However, temperature anomalies are much better correlated over large distances, and this is why the global
mean temperature calculations use local anomalies not absolute temperatures.
It seems to me that a good outcome of Paris this year would be an agreement to set out a network of sensors that can reduce the noise in the annual global
temperature calculation by a factor of 3 for at least three decades.
I have done complex modelling and you never get usable solutions if your uncertainty of your coefficients and conditions is as big as those feedback effects (that why we have large deviations between models and real life year - to -
year temperature calculations).
But because the emission wavelengths change
with temperature the calculation of εa (Ta) is the measured value of εa at each wavelength weighted by the Planck function at Ta.
Omission of successively larger polar regions from the global -
mean temperature calculations, in both tropospheric and surface data sets, shows that data gaps at high latitudes can not explain the observed differences between the hiatus and the pre-hiatus period....
The response of GISS was to say «it doesn't matter, since the USA is only 2 % of the total area of the world and this small error has no effect on the global
average temperature calculations».
The Intergovernmental Panel on Climate Change, the body of climate scientists that was formed to provide assessments to the United Nations, bases
its temperature calculations on an 1850 - 1900 global average.
Further,
the temperature calculations are independently confirmed by four different sets of weather balloons that measure atmospheric temperatures using thermometers.
The full 2015 surface temperature data set and the complete methodology used to make
the temperature calculation are available at data.giss.nasa.gov / gistemp /.