Temperature anomalies are not additive. The temperature on Earth varies from -89C(184K) to 56C(330K). The power required to maintain those temperatures are 65w/m^2 and 670W/m^2 respectively.
Temperature anomalies are the change in temperature from some baseline period. To maintain +1C in an area where 0C is the norm requires the addition of 4.6W/m^2. Where the mean is 20C, 5.6W/m^2 is needed to sustain +1C.
Temperatures should be converted to watts per meter squared prior to computations for climatology.