Kristina Dahl, a senior climate scientist at the Union of Concerned Scientists, says the heat wave is “unprecedented.”

Michael E. Mann, a climate scientist at Pennsylvania State University, put it very simply: climate change is making heat waves more frequent and more intense. “You warm up the planet, you’re going to see an increased incidence of heat extremes,” Mann told CNN.

Experts like Dahl and Mann say climate change is reshaping the planet’s weather patterns. As humans emit more planet-warming greenhouse gas into the atmosphere, more energy is added to the climate system. The excess energy, according to Kristie Ebi, a climate and health researcher at the University of Washington, appears by way of extreme weather events.

“Heat waves have always occurred and will always occur, but we’ve got a very different pattern of heat waves now than we did a couple of decades ago,” Ebi told CNN. “And it’s not just the intensity, it’s also the geographic extent.”

In the opposite end of the country, over 40 million people in the Northeast US are also under heat advisories, including the New York, Philadelphia and Boston metropolitan areas. Though the heat won’t be as bad as Oregon and Washington, records for the date could be set in the Northeast before temperatures cool off on Thursday.

“Heat likely contributes to many more deaths from causes other than heat stroke, because heat can exacerbate other chronic diseases, such as heart and lung conditions,” Weinberger told CNN. “Given the danger posed by heat, events like the ongoing heat wave in the Pacific Northwest need to be taken very seriously.”

“Normally we would expect about 1 or 2 visits for heat illness in the same time period,” Kate Yeiser, communications coordinator for Multnomah County, told CNN in an email. “The visits this weekend alone represent nearly half the heat illness visits we typically see during an entire summer.”

One appalling aspect of heat-related deaths in the US is the number of premature mortalities brought by heat exposure, particularly among babies and children left unattended in cars.

“Many don’t understand how fast cars heat up and how babies physiology can’t tolerate that,” Ebi said. “Ensuring that people are really aware about protecting babies and children during these heat waves is important.”

To understand how the climate crisis is changing the playing field, Mann suggests thinking of weather events on a bell curve. The highest point of the curve is where the most common weather takes place and the tails are where the extreme events lie. A warming planet shifts the bell curve to the right, pushing the already-extreme events into uncharted territory.

Mann says that climate models, which predict general global conditions well into the future, can well-capture the shift and predict increases in extreme heat. But, he said, they do not paint a full picture of the impacts of climate change during the summer.

“In that sense, climate models are actually underestimating the impact that climate change is having on events like the unprecedented heat wave we’re witnessing out West right now,” Mann added.

Climate change can cause the jet stream to get locked into a static wave pattern during the summer. Daniel Swain, a climate researcher at the University of California at Los Angeles, says this is best illustrated by flicking a jump rope up and down until its waves seem to stand still. Similarly in the atmosphere, high and low pressure systems can get stuck, creating extreme weather events like severe heat, drought or wildfires.

That’s what happened in the Pacific Northwest this weekend, where a so-called heat dome, a strong ridge of high pressure, acts as a lid on the atmosphere. The lid traps the hot air trying to escape, and warms it even more as it sinks.

“Even if the jet stream does what it historically used to do, with no specific climate change contributions, climate change is still dramatically increasing the likelihood of these extreme heat events,” Swain told CNN. “If you warm the atmosphere, you’d expect those heat waves to be hotter than they otherwise would have been.”

If the US fails to slash planet-warming emissions and improve climate adaptation systems, climate experts say people across the US and around the world are going to experience more severe impacts of extreme heat.

“When we look at where we’re heading in the future, our analysis has shown that if we fail to reduce our heat-trapping emissions, we are poised to see a staggering expansion of dangerous heat across the US,” Dahl told CNN.

But, she adds, if the US aggressively reduces emissions as well as limit future global warming to 2-degrees Celsius, we can “spare millions of people in the US and many more around the world from relentless summer heat.”