America's cruel summer

Driving the news: Blistering heat waves have struck all over the country; another one is now ramping up in the Southwest.

• Tens of millions of people have been exposed to dangerously poor air quality due to smoke billowing from Canada's record-breaking wildfires.
• Those fires could worsen this month, and some could even last through the winter by becoming "zombie fires" in the Far North, burning in the soils of peatlands.
• This week featured the world's hottest days on record. Even hotter extremes lie ahead from the one-two punch of El Niño and climate change.

Between the lines: To meteorologists and climate scientists who closely track the planet's "climate indicators," the simultaneous number of flashing red signs are ominous.

• The daily heat records set or tied this week have been astonishing, beating previous spikes that also occurred during 2016's El Niño conditions.
• The North Atlantic Ocean Basin's sea surface temperatures are at all-time record highs, leading some scientists to increase their forecasts for the number of hurricanes likely to form this season.
• Antarctic sea ice cover is at an all-time low.

Global monthly and daily temperatures are spiking off the charts, too.

• On Thursday, global average surface temperatures exceeded 63° Fahrenheit for the first time. Last month was the hottest June on record.
• This month will likely be the hottest July, and maybe the hottest month ever recorded, Zeke Hausfather, a climate scientist with Berkeley Earth and at Stripe, tells Axios.
• The heat waves across the country this summer have been long-lasting and deadly, the result of stagnant weather patterns featuring brutal heat domes locked in place for weeks at a time.

What's next: Another developing heat dome, this one setting up across the Southwest, looks to yield one of the longest, hottest heat waves on record in Arizona during the next two weeks. That includes Phoenix, the National Weather Service warns.

• "Temperatures across the region may be some of the hottest we have ever seen," forecasters wrote in an online briefing Friday. They also stated it could break a record for the longest-lasting heat wave in the region's history.
• It is possible that Phoenix will tie or exceed its all-time temperature record of 122°F, which would be an acute public health risk.

• Extreme heat is the deadliest weather-related hazard in a typical year across the U.S.

Context: Stronger areas of high pressure aloft, or heat domes, are a suspected hallmark of a warming climate. Studies show that heat waves are becoming more severe, longer lasting, and likely to occur as the global average temperature rises.

• Some studies have found that certain heat waves would have been virtually impossible in the absence of human-caused global warming.
• According to Michael Wehner of Lawrence Berkeley National Laboratory, climate change now makes typical heat waves about 5°F warmer than temperatures would have been in a preindustrial climate.
• The transition out of a cooling La Niña and into an El Niño, which tends to boost global average temperatures, has quickly manifested in record monthly temperatures, Hausfather told Axios in an email.

The bottom line: It is increasingly likely that both 2023 and 2024 will set records for the warmest years since instrument records began in the 1800s. In April, Hausfather wrote that there was only about a 22% chance that 2023 would eclipse 2016 as the warmest year on record.

• That has now increased to "roughly 77%," he said.
• "We expect 2024 to be even warmer, as the majority of the El Niño's effects will be felt then."