Signal to Noise Ratio, Part 2

Anthony Watts and Steven McIntyre make an interesting observation, using an example temperature measurement point in the US and Global Historical Climate Network (the network that most historic global warming estimates are made from).

Over time, temperature measurement points, even those nominally in the same town, tend to change.  The measurement technology changes (from bulbs to electronics) the location can move across town, and towns with their heat islands can encroach.  As a result, scientists try to make guesstimate corrections to the historical data to take these events into account. 

Taking just one example measurement point, at Petaluma CA, Watts and McIntyre show how two different adjustment approaches by scientists at this location change the historic warming measured by over 1.5 degrees C.  Note that this "noise" is more than twice the value of the estimated "signal" -- the estimated 0.6 degrees C global warming over the last century.

More on signal to noise ratios in global warming measurement.