The weather this past week has been a headline grabber. Tropical Storm Hilary drenched parts of Southern California. In fact, Death Valley received a year’s worth of rainfall in one day. In the Atlantic, a parade of named and unnamed tropical systems dot the landscape as we approach the peak of hurricane season. However, the most deadly weather threat this week is one that often does not garner headlines or prompt live reports on the scene—oppressive heat. Here’s what you need to know and how this current event compares to the oft-mentioned 1930s.
The National Weather Service is pretty clear about the threat this week, so its words are appropriate here. In the latest Weather Prediction Center discussion, NWS meteorologists write, “Over 100 million people under heat alerts from the Midwest to the Gulf Coast as record-breaking temperatures continue through the end of the week.” Temperatures will hover around the 100 degree Fahrenheit mark and in many cases exceed that mark. To make matters worse, the heat index values are a better indicator of what it “feels” like when humidity is considered. The discussion goes on to say, “When factoring in brutal humidity levels, maximum heat indices could approach 120 degrees … it is not uncommon for August to feature dangerous heat, these temperatures are extremely anomalous and likely to break numerous daily and potentially monthly records.” Some temperatures could be 20 degrees above average August values.
As jaw dropping as these potential daily maximum temperatures are, the elevated temperatures overnight are particularly dangerous from a health standpoint. This heatwave features overnight minimum temperatures near 80 degrees Fahrenheit. Vulnerable communities and people without adequate cooling resources or hydration are in danger. NWS meteorologists ended the discussion with a fact that seems to escape many people: “Remember, heat is the number-one-weather-related cause of death in the United States.” At the time of writing, some type of heat alert (watches, advisories, or excessive heat warnings) has been issued for 22 states, from the upper Midwest to the Gulf Coast. Around 130 million people are affected. That’s roughly 40% of the country. So what’s causing this massive heatwave?
The answer is a persistent upper level ridge of high pressure. When high pressure is stagnant over a region, hot and dry conditions are typically expected under such heat domes. By the weekend, a cold front should bring relatively cooler temperatures and some relief, so hang in there.
Because of El Nino, peak summer heating and changing climate, this year has featured anomalous heatwaves across the Northern Hemisphere. In June, I told the Associated Press, “The onset of El Nino has implications for placing 2023 in the running for warmest year on record when combined with climate-warming background.” This prediction is looking pretty solid. In fact, I am now wondering by just how much it will shatter the previous warmest year.
Early attribution studies have hinted that our record July global temperatures were fueled by heatwaves with the “DNA” of climate change all in them. The World Weather Attribution used methods published in the peer-review literature to conclude, “Similar to previous studies we found that the heatwaves defined above are 2.5°C warmer in Southern Europe, 2°C warmer in North America and about 1°C in China in today’s climate than they would have been if it was not for human-induced climate change.”
Ironically, a 2023 study out today has more dire news for the U.S. Midwest. The research, published in Nature Communications, concludes that places like Paris or Chicago could experience heatwaves of magnitudes not even experienced yet. They use the 2021 U.S. Pacific Northwest as a contextual “black swan.” Studies have found that it was virtually impossible for that heatwave to exist without climate change.
When lead author Erich Fischer tweeted about the new study, my initial thought was, “Oh, boy, here come the ‘what about the Dust Bowl or 1930s?’ posts.” My colleagues Jeff Berardelli and Scott Duncan must have anticipated that, too. Both have effective posts on the social media platform X (formerly Twitter) to counter that oft-cited zombie theory—one that lives on even though scientists have long refuted it.