A major heat wave is currently sweeping across nearly half of the United States, bringing abnormally high temperatures and posing significant risks to millions of Americans. Experts have attributed the intensity and likelihood of this extreme heat to human-induced climate change, which has made Friday's scorching temperatures at least three times more probable, according to the Climate Shift Index by Climate Central.

The Climate Shift Index, launched in 2022, serves as a tool to measure and communicate the contribution of climate change to the magnitude of heatwaves. It revealed that a record-breaking 148 million Americans, approximately half of the country's population, are expected to endure excessive temperatures that have become significantly more likely due to climate change.

Shel Winkley, a meteorologist at Climate Central, described Friday's heat as an unprecedented climate change-driven event for the United States. Heat alerts have been issued for parts of 33 states, with an estimated 150 million people feeling the impact. The worst of the heat is projected to hit the South to the Mid-Atlantic regions, where heat indexes of 105 to 110, taking into account humidity, are anticipated. Certain areas in the West will also experience exceptionally high temperatures, with the added factor of lower humidity. Moreover, the scorching heat is expected to persist in these regions for an extended period.

The entire United States is forecasted to encounter above-normal temperatures, with some areas predicted to be 10 to 20 degrees higher than average. This comes after record-breaking heatwaves in the Upper Midwest and central Plains earlier this summer, as well as a sweltering July that affected both the United States and the global climate. In fact, July 2023 was the second hottest month on record worldwide, surpassed only by July 2022.

Examining data from Climate Central and other groups, such as the World Weather Attribution project, it is clear that the human-caused climate change has exacerbated the intensity of this summer's heat. The Climate Shift Index calculates the extent to which temperature deviations are influenced by climate change, with scores ranging from minus five to plus five. The current index indicates that temperatures made five times more likely due to climate change are concentrated along a large crescent spanning from British Columbia through the western United States and Mexico, extending across the Gulf Coast and up the East Coast into Atlantic Canada.

While the combination of heat and humidity will be most severe in the South to the Mid-Atlantic, the duration and magnitude of the heat are expected to be particularly notable in the western United States, particularly in the Pacific Northwest. These regions are already contending with severe drought conditions and large-scale wildfires. On Friday, Boise, Idaho is expected to hit a record high of 107 degrees, while Salt Lake City could approach its daily record of 101 degrees on Saturday. Phoenix is also bracing for record-threatening highs of 112 to 115 degrees, which may persist into early next week.

In the eastern United States, the D.C. area is under an excessive-heat warning, with temperatures nearing 100 degrees and potentially breaking records. Baltimore could experience its eighth day this year with temperatures reaching or surpassing 100 degrees. The increase in extremely warm nights has outpaced the rise in daytime temperatures in many locations, further exacerbating the overall heat.

While some relief is expected in parts of the northern United States as cold fronts move through, the high-pressure system known as a "heat dome" is likely to remain anchored over the Desert Southwest and parts of the South throughout at least the first third of August. A zone stretching from southwest Canada through the Intermountain West and into the south-central states could also remain significantly warmer than average for the next few weeks, with current projections favoring above-normal temperatures for much of August.

As this heat wave continues to grip the nation, it serves as a stark reminder of the urgent need to address climate change and its impacts. The increasing frequency and intensity of extreme weather events underscore the importance of global efforts to reduce greenhouse gas emissions and actively adapt to a changing climate.