Sweat Stains for Science

There are those, unnamed, who retain their skepticism as to our planet's warming, or at best claim humans have nothing to do with it. I don't have a ready answer, other than to point out the phenomenon's frequent mention by scientists. Data is data.

James Janega has more:

Chicago Tribune news : Sweaty? Blame global warming. If you are feeling stickier this summer, scientists can explain:


When it comes to global warming, climatologists say, it's not just the heat, it's the humidity.

Despite widely varied regional differences -- drought here, torrents there -- the world as measured by average dew points has dampened, for the simple reason that warmer air has the capacity to store more water vapor.

That includes the Midwest, where summers have been getting muggier, just slightly, but enough for us to feel a difference.

In the 1960s, Chicago's mean summer dew point, the temperature at which water condenses from the air, was 58.9 degrees Fahrenheit. It has increased 1.5 degrees since then, and has hovered the last 10 years around 60.4 degrees.


As a general summer guideline, meteorologists at AccuWeather say dew points below 60 degrees Fahrenheit are comfortable. We start to notice humidity at dew points between 60 and 64 degrees, about where it will be Saturday in Chicago.
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With dew points somewhere in the 60s, the atmosphere loses the capacity to absorb sweat as fast as we can produce it, say meteorologists with the National Weather Service.

“When [dew points] start getting up into the 70s, that's when it gets really miserable out there,” said Illinois state climatologist Jim Angel of the Illinois State Water Survey.

Because heat and humidity are so closely related, it was one of the first places looked at when climatologists at the National Center for Atmospheric Research, or NCAR, in Colorado sought evidence of global warming. They used satellites to monitor patches of warm, damp air for signs they were expanding.

“If there's global warming, you almost have to find it,” NCAR project scientist John Fasullo said, referring to expanding humidity. “We found it.”

In time lapse images, water vapor over hot equatorial seas expands from the Earth's middle, advancing over the last 30 years into what once were more moderate climates.

Recent research has found water vapor increasing around the world -- about 4 percent more than 30 years ago -- a byproduct of global oceans warming by 1 degree Fahrenheit, explained climatologist Kevin Trenberth, who has co-authored research with Fasullo.
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A look at weather records resulted in a string of papers. One showed 40 years of rising dew points at O'Hare International Airport, another went back still further at Midway Airport, and a third found 50 years of increasing dew points from St. Louis to South Bend, Ind.

“We basically found out we've had a lot more frequent high dew point days and hours in the last 20 years or so, since the 1980s, than we did in the period before that,” Changnon said.

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