davidstarlingm wrote:Radiative cooling will take several hours at minimum before your temperature will drop more than a degree or two, IIRC.
Using the calculator on this site
, a naked human with 2 square meters of skin radiating as a black-body at a temperature of 34 Celsius against a background of 3K radiates at around 1kW - so, treating the human body as mostly water, with a specific heat capacity of around 4 kJ/K/kg, and a typical body mass of around 60kg, it would take about 4 minutes to lose enough heat energy to reduce the average body temperature by 1K - call it 5 minutes to account for rounding errors.
Of course, that's ignoring the body's natural heat production - spot research turns up a basal metabolic rate of 90W, which can be supplemented by additional heat generation, but on its own is enough to make it "about 5 minutes" rather than "less than 5 minutes". To get it up to an hour, you'd need to be producing over 90% of the heat being radiated (call it 900W or ten times the basic rate).
Of course, the other factor is the body's ability to conserve core heat at the expense of extremities, which I'm not even going to guess at.