Longer exposure to less intense cold (e.g., 16°C for six hours) can increase norepinephrine.

“Whereas, other studies have shown that if people go outside in 16 degree Celsius weather with a proper amount, but a fairly minimum amount of clothing, you can experience even greater increases in norepinephrine. But the time that's required in order to experience those increases is six hours at, for instance, 16 degrees Celsius.”