Guest essay by H. Luedecke and C.O.Weiss
We reported recently about our publication  which shows that during the last centuries all climate changes were caused by periodic ( i.e. natural ) processes. Non-periodic processes like a warming through the monotonic increase of CO2 in the atmosphere could cause at most 0.1° to 0.2° warming for a doubling of the CO2 content, as it is expected for 2100, within the uncertainty of the analysis.
We find that 2 cycles of periods 200+ years and ~65 years determine practically completely the climate changes. All other cycles are weaker and non-periodic processes play no significant role. ( See Fig. 4 )
The ~65 year cycle is the well-known, much studied, and well understood “Atlantic/Pacific oscillation” ( AMO/PDO ). It can be traced back for 1400 years. The AMO/PDO has no external forcing it is “intrinsic dynamics”, an “oscillator”.
Although the spectral analysis of the historical instrumental temperature measurements  show a strong 200+ year period, it cannot be inferred from these with certainty, since only 240 years of measurement data are available. However, the temperatures obtained from the Spannagel stalagmite show this periodicity as the strongest, by far, climate variation since about 1100 AD.
The existence of this 200+ year periodicity has none the less been questioned, doubting the reliability of temperature determinations from stalagmites. ( Even though the temperatures from the Spannagel stalagmite agree well with the temperatures derived from North Atlantic sedimentation; and even though the solar “de Vries cycle”, which has this period length and agrees in phase, is known for a long time as essential factor determining the global climate. )
A perfect confirmation for the existence and the dominant influence of the 200+ year cycle, as found by us  and with it the definite proof of absence of CO2 influence on the climate, is now provided by a recent paper  which analyses solar activities for periodic processes.
Fig. 1 Spectrum of solar activity showing the 208 year period as the strongest climate variation
The spectrum Fig. 1 ( Fig. 1d of  ) shows clearly a 208 year period as the strongest variation of the solar activity.
Fig. 2 ( Fig. 4 of  ) gives the solar activity of the past until today, as well as the prediction for the coming 500 years. ( This prediction is considered possible due to the ( multi-) periodic character of the activity. )
Fig. 2 Solar activity from 1650 to present ( measurement, solid line ) and prediction for the coming 500 years ( light gray: prediction from spectrum, dark gray: prediction from wavelet analysis ). Letters M,D,G denote the historical global temperature minima: Maunder, Dalton, Gleissberg
The solar activity agrees well with the terrestrial climate. It shows, in particular, clearly all historic temperature minima. Thus the future temperatures can be predicted from the activities – as far as they are determined by the sun ( the AMO/PDO is not determined by the sun ).
The 200+ year period found here , as it is found by us  is presently at its maximum. Through its influence the temperature will decrease until 2100 to a value like the one of the last “little ice age” 1870.
The wavelet analysis of the solar activity Fig. 3 ( Fig. 1b of  ) has interesting detail. In spite of its limited resolution it shows ( as our analysis of the Spannagel stalagmite did ) that the 200+ year cycle set in about 1000 years ago. This oscillation appears, according to Fig. 3, regularly all 2500 years. ( The causes for this latter 2500 year periodicity are probably ununderstood at present.)
Fig. 3 Wavelet analysis ( showing which oscillations were active at which time ) of solar activity. The dominant oscillations (periods between 125 years and 250 years) are clearly recognizable and recurring every 2500 years
Summarising: the analysis of solar activity proves the existence and the strength of the 200+ year periodicity which we found from historical temperature measurements, as well as from the Spannagel stalagmite data. This 200+ year cycle is apparently the one known as “de Vries cycle”.
This solar “de Vries cycle” together with the AMO/PDO determine practically completely the global climate of the past ( Fig. 4 ). This rules out any significant influence of CO2 on the climate. The latter is not surprising in view of the small amount of CO2 in the atmosphere and its weak infrared absorption cross section (also in view of the various proves of NEGATIVE water feedback ).
Fig. 4 ( Fig. 6 of  ) Measured temperatures ( black ) and constructed from the strongest 6 Fourier components ( red ). The Fourier analysis yields the 200+ year cycle for the main excursion: the drop of temperature from 1780 to 1870 and its subsequent rise to the present. This cycle was confirmed by the stalagmite data  and is again now confirmed by the solar activity  . One can see that the temperature is determined essentially by the 200+ year cycle superimposed with the 65 year cycle.
Fig. 5 Predicted global temperature of “official” models ( red ) and real ( measured ) global temperature ( green ), arbitrarily adjusted to agree at 1980. Source: Met Office
The present “stagnation” of global temperature ( Fig. 5 ) is essentially due to the AMO/PDO: the solar de Vries cycle is presently at its maximum, around which it changes negligibly. The AMO/PDO is presently beyond its maximum, corresponding to the small decrease of global temperature. Its next minimum will be 2035. Due to the de Vries cycle the global temperature will drop until 2100 to a value corresponding to the “little ice age” of 1870.
One notes that in Fig.5 the curves were adjusted to agree at 1980. Correctly they should agree for preindustrial times. Such correct adjustment would probably increase the discrepancy between models and reality further substantially.
One may note, that the stronger temperature increase from the 1970s to the 1990s, which is “officially” argued to prove warming by CO2 is essentially due to the AMO/PDO.
 Multi-periodic climate dynamics: spectral analysis of long-term instrumental and proxy temperature records. H.Luedecke, A. Hempelmann, C.O.Weiss; Clim. Past. 9 (2013) p 447
 Prediction of solar activity for the next 500 years. F.Steinhilber, J.Beer; Journ. Geophys. Res.: Space Physics 118 (2013) p 1861
Note: By publishing this, I offer it for discussion and consideration, I don’t explicitly endorse its methodology or conclusion as I have seen a number of curve fitting and cyclical exercises before that are able to extract cycles and then hindcast fit those cycles. This may be one of those instances, so I urge caution in consideration of the claim. On the plus side, I did find this Nature SR article that shows a 208 year cycle (Seuss cycle) in Indian Monsoon data., and of course we know that there is a 65 year cycle in the AMO as outlined here. – Anthony