Axios

Unprecedented fires have already torched millions of acres throughout Canada during its worst-on-record wildfire season — which is long from over.

Why it matters: Smoke from the fires has so far triggered air quality alerts in hundreds of cities across North America. But with the typical peak of wildfire season still ahead, dangerous, haze-filled skylines may be a common sight this summer.

The heat wave scorching much of the U.S., along with dangerously poor air quality from wildfire smoke, is giving Americans a preview of the compound climate disasters that experts fear will become increasingly common as the planet warms.

Why it matters: Extreme heat and hazardous air quality are acute public health threats, and the heat has already proven deadly.

Air quality alerts were issued in cities across some 23 U.S. states Thursday as lingering smoke from Canada's worst-ever wildfire season continued to pose a health threat to millions of Americans.

The big picture: Detroit, D.C., New York City and Toronto endured some of the world's worst air quality Thursday, per Swiss air technology company IQAir. Alerts stretched from Colorado to Vermont and down to Georgia. Canadian officials warn this extreme weather event will likely last all summer as climate change leads to more instances of critical fire weather.

As the oppressive hot weather that Texans have endured for weeks spreads across the U.S., Californians were preparing for their first major summer heat wave Friday.

State of play: Extreme heat was expected from central California into the desert Southwest Friday into this weekend, with excessive heat warnings issued by the National Weather Service for Californian cities including Los Angeles and San Diego.

The hunt for dark matter and dark energy in the universe is expanding.

The big picture: Gravity from dark matter holds gas and dust together in stars and galaxies while dark energy pushes galaxies away from one another. Together, scientists think they make up 95 percent of our universe but what exactly they are remains elusive.

Virgin Galactic successfully launched its first commercial suborbital mission on Thursday, sending a crew of six to the edge of space.

Why it matters: This start of commercial service has been a long time coming for the company, which Richard Branson founded in 2004.

Much of the U.S. is under siege from extreme weather.

The big picture: Heat warnings and watches are in effect for over 100 million people as a record-breaking heat wave sweeping the southern U.S. continues to expand. Meanwhile, air quality alerts have been issued for an estimated 80 million others as wildfire smoke from Canada chokes much of the Mid-Atlantic, Midwest, Ohio Valley and even the Southeast.

Firefighters in Canada are now battling 497 active wildfires across the country after 31 new blazes ignited, according to the latest data from the Canadian Interagency Forest Fire Centre.

The big picture: New figures show 3,023 fires have burned across some 19.7 million acres of land during what officials this week declared has been Canada's worst wildfire season on record.