Nature Notes: Is damp cold colder than dry cold?
Published 5:30 pm Friday, December 30, 2022
By Akiko Nakagawa
In my family (and in the office here at the Nature Center) most of us generally agree that damp cold is worse than dry cold. Because of how unanimous this opinion is, I had naively assumed that there must be some sort of scientific understanding as to why humid air during the winter time feels so much colder than dry air. Well, I was surprised to learn that there is in fact no clear scientific explanation for why we feel this way.
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When we talk about humidity in the air, we are actually talking about a ratio called relative humidity. Relative humidity is the amount of water vapor in the air in comparison to the maximum amount of water vapor the atmosphere could theoretically hold — it’s often expressed as a percentage. This is what we are referring to when we complain about high humidity in the summertime. Our bodies are masters of thermoregulation (that’s a fancy word for controlling our inner body temperature). When we are hot, we produce sweat in order to cool down. Our sweat evaporates from our skin, turning into water vapor and entering the atmosphere. With high humidity though, little to no additional water vapor can enter the atmosphere, which means our sweat can’t evaporate and help us cool down. That’s why on hot and muggy days, we actually do feel hotter, and there’s a scientific reason behind it.
So, what happens when it’s cooler? When the temperature is around 50 degrees, we do tend to feel colder when it is humid compared to when it is dry. This is because the extra moisture in the air comes into contact with our skin and clothes. That moisture then evaporates using some of our body heat as energy, enhancing heat loss. So then why doesn’t this explanation add up when it’s colder out? When temperatures fall below freezing, the maximum amount of water that the atmosphere can hold is minuscule to begin with. That means there isn’t actually a significant difference in the amount of water vapor in the air on a ‘damp’ vs a ‘dry’ winter day. A winter day is just plain dry regardless of the relative humidity.
If that’s the case, you may be wondering why some people insist that it feels colder on a damp winter day than on a dry day. There isn’t much research to back up either claim, and the difficulty in studying this topic comes from the fact that ‘feeling cold’ is very subjective. There are a couple less scientific explanations nonetheless: No. 1, we simply associate damp days with clouds and precipitation, and the sun is warm (think about how a cloudy, snowy 20 degree day feels much colder than a sunny one) and No. 2, we associate damp weather with slush and warmer temperatures, and therefore dress less appropriately for the weather. Ditching our windproof winter coats and extra gear like scarves, gloves, and hats makes us less prepared for the cold, making us feel colder, when we’ve actually brought the coldness upon ourselves.
I hope everyone had a lovely holiday season and is staying warm as the cold (damp and dry alike) continues to persist through our Minnesota winter.
January at the Nature Center
Jan. 1, 2, 16: Interpretive Center Closed
Jan. 18: Free Live Bird Program
Jan. 28: Friends Members only: Free Cross Country Ski Lessons 8:30-10:30 a.m.
Jan. 28: Friends Annual Meeting 1:30-3:30 p.m., Ruby Rupner Auditorium