If it is zero degrees out today, and twice as cold tomorrow, how cold will it be tomorrow?

There's really no such thing as twice as cold since the scale of temperature is arbitrary. If you establish two values, you can talk about what change lies between them. For instance:

today the high was 50 degrees F. Yesterday the high was 20 degrees F. Tomorrow's high is forecast to increase 100% of the increase between yesterday's high and today's high-- or, to 80 degrees F. But to say, it will be 100% hotter or colder tomorrow than it was today is meaningless since the numbers we designate as values of temperature are merely numbers--not really mathematical expressions. Zero degrees F is just a name for a value we've agreed shall represent the change between one arbitrary measurement and another. It's not bound by the same rules as a mathematical zero.

Substitute 100 degrees for zero and you still have a nonsensical question.

Word puzzle. It will still be zero degrees. 2 x 0 = 0

0 degrees because you can't double zero

Twice as cold.

0 degrees. 0 multiplied by any number is still zero.

-2

If this is Celsius, 0 C = 273K.

Half of that is 136.5K, or -136.5 C

For Fahrenheit, it'd be about -230F

-25C.

Ambient temperature is supposed to be 25C, so, I assume twice colder than that would be -25C.

like -1 or something