I would say in this example it’s the ratio that’s important. In the original poll, the popularity is 40:60, i.e. 2 people like him for every 3 people that dislike him.

So to double in popularity, he needs to have 4 people liking him for every 3 people that dislike him, making a ratio of 4:3, or in percentage terms, about 57.14% for and 42.86% against.

I would have thought that ‘twice as cold’, if it has any validity or meaning whatever, must refer to the effect on human comfort; if it takes twenty minutes for your fingers to get frostbite at temperature X, then ‘twice as cold as X’ would be the temperature at which frostbite occurs in half the time.