Not to be a stickler (ok I like being a stickler) but temperature delta, especially deltas between degrees celsius, should be given in kelvin. A 1.8K difference makes sense. A 1.8C difference would be 274.8 kelvin!
There is no difference in the amount of energy 1 degree Celsius delta and 1 degree Kelvin delta represents.
The only (and I really mean only) difference is how zero energy is defined. It is not possible to have negative energy, and that zero Celsius represents the freezing point of water is an artifact of convenience, not of absolute definition.
Ratios are undefined because the Celsius scale has no absolute zero while the Kelvin scale has.
Categorically and factually incorrect.
A 1.8 degree C different would be 1.8 kelvin. The two degrees have different zero points but one degree Celsius and one degree Kelvin are identical in magnitude.
I think there was some insight here that went off on a bad tangent leading to a math word-problem mistake, confusing these two:
1. A difference... between [X] and [Y], which is a delta of 1.8°C
2. A difference... between [0°K] and a reading of [1.8°C], which is a delta 274.95°K.
Most people do not understand temperature on the Kelvin scale. As such, you should not use it to communicate in a general setting such as this.
"An absolute difference of 1.8C, or 274.8K, measured between A and B"
or
"A relative difference of 1.8C, or 1.8K, is added/subtracted to A/B in order to reach B/A"
I don't think the context-free variant with K will improve understanding and decrease confusability in this discussion context, but I appreciate the pointer about it in general. I'll take a lot more care around it in a future thread about space apparel!
A relative difference[2], usually given in percent change, has problems with a unit that has an offset zero like Celcius, but that isn't what anybody is using here. It's more than simple subtraction; you have to divide by the reference value.
[1] https://en.wikipedia.org/wiki/Absolute_difference#Applicatio... [2] https://en.wikipedia.org/wiki/Relative_difference
See, a degree is not an absolute unit of measure like a Celsius or a Kelvin, it's a relative difference between two absolute units of measure. When discussing the difference between two separate temperature readings measured in Celsius, degrees Celsius is entirely appropriate.
Think of it like time: there is a difference between meeting at 2:00 and meeting two hours from now.