'Corn sweat' heat domes are becoming more common due to global warming

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. 

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.

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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