How cold does it have to be to get hypothermia?

My boyfriend for some reason wants me to move to Sweden.

I told him that I refuse to live anywhere where you’d die if you forgot your keys and had to spend the night outside.

He claims that that’d happen right here in sunny Santa Cruz! I’ll admit it gets pretty damn cold here- but for us Californians, pretty damn cold is a low of thirty degrees. It sometimes dips into the twenties, but that is pretty rare.

So, if I lost me keys and had to spend the night outside in a tee-shirt and a pair of jeans, in twenty to thirty degree weather, would I die?

Hypothermia is caused by a decrease in your core body temperature. Lots of things affect how cold it has to be for you to start exhibiting symptoms, including how big you are, how much fat you have, what your metabolism is like, blood circulation problems, other medical conditions, and so on. A night spent exposed to the elements in thirty degree weather would probably not kill a relatively healthy person, but he would probably start exhibiting some symtoms of mild hypothermia including shivering, blue appendages, diminished mental capacity, poor coordination and slow heart rate.

The quickest way to get serious hypothermia is getting wet. If it’s raining or you fall in a lake you are in a lot more trouble.

While I’m not sure about “lethal” air temps, I do know that cold water is definately very bad. When I was on the west coast (Canada) fishing on the sea, we were about 200 yards from the shore of an island and talking about what would happen if the boat capsized. I thought I could at least akwardley make it to shore since I had a life jacket on. The guide said I’d freeze to death before I could make it; and I had figured it would take me less than 15 minutes to get to shore. This was in the winter with water temperatures in the 5-10C range.

No way this is true. In fact, I wouldn’t be surprised to find out that I had spent the night outdoors somewhere in Santa Cruz. Not surprised at all.

More seriously, taking a low of 50° (about right for San Francisco and Santa Cruz, no?), I can say from experience that sitting for up to 4 hours after dark falls far short of causing hypothermia. Witness night games at Candlestick Park, or Friday nights on the Stevenson Knoll. :wink: Take a walk or two, that’ll keep the blood warm and moving.

If I am not mistaken you can get hypothermia by staying in the ocean with the water at 80 degrees or so. As long as it is enough to lower your body temperature below the critical temp, which I don’t know, you can get hypothermia from warm water.

Table one on this page gives estimates on the time to feel the effects of hypothermia in water.

The most common temps to get hypotheremia is something around 60. People aren’t expecting to get very cold in those temps, so they don’t worry so much about getting wet, cold, and eventually hypothermic.

Getting wet will accelerate the process. I mainly deal with hiking, and it’s pretty common for people to go into the first stages of hypothermia (shaking, shivering, losing the ability to think straight) in rainy conditions at temps of 50-60. The exersion of hiking certainly pushes the onset. You often have to work hard to convince people to put on warm clothes, they don’t realize what it going on.

Don’t forget your keys.:wink:

Seriously, I wouldn’t worry so much about hypothermia as much as just plain not liking cold weather.

I live in an area that has snow on the ground a good 6 months out of the year. We got around 20" the first week of October. It takes a bit of adjustment for just about anybody. Some people can take it, some can’t.

Any amount of clothing will help prevent hypothermia, but the average naked adult can indefinitely withstand temperatures in air down to about 2ºC (34ºF) so long as they stay dry, and provided they have a source of food energy (or fat stores) to generate body heat. Water conducts heat away from the body much more readily than air, so a water temperature of 20ºC (68ºF) will kill eventually.

This does not apply to children, who are much more susceptible to hypothermia than adults.

Math error alert: There is no temperature which could be expressed as both 2ºC and 34ºF, using any consistent rounding scheme. 2ºC is at least 35ºF, and probably 36.

But the point stands: Temperature isn’t as important as other factors.