10 °C = 50 °F (temperature)
10 °C = 18 °F (temperature difference)
Celsius and Fahrenheit date to before temperature was understood to have a lower limit. Both measure only temperature difference from their respective zero points, with the conversion to energetic temperature demanding that one knows where the zero points are. The conversion is implicit in common use, so that
10 °C + 10 °C = 273.15 K + 10 °C + 10 °C = 273.15 K + 20 °C = 20 °C
And thus 32 °F = 16 °F, which, with conventional mathematics, can only be satisfied if °F = 0. Express this in English as "Fahrenheit is nothing", which is something that every European already knows. That's why we use Celsius :P
