Why must Kelvin temperatures be used in calculations that involve gases?
The gas laws are based on absolute temperatures. Kelvin is an absolute temperature scale. Besides that, absolute zero is unattainable, so one can never run into the issue of dividing by zero (unlike in the celsius scale).
0 degrees Kelvin is 0 absolute zero. When the absolute temperature of the gas in Kelvin degrees is doubled the kinetic energy of the gas is doubled. It is critical to the gas law calculations that there be a direct relationship between the temperature and the kinetic energy.
No other temperature scale is based on absolute zero and temperature. Other temperature scales like Centigrade must be converted to Kelvin for the gas laws to work.