Climate change is supercharging a hot and dangerous summer.
In the town of Sodankyla, Finland, the thermometer on July 17 registered a record-breaking 90 degrees, a remarkable figure given that Sodankyla is 59 miles north of the Arctic Circle, in a region known for winter snowmobiling and an abundance of reindeer.
Greece is in mourning after scorching heat and high winds fueled wildfires that have killed more than 80 people. J
Japan recorded its highest temperature in history, 106 degrees, in a heat wave that killed 65 people in a week and hospitalized 22,000, shortly after catastrophic flooding killed 200.
Montreal hit 98 degrees on July 2, its warmest temperature ever measured. Canadian health officials estimate as many as 70 people died in that heat wave.
In the United States, 35 weather stations in the past month have set new marks for warm overnight temperatures.
The brutal weather has been supercharged by human-induced climate change, scientists say. Climate models for three decades have predicted exactly what the world is seeing this summer.
And they predict that it will get hotter - and that what is a record today could someday be the norm.
"The old records belong to a world that no longer exists," said Martin Hoerling, a research meteorologist at the National Oceanic and Atmospheric Administration.
It's not just heat. A warming world is prone to multiple types of extreme weather - heavier downpours, stronger hurricanes, longer droughts.
"You see roads melting, airplanes not being able to take off, there's not enough water," said Katharine Hayhoe, director of the Climate Science Center at Texas Tech University. "Climate change hits us at our Achilles' heel.
The proximate cause of the Northern Hemisphere bake-off is the unusual behavior of the jet stream, a wavy track of west-to-east-prevailing wind at high altitude.
The jet stream controls broad weather patterns, such as high-pressure and low-pressure systems.
This summer, the jet stream has undulated in extreme waves that have tended to block weather systems from migrating. The result has been stagnant high-pressure and low-pressure systems with dire results, such as heat waves in some places and flooding elsewhere.
"When those waves are very big - as they have been for the past few weeks - they tend to get stuck in place," said Jennifer Francis, a professor of atmospheric science at Rutgers University. Last year, scientists published evidence that the conditions leading up to "stuck jet streams" are becoming more common, with warming in the Arctic seen as a likely culprit.
Last year, when Hurricane Harvey broke the record for how much rain could fall from a single storm, researchers knew climate change had been a factor.
Theory, meet reality: When the atmosphere is warmer, it can hold more moisture. Climate change does not cause hurricanes to spin up or thunderstorms to develop, but it can be an intensifier.
The heat waves have hit hard where people don't expect them - the Netherlands, Sweden, Britain, Ireland and Canada.
It's Britain's driest summer since modern records began in 1961. Reservoirs are declining rapidly, and water restrictions are in effect. The United Kingdom's national weather service urged people to avoid the sun this week, with temperatures expected to hit 98 Fahrenheit.
In Ireland, the sun-parched fields revealed a previously hidden footprint of a 5,000-year-old monument near Newgrange.
Human activity, primarily the burning of fossil fuels, has added greenhouse gases to the atmosphere,trapping heat and making extreme weather events even more extreme.
The amount of carbon dioxide in the atmosphere reached 410 parts per million in May, the highest since Charles David Keeling started keeping records in 1958.
Kevin Trenberth, a climate scientist with the National Center for Atmospheric Research, said even modest heat from global warming can build up over time.
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The Washington Post