By Basil Copeland and Anthony Watts, Watts Up With That

In Part I, we presented evidence of a noticable periodicity in globally averaged temperatures when filtered with Hodrick-Prescott smoothing.  Using a default value of lamda of 100, we saw a bidecadal pattern in the rate of change in the smoothed temperature series that appears closely related to 22 year Hale solar cycles.  There was also evidence of a longer climate cycle of ~66 years, or three Hale solar cycles, corresponding to slightly higher peaks of cycles 11 to 17 and 17 to 23. For the layman reader, this is much like a tunable bandpass filter used in radio communications, where lambda is the tuning knob used to determine the what band of frequencies are passed and which are excluded.

See larger image here

In part 2, a smaller lambda was used. A lower value of lambda would result in much less smoothing. To test the sensitivity of the findings reported in Part I, we refiltered with a lambda of 7. 

And when we look at the first differences of the less smoothed trend line, they too are no longer as smooth as in tghe graph above from Part I.  Nevertheless, the correlation to the 22 year Hale cycle peaks is still there, and we can now see the 11 year Schwabe cycle as well.

See larger image here

The pattern shown, while not as eye-catching, perhaps, as the pattern in first figure is still quite revealing.  There is a notable tendency for amplitude of the peak rate of change to alternate between even and odd numbered solar cycles, being higher with the odd numbered solar cycles, and lower in even numbered cycles. This is consistent with a known feature of the Hale cycle in which the 22 year cycle is composed of alternating 11 year phases, referred to as parallel and antiparallel phases, with transitions occurring near solar peaks. 

Even cycles lead to an open heliosphere where GCR reaches the earth more easily.  Mavromichalaki, et. al. (1997), and Orgutsov, et al. (2003) contend that during solar cycles with positive polarity, the GCR flux is doubled.  This strongly implicates Galactic Cosmic Ray (GCR) flux in modulating global temperature trends.  The lower peak amplitudes for even solar cycles and the higher peak amplitudes for odd solar cycles shown in bottom figure appears to directly confirm the kind of influence on terrestrial climate postulated by Svensmark in Influence of Cosmic Rays on Earth’s Climate (1998). From the pattern indicated, the implication is that the “warming” of the late 20th century was not so much warming as it was less cooling than in each preceding solar cycle, perhaps relating to the rise in geomagnetic activity. 

Read more of this important new two part series Part I and Part 2.