Besides the research discussed in the other comments we have now many documented cases of people falling into extremely cold water in the winter, being pulled o

Besides the research discussed in the other comments we have now many documented cases of people falling into extremely cold water in the winter, being pulled out after an hour, and recovering. The warming has to be done properly though, if you just pull them out and heat them up immediately they'll die. If you just pull them out and let them warm up very slowly in a warm room they'll die. You have to heat them up as evenly as you can at a certain rate. When you consider that oxygen deprivation is the primary cause of cell death it makes sense. Cooling down the cells greatly reduces their metabolism and thus oxygen requirements. But cooling the heart down before the brain just makes the brain run out of oxygen first. The more oxygen-dependent the organ the more critical it is that organ be cooled first. Conversely you can't warm up those organs before the heart and lungs or they'll survive that long time of cooling only to die during warming due to lack of oxygen.