It’s no coincidence that extreme heat is engulfing huge swaths of Asia, Europe and North America all at the same time. Powerful weather forces are combining to create the planetwide conditions, and there’s unlikely to be relief from the scorching temperatures anytime soon.
Climate change is at the heart of what’s boosting heat to new records. But there’s more to the picture. The way the Earth and the atmosphere are wired means that the weather in one location can influence conditions on the other side of the globe, with high and low pressure zones helping to create the links. The phenomenon is called teleconnections by meteorologists, and it all has to do with how air is moving around the atmosphere.
Those high and low pressure zones bring heat to some areas and flooding rains to others. Often, the systems drift over the globe. But right now, the carousel isn’t moving. It’s been cemented in place for weeks, and forecasts show it’s going to stay that way.
Blame the jet stream — the "meandering river of wind that encircles the globe and creates our weather,” as climate scientist Jennifer Francis puts it.
Right now, it’s "unusually stuck in place,” said Francis of the Woodwell Climate Research Center in Massachusetts. "The multiple devastating heat domes and flooding events around the Northern Hemisphere in recent weeks are indeed connected.”
The heat has had deadly consequences as domes of high pressure stay stagnant.
Record-setting temperatures were blamed for a surge of deaths in Mexico, and conditions were so extreme in California’s Death Valley National Park this week that a medical helicopter was unable to respond to the scene when a 71-year-old man was dying. Phoenix, the fifth-largest U.S. city, has seen a record 21 days with temperatures above 43 degrees Celsius. Wildfires have broken out across Greece and Switzerland, while Rome has seen all-time highs and Tokyo smashed a 150-year-old heat record.
Meanwhile, the low pressure systems are wreaking their own havoc as rains pour down. In India, months of blistering heat has given way to a deluge that has led to widespread damage. Floods are threatening Beijing and Tianjin in China, and two weekends in a row have brought deadly flooding to the U.S. Northeast.
The pressure systems are "like a chain,” said Paul Pastelok, senior meteorologist at commercial forecaster AccuWeather. "It is kind of like a lock and chain — everything is connected all the way across.”
One of the clearest examples of how the teleconnections work is seen with El Nino, the phenomenon in the equatorial Pacific that can upend weather patterns the world over. As surface waters become much warmer than usual, trade winds weaken or can even reverse. These changes then ripple around the globe. The world is now under its first El Nino weather in nearly four years.
Currently, high pressure over the southern U.S. has ensured low pressure will dominate the Northeast. The heat domes in North Africa and Asia have been followed by low pressure downstream, which has brought deadly floods to China and set rainfall records in Japan.
On top of all this, the oceans temperatures are also setting new highs.
"Once you get extremely warm oceans, it is easier to maintain heat waves” as more humidity gets unleashed, said Daniel Swain, a climatologist at the University of California Los Angeles.
Scientists are also looking into a hypothesis that says under certain conditions the waves in the jet streams can lead to high and low pressure systems being locked in place.
"And that would indeed be at least consistent with what we are seeing, at least times, this summer,” Swain said in a livestream presentation Wednesday. "It is still a hypothesis with a growing amount of evidence in its favor, but not an overwhelming amount — that’s my current personal assessment.” Still, he added, "it’s increasingly likely that there is” something to theory.