What makes us feel cold?
As a senior in high school, Mark Ewens and his friends ventured out into a rare New Orleans snowstorm.
Standing on the edge of Lake Pontchartrain, they let a 40- to 45-mph wind blast the barely freezing air across their faces.
"And, of course, to us that was just unbelievably cold," Ewens said.
Jump ahead 35 years, and it doesn't seem so cold anymore to Ewens, a technician at the National Weather Service in Grand Forks, N.D.
Not compared with delivering newspapers at 40 below zero - with the flu.
And certainly not compared with his military days in Alaska, when the temperature plummeted to 70 below zero.
Still, Ewens said the debate never ends - including in his office - over what constitutes cold and what makes us cold.
And the answer seems to be: It depends on whom you ask, and where you ask them.
"There are people who have just a much greater tolerance to cold," he said.
Many factors to cold
The number on the thermometer isn't a very good indicator of how cold we feel, said WDAY-TV meteorologist John Wheeler.
Wind, humidity, sunshine, clothing, activity, exposure time and an individual's physical makeup are all contributing factors.
"Sometimes we forecasters get a little hung up on the high and the low, and it's not the whole story," he said.
The National Weather Service takes into account that residents of some regions are better suited for the cold than in other areas.
For example, the Grand Forks office issues a wind chill advisory when the wind chill is 25 to 40 below zero with a wind speed of 10 mph or greater, and a warning when it's less than 40 below with a 10 mph wind or greater. But in Memphis, Tenn., the criteria is zero degrees for an advisory and 18 below for a warning.
High relative humidity also can intensify the chill in cold weather, because it increases the conduction of heat away from the body. But when the temperature drops below 32 degrees, humidity doesn't mean much, Wheeler said.
"There's not enough moisture in the air to chill you down," he said.
Charles Snell, a 24-year-old general construction laborer, was working Wednesday morning on the Cityscapes project in downtown Fargo in 24-degree air with 88 percent humidity - preferable to the subzero conditions he'll likely endure in January, he said.
"The worst kind of weather would probably be a lot of wind when it's cold," he said.
Sunshine also makes a big difference in how cold a person feels, Wheeler said. According to the weather service, sunshine can increase the wind chill temperature by 10 to 18 degrees.
But no matter how many external factors are considered, it often comes back to the individual's physiology, Wheeler said. For instance, he said he and his wife have shared a dual-control electric blanket for many years.
"And she usually sets her side on 'blast,' and I've never turned mine on," he said.
Protein behind chill
So, what triggers that cold sensation in the human body?
David McKemy and fellow researchers at the University of Southern California tackled that question in 2002.
They proceeded under the notion that whatever it is in the body that reacts to menthol with a "cool" sensation may be related to the chills people feel in cool or cold weather, McKemy said.
The answer: TRPM8, a protein found in the cell membrane of a neuron.
The protein, known as an "ion channel," allows calcium and sodium ions to pass through the neuron's cell wall, which triggers an electrical impulse that travels through the spinal cord to the brain, resulting in the perception of cold, McKemy said.
"Menthol activates this protein, and also cold activates this protein, too," he said. "And so the reason why mint and menthol feels cool is it's essentially tricking this protein into thinking it's cold."
A follow-up study attempted to locate the nerves in the body that produce the protein - including whether they're to blame for the tooth pain that some people feel when biting into ice cream.
The study found that the protein-producing neurons are located throughout the body - "every place you can think of that you can feel temperature," McKemy said.
"There are these little nerve endings that are sticking into the epidermis of the skin, and this is where this protein is located, and this is where it's actually sensing changes in temperature on the outside of the body," he said.
As for whether the protein may be more prominent in some people than others, McKemy said scientists haven't looked at that yet, and doing so would quickly become very complicated for a variety of reasons.
One reason, he said, is that people adapt very quickly to temperature changes.
"The nerves themselves that detect cold will kind of adapt to that a little bit," he said. "They decrease their activity, because you don't want to always be sending that cold signal."
Since settling in Grand Forks almost 30 years ago, Ewens said he has become so acclimated to the cold northern clime, he can barely tolerate the heat and humidity when visiting his hometown during the summer.
"It's miserable," he said.