[mrsmith2211 (OP)]

A month ago, 48 felt cold. Now 28 seems great! Is there a scientific explanation?

[alancalverd]

F or C?

[paul cotter]

Or K?

[chris]

There are a few factors to consider here:

We tend to dress, eat, drink and behave differently in anticipation of different weather and temperature conditions. The body adjusts metabolic rate (which burns calories to yield heat) as temperatures rise and fall, we also eat more when we're cold, and when we anticipate feeling cold so we wear more layers.

The nervous system is also acutely sensitive to change, but not to absolutes or steady states so much; this is nicely exemplified by this simple experiment you can try for yourself: https://www.thenakedscientists.com/get-naked/experiments/strange-temperatures
 
So, in summary, you neurologically "get used" to a temperature quite quickly, and this is reinforced by underlying physiological and behavioural changes that enhance resilience.

[alancalverd]

....up to a point!

I recall an exchange on another forum where a woman asked how long it would take for her to acclimatise to having moved from Florida to Maine. One reply was "Never. Look in the shop windows - are they selling bikinis or fur coats?"