(AP) — From the normally chilly Russian Arctic to the traditionally sweltering American South, big swaths of the Northern Hemisphere continued to sizzle with extreme heat as the start of summer more resembled the dog days of August with parts of China and Japan setting all-time heat records Friday.

In the United States, a heat dome of triple-digit temperatures in many places combined with high humidity oscillated from west to east. On Thursday, at least 15 states hit 100 degrees and at least 21 high-temperature marks were set or broken, according to the National Weather Service, which held 30 million Americans under some kind of heat advisory.

The extreme discomfort of Thursday came after 12 states broke the 100-degree mark on Wednesday and 21 records were tied or broken. Since June 15, at least 113 automated weather stations have tied or broken hot-temperature records. Scientists say this early baking has all the hallmarks of climate change.

In China’s northern Henan province Friday, Xuchang hit 107.8 degrees and Dengfeng hit 106.9 degrees for their hottest days on record, according to global extreme weather tracker Maximiliano Herrera. And in Japan Friday, Tokamachi and Tsunan set all-time heat records while several cities broke monthly marks, he said.

“It’s easy to look at these figures and forget the immense misery they represent. People who can’t afford air conditioning and people who work outdoors have only one option, to suffer,” said Texas A&M climate scientist Andrew Dessler, who was in College Station, where the temperature tied a record at 102 degrees Thursday. “Those of us with air conditioning may not physically suffer, but we are prisoners of the indoors.”

After three deaths, Chicago has changed its cooling rules.

In Macon, Georgia, the temperature swept from 64 degrees to 105 in just nine hours Wednesday. Then on Thursday, the temperature peaked at 104, a record for the day. Even Minneapolis hit 100 on Monday.

Probably only the Pacific Northwest and Northeast have been spared the heat wave, said National Weather Service meteorologist Marc Chenard at the Weather Prediction Center. On Thursday, Texas, Louisiana, Mississippi, Alabama, Georgia, Florida, Arizona, South Carolina, Arkansas, Oklahoma, Kansas, South Dakota, Colorado, Nevada and California all hit at least 100. Houston, Dallas, Austin, New Orleans and Orlando all tied high record marks on Thursday.

“It’s persistent,” Chenard said. “It’s been over a week and it’s going to continue in some aspects.”

It’s not just the U.S.

The Russian city of Norilsk, above the Arctic circle, hit 89.6 degrees Thursday for its hottest June day on record and tied for its hottest day in any month on record, according to Herrera. Saragt in Turkmenistan rose to 114.6 degrees but Herrera said in the next days it can get even worse.

Herrera said tracking heat records is so overwhelming that he doesn’t have time to eat or sleep.

A European heat wave has also caused problems with fires in Germany and Spain.

Northern Illinois University meteorology professor Victor Gensini said what’s happening with this early heat wave is “very consistent with what we’d expect in a continually warming world.”

“These temperatures are occurring with only 2 degrees Fahrenheit of global warming and we are on track for 4 degrees Fahrenheit more warming over this century,” Dessler said. “I literally cannot imagine how bad that will be.”

In Raleigh, North Carolina, it hit 100 on Wednesday and usually, the city only gets one 100-degree day a year, but it comes much later than this, said state climatologist Kathie Dello.

“In the southeastern U.S. many lack access to sufficient or stable cooling or cannot afford to use their home cooling systems. Heat morbidity and mortality is among our greatest public health risks in a changing climate.”

There may be some cooling by the weekend or Monday in some places, including the north-central part of the country, Chenard said. But above normal temperatures are forecast for “at least into the first part of July” and he added it’s likely the entire summer will be hotter than normal.