When will the heat end? Never.

By Mary Gilbert, CNN Meteorologist

(CNN) — Summer is off to a sweltering start after multiple record-breaking heat events sent temperatures soaring for millions of people in the US.

So when will it end?

Forecasts for the coming weeks and months show exceptional heat is largely here to stay, with only fleeting periods of respite. And the sobering summer reality on a planet warming due to fossil fuel pollution is the heat isn’t going anywhere – it’s only going to get more frequent and intense as global temperatures rise.

“Summers like the one we are experiencing now and the summer we had last year – which was the hottest on record – are going to become par for the course in the years ahead,” said Kristina Dahl, a climate scientist with the Union of Concerned Scientists.

A sign of things to come

There will still be colder-than-average summers in the future, but climate change is making it likelier more summers will end up hotter-than-average, Dahl told CNN. And the fingerprints of a changing climate are already visible, even before summer has reached its hottest months.

This spring, hundreds of cities in the eastern half of the US experienced one of their 10 hottest Mays on record in what was another sign of a changing climate: dangerous heat seeping into typically cooler seasons.

Early season heat waves add to the danger of what’s already the deadliest weather threat because the body can’t gradually acclimatize, or cope better with the heat, Dahl explained.

Acclimation or not, the abnormally hot temperatures are also altering the perception of what’s hot. Temperatures through at least midweek will climb up to 10 degrees above normal in parts of the western and southern US, but that pales in comparison to last week’s roasting conditions.

Summer should be hot, just not this hot: Parts of the central and eastern US sweltered through temperatures 25 or 30 degrees above normal last week. The heat was so extreme Caribou, Maine, a town just 10 miles from the Canadian border, hit 96 degrees, tying its all-time record high temperature.

“This is not your grandmother’s heat, this is significantly different,” Dahl said. “This (heat) really isn’t normal and it’s measurably influenced by climate change.”

The hottest is yet to come

Forecasts for the next few weeks, the next month and the rest of the summer all show one trend clearer than anything else: hotter-than-average temperatures for large sections of the US.

Above average temperatures are expected into early July for a vast majority of the Lower 48 with the exception of states along the northernmost tier of the country, according to forecasts from the Climate Prediction Center.

July is typically the hottest month of the year, but it is expected to be even hotter than normal this summer in almost every state.

Most of the East and parts of the Rockies are likely to be the most anomalously warm areas next month. This prolonged heat could be record-breaking.

Last July in Phoenix was the hottest month ever experienced in any US city. The city’s average July temperature – calculated based on both high and low temperatures for the month – was an astonishing 102.7 degrees.

Heat in Phoenix last summer wasn’t just extreme, it was long-lasting. Its longevity and dangerously high daytime and overnight temperatures took a toll on human health. The scorching July contributed to the deadliest year for heat in Maricopa County, where Phoenix is located, since officials began keeping records in 2003.

Heat lasted well beyond July last summer for much of the US.

A series of unrelenting heat domes baked huge parts of the country with the effects of each worsened by the one before. Every heat dome that parked over part of the country roasted the ground, dried out soils and made subsequent temperatures even hotter.

This year looks to be no different. Warmer-than-normal conditions are expected to extend through the summer and most of the fall, according to the CPC.

Warmer-than-normal falls aren’t nearly as dangerous as hot summers. But the cooler seasons only mask the lingering threat of extreme heat as long as global temperatures continue to rise, which scientists say can only be mitigated by dramatically reducing or phasing out planet-polluting fossil fuel use.

“The more we try to normalize (heat), the greater the danger we have of taking our eye off the ball in terms of what needs to be done to address climate change,” Dahl said.

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