patterns over North America that can cause weather patterns to get stuck in place.

The Texas heat dome isn’t the only one. There’s also a heat dome over Alberta and other parts of central Canada, and the jet stream helped drive wildfire smoke from Canada down into the eastern U.S. earlier this month.

The exact drivers of the wacky air currents are still up for debate. The jet stream naturally wanders or splits sometimes without the influence of other factors like human-caused climate change. And a brewing El Niño event could also be playing a role.

El Niño is a natural climate pattern that causes temporary warming in parts of the Pacific Ocean, affecting weather events all over the world. It typically recurs every two to seven years. NOAA scientists recently announced the arrival of El Niño, which is expected to strengthen throughout the year.

El Niño events generally shift the jet stream southward and have been known to cause the current to split. These effects tend to be most pronounced in winter, sometimes diverting storms toward the southern U.S.

Climate change may also be playing a part in the jet stream’s behavior.

Because the Arctic is heating up so quickly, it’s changing the relationship between temperatures at the top of the world and those closer to the equator. Air temperatures affect the thickness of the atmosphere and the way air currents flow around the planet.

As the temperature gradient changes, some scientists theorize that the jet stream may become wavier and more meandering as it circles the globe. That can cause aggressive dips and splits in the current, like the patterns it’s exhibited this summer.

These patterns are often associated with persistent storms or heat waves that get stuck in place and drag on for days or weeks. The Texas heat wave is a prime example, but other places are affected, too.

Wonky jet streams have been linked to severe weather events around the world. A study last year found that split or “double” jet streams are associated with extreme heat in Europe. And a 2019 study found that large waves in the atmosphere can cause long-lasting extreme heat and severe rainfall from North America and Europe to the Middle East and Japan.

Some researchers have suggested that while the jet stream may be changing as the planet warms, other factors outside the Arctic could also be to blame.

A 2018 review paper looked specifically at the links between the warming Arctic and extreme summer weather throughout the Northern Hemisphere. It concluded that many questions remain about the exact mechanisms — but some connections likely do exist.

Summer weather has been less of a focus than winter weather and deserves more attention, the authors of the study said, adding that “a scientific consensus is emerging that [Arctic warming] has at least some influence on winter weather.”

In general, the links between Arctic warming and the jet stream are growing more clear, according to Francis, a top researcher on the topic.

“The exact connections between rapid Arctic warming and the jet stream are still incompletely understood, but I think it’s safe to say that no one believes the Arctic can warm four times faster than the globe and NOT affect the jet stream,” she said in an email.

The combination of human-caused climate change on top of natural climate patterns like El Niño can cause even greater extremes. And these combinations are likely to grow even more intense in the future as the planet keeps on warming.

“The present conditions have never occurred before as long as records have been kept,” Francis said. “As we dig deeper into this research the story gets only more complicated, but it’s a fascinating time to be a scientist in this field!”