Godfrey Dack writes in with this:
Everyone will be familiar with the difficulty of listening to a conversation held with a friend in a crowded room with many other conversations going on at the same time. So it is with many fields of scientific investigation where it is difficult to tease a particular trend out from masses of data. In the first case, we could call the friend’s conversation ‘The Signal’, and the background conversations ‘The Noise’.
In looking at climate data, trends (the signal) can be graphically represented by a (generally) smooth curve, usually flanked by a range of experimentally predicted or actually measured values (the noise). Joining up every point on a graph of such data would give a jagged line which could be thought of as a combination of many alternating functions over a wide range of frequencies.
If you tuned an old-fashioned analogue radio away from any station the hiss you would hear would be termed ‘White Noise’ whose frequency distribution would be random but whose intensity would be equal over all frequencies like the spectrum of pure white light. Another type of noise encountered in nature shows a random distribution of frequencies but each frequency octave carries the same amount of energy and, because energy of a wave is inversely proportional to the frequency, to make all ‘octave containers’ have the same energy, low frequency octaves carry a greater proportion of the overall energy and because, in light, low frequencies are at the red end of the spectrum this noise is called ‘Pink Noise’. Pink noise phenomena occur a lot in nature and can be the result of some low frequency (i.e. long time-period) disturbance.
In a recently published paper with the snappy title – ‘Intrinsic Pink-Noise Multidecadal Global Climate Dynamics Mode ‘ (paywalled) the authors claim to have discovered pink noise energy signatures, on time scales over many decades, appearing in historical climate proxy data both before, and after The Industrial Revolution. The authors looked at two large data sets: monthly average surface temperatures from 1901 – 2012, and radiological ice-core measurements dating back many thousands of years.
The ‘pink-noise’ aspect of the analysis suggests that there may be some aspect of climate variation due to a naturally produced slow varying function which may be acting together with anthropogenic factors in a resonant fashion rather like an adult pushing a child on a swing just at the right moment can rapidly increase the amplitude of the swing.
The authors make no attempt to identify the origin of the suspected natural component, be it solar, astronomical or as yet of an unsuspected nature, however, if such natural forcing does exist on top of man-made forcing, it may exaggerate the significance of anthropomorphic factors in climate change.