Today the temperature is 20 degrees Celcius, and 2 weeks later it is expected to be two times warmer; around 40 degrees Celcius.
WRONG!
A temp 2 times warmer than 20 deg Celcius is actually
(273 + 20) x 2 - 273 = 586 - 273 = 313 deg C
A temp 2 times warmer than 0 deg Celcius is actually
(273 + 0) x 2 - 273 = 273 deg Celcius.
Explanation.
Temp should actually be measured from absolute zero and is properly expressed in degrees Kelvin. The approximate freezing point of water is 273 deg Kelvin. We use a couple of scales, Farenheit and Celcius, to help keep numbers sensible within our daily experince of the world around us. They should not be confused with proper measurement of absolute values of energy.
Cheers,
TheOddOne