Temperature unit conversion does not work for temperature intervals

Problem Statement
"We wish to limit global temperature rise to 4 degrees Celsius."
The above cannot be converted in calculator to
"We wish to limit global temperature rise to 7.2 degrees Fahrenheit."

Evidence or User Insights
It is acceptable usage to talk about temperature intervals in degrees Celsius and degrees Fahrenheit, and it should be possible to use temperature intervals rather than a specific temperature on the Celsius or Fahrenheit scales. Failure to make this available will have our poor American colleagues misunderstanding that we are not talking about limiting global temperature rise to 39.2 degrees Fahrenheit!

Proposal
Either:
a) Where there is currently a single option for "Temperature" in the hamburger, have two: Temperature (Interval) or Temperature (Scale).
b) Keep the single option for "Temperature" in the hamburger, then have a separate radio button along the lines of "Interval (referring to the difference between two temperatures)" and "Scale (referring to what temperature an object is)"

My preference would be b).

Goals
Stop people incorrectly converting units when they are talking about a temperature interval.

Non-Goals
We are not submitting a bug to upstream governments to ban the use of Celsius and Fahrenheit. While we would all eventually get used to saying "it's 270 Kelvin out!", it is more common to know when you are talking about a scale and when you are talking about an interval.

Start by reproducing the Celsius-to-Fahrenheit conversion for a temperature interval in Calculator, then inspect the temperature conversion UI and related conversion logic. The issue provides no file or test names, so trace the existing Temperature option before choosing between separate interval and scale controls. Done means interval values convert correctly without changing ordinary temperature-scale conversions.