The heat wave currently baking the midsection of the country has turned portions of at least 21 states into a sauna, with unusually high humidity with air temperatures running up to 20 degrees Fahrenheit above average.
On Wednesday, as high temperatures reached the mid-90s all the way into southern Canada, dew points that exceeded an astonishing 80 degrees Fahrenheit sent the heat index which measures how hot it feels to the human body soaring into the 100s.
On Thursday, similar conditions are predicted for much of the corn belt, where evapotranspiration from corn fields is boosting the amount of moisture in the air. This phenomenon, known as “corn sweat,” is helping to make the heat more unbearable in states like Iowa and Minnesota, in particular.
The high humidity with this heat wave reflects recent trends that have taken place as the climate warms in response to the buildup of greenhouse gases in the atmosphere.
It is also a preview of what is likely to be a normal summer hot spell for many parts of the U.S. within the next two to three decades.
At DSM, the total number of hrs (since 1973) w/Heat Index greater than 110F is 127. We’re expecting to add roughly 10 more today & tomorrow.
NWS Des Moines (@NWSDesMoines) July 20, 2016
In short, global warming is leading to more humid heat waves, which raises the danger to public health. Heat is already the top weather-related killer in the country.
Here’s how meteorologist Paul Douglas described the heat and humidity in Minnesota for the Minneapolis Star Tribune:
“Think of it as a free sauna, without the towels and cucumber-infused water samples,” he wrote.
The heat will move around the country through next week, centered in the Central U.S. on Thursday, then bringing the blowtorch heat and humidity to the East Coast during the weekend, followed by a shift of the heat dome to the Southwest for next week.
For example, in St. Louis, the National Weather Service is forecasting a maximum heat index on Sunday of 113 degrees Fahrenheit, or 45 degrees Celsius.
In Washington, D.C., the air temperature may hit 100 degrees Fahrenheit or higher during the weekend, with the possibility of a long duration heat wave, which would increase the risk of heat-related illnesses. If the air temperature does hit the century mark, it would be the first time this has happened there since 2012.
By Tuesday and Wednesday next week, such extreme heat indices will be confined to the Southeast and Southwest regions, as a series of cold fronts zips along the northern tier of the country, triggering rounds of severe thunderstorms.
The culprit for the sultry weather is an unusually intense and expansive area of high pressure, also referred to as a “heat dome,” that is currently parked over the Central U.S.
The clockwise circulation of air around this high is dragging moisture from the Gulf of Mexico and pumping it northward, all the way to Canada, which is also contributing to the high humidity levels.
Hot summers becoming the norm
With few exceptions, scientists have found that extreme, long-lasting heat waves that come with high humidity are a hallmark of global warming.
As average temperatures increase around the world, there is a higher probability of extreme heat events, and this has already been observed in the U.S. and other countries.
In fact, analyses that have looked at the influence of global warming on specific extreme events in the U.S. and abroad (research that is known as “attribution studies”) have nearly unanimously found that global warming made such heat waves more intense, more likely to occur, or both.
For example, studies published in 2014 found that manmade global warming is causing up to a tenfold increase in the risk for prolonged and severe heat waves.
Studies tied global warming to 2013 heat waves in Korea, Japan, Australia, Europe and China, among other areas.
Other studies have attributed the deadly 2003 European heat wave, in which at least 40,000 people are thought to have perished, in part to global warming.
While such post-mortem investigations are important for advancing our knowledge of the consequences of climate change, studies showing what’s in store for our near-term future are perhaps even more informative.
They are also sweat inducing.
Heat waves today will soon be the normal summer climate
A heat wave like this one today is likely to be viewed as typical summer conditions by just two decades from now, studies show.
One study, which was published in 2015 in the journal Nature Climate Change, found that the probability of 1-in-1,000-day hot extremes over land is already about five times higher than it was in pre-industrial times, when global average surface temperatures were lower.
Another study, published in February in the journal Climatic Change, found that severe heat waves that typically occur once every 20 years could become annual events across the majority of the world’s land areas by 2075, depending on greenhouse gas emissions from burning fossil fuels.
The climate research and journalism group Climate Central has documented the likely increase in so-called “danger days” when heat indices reach or exceed 105 degrees Fahrenheit, or 40 degrees Celsius.
Washington, D.C. averaged just 10 such days per summer in the year 2000, but climate projections show this could increase to 31 days in 2030, and then to a staggering 49 days by 2050.
Essentially, Climate Central says, the climate of southern Texas is migrating to Washington, D.C., due to human-caused global warming.