If we were in the middle of a spell of cold weather, President Donald Trump would be racing to Twitter to fire off a tirade about how the world could really use some global warming .

But as a potentially deadly and record-setting heat wave grips the country the type of event that Trumps own government scientists recently warned will become more frequent and severe due to human-caused climate change its unlikely hell have much to say.

More than half of the mainland United States, from the Rocky Mountains to the East Coast, has been engulfed by extreme temperatures and high humidity since early this week. The National Weather Service on Thursday said the widespread and dangerous heat wave will persist into the weekend. The heat index, a measurement of how hot it feels when accounting for humidity, is expected to soar to 110 degrees Fahrenheit in cities like New York, Washington, Detroit, St. Louis and Philadelphia.

As of Thursday, 154 million Americans were under heat advisories or warnings , according to The Washington Post. And many people in the heat waves path can expect little relief at night, as the urban heat island effect will prevent major urban centers from cooling off after the sun goes down. More than 120 record warm overnight low temperatures will likely be tied or broken, according to the Weather Service.

Extreme heat is a leading cause of weather-related deaths in the United States, resulting in an average 658 fatalities each year , according to the Centers for Disease Control and Prevention. Thousands more suffer from heat-related illnesses, including heat exhaustion and stroke. The elderly, children, poor people and people who have manual labor jobs outdoors are among the most vulnerable during heat waves.

On Tuesday, as sweltering heat began to take hold of the central and eastern U.S., the Union of Concerned Scientists published a report saying that without swift action to rein in greenhouse gas emissions, the number of days per year in the U.S. when the heat index exceeds 100 degrees could more than double by 2050 and quadruple by the end of the century.

Our analysis shows a hotter future thats hard to imagine today, Kristina Dahl, a senior climate scientist at UCS and a co-author of the report, said in a statement. Nearly everywhere, people will experience more days of dangerous heat even in the next few decades.