If it's zero degrees outside today and it's supposed to be twice as cold tomorrow, how cold is it going to be?

It's anybody's guess. "Twice as cold" is a meaningless phrase.
No reliable weatherman would ever forecast it.

"Cold" is not a thing, and it can't be measured.  "Cold" is just a
lack of heat, and it feels different to different people.

Here are some other things that can't be measured, for the same reason:

-- darkness  (lack of light)
-- quietness  (lack of sound)
-- loneliness  (lack of companionship)
-- poorness, poverty  (lack of resources) 
-- vacuum  (lack of pressure)

There are no units of measure for lack of something.
The only way to measure these things is to measure how much
light, sound, heat etc. there IS.  Then, if that seems low to you,
you'll say that it's dark, quiet, or cold.