Possible Clues:

• Presumably, The Weather Girls recorded them with The Three Degrees and others
• Pear tree must develop in various degrees of heat
• Degrees of difference between the seasons?
• They're taken in the medical profession as indicators of those in 1 down, for instance
• The Sisters of Mercy have been known to take them as The Weather Girls record them
• Degrees of warmth are returning in half-cut tree stump
• The nurses take them from the Met office
• Different degrees of heat
• Ranges of heat