I'm dreaming of a white Christmas

That's one of the ways proposed for terraforming Venus. Put in a sun shield to freeze the planet, let the CO2 snow down, then process the CO2 into something that can sequester it away so it doesn't just go back into the atmosphere after removing the sun shield.

Of course none of that is technically possible right now, but it's a lot easier on a planet that has no (known) life to destroy while working through the process.

mmm, delicious carbonjack

For the most part, it varies by material and state of matter, but assuming the chemical composition doesnt change and no material changes phase, then it is pretty close to linear in most materials.

Fun fact: gas pressure changes linearly with temperature. If you make one of these plots at mild conditions you can extrapolate the line down to zero pressure and measure where absolute zero temperature is

Half Kelvins?

0 is the freezing point of water 50 is the boiling point.

If it's 30°c outside, it will be only be 15 after the wish, thus fit what the character said

But it's not.

Celsius and Faernheit are interval scales, not rational scales. The absolute change from one number to the next is consistent, but since you can go into the negatives, 1 is not double 2.

Kelvin and Rankine are rational because they use an absolute zero.

to make the argument even simpler, that phrase wouldn't even mean the same thing to an english person as it would to an american.

In fahrenheit those temps would convert to 95f and 158f.

If you convert those temperatures to Kelvin, they become 308K and 343K. Since Kelvin is absolute and we're measuring the same material, this tells you how much more thermal energy is there and their actual proportion to each other.

308.15K is not half of 343.15K

For a present, I think it would be fun to have a contract lawyer draft up an ironclad 3 wishes contract