More on Temperature Adjustments

With what facts / justification / data is the GISS reducing measuremet temperatures prior to the 1970’s?  Climate Audit has more.  Whatever the justification, the adjustments are increasing station temperatures by as much as 3C, a signal correction that is far in excess of the signal (0.6 degrees C or so of warming).

More on adjustments here and signal to noise ratio in temperature measurement here.