(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 (37.8 degrees Celsius) 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 (42.1 degrees Celsius) and Dengfeng hit 106.9 degrees (41.6 degrees Celsius) 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 (38.9 degrees Celsius) 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 (17.8 degrees Celsius) to 105 (40.6 degrees Celsius) in just nine hours Wednesday. Then on Thursday the temperature peaked at 104 (40 degrees Celsius), 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.