"In meditative states, the monks had remarkable control over their body temperature and oxygen intake. They could use their body heat to dry wet towels placed around them, where most people would shiver uncontrollably. They could raise the temperature of their fingers and toes by as much as 17 degrees. Some could even spend a night on a rocky ledge at an elevation of 15,000 feet in the Himalayas, where temperatures f…
It is 17 degrees Fahrenheit, and the study mentions 8.3 degrees Celsius. A linked follow up study in 2013 was able to reproduce temperature increases between 1 and 6 degrees Celsius [2] Also, the results suggest that "...the peripheral temperature increases are primarily the result of increased peripheral blood flow due to peripheral muscular action (and proximity of the femoral artery) rather than a result of psychological (caused by meditation) or physiological (caused by breathing or isometric techniques) states." It looks like it is caused by blood vessels opening up (vasodilation) as a response to certain kinds of breathing exercises. If true, it is just an indirect result of the practice, not some form of body control that extends to other use cases.
[1] https://www.snopes.com/fact-check/harvard-study-confirms-tib... [2] https://journals.plos.org/plosone/article?id=10.1371/journal...