Guest Post by Javier
It is a well-known feature of climate change that since 1850 multiple climate datasets present a ~ 60-year oscillation. I recently wrote about it in the 7th chapter of my Nature Unbound series. This oscillation is present in the Atlantic Multidecadal Oscillation (AMO), Arctic Oscillation (AO), North Atlantic Oscillation (NAO), Pacific Decadal Oscillation (PDO), Length of Day (LOD), and Global (GST) and Northern Hemisphere (NHT) temperatures, with different lags (figure 1).
To me this oscillation is not a cycle because prior to 1850 it had a more variable period and it is not well identified in LIA records. Since the origin of this oscillation is unknown, models have a hard time reproducing it and it is all but ignored by the IPCC. It is a big oscillation with an amplitude of ± 0.3 °C in NHT (0.1-0.2°C in GST; figure 2). While the long-term temperature trend is unaffected by it, there is a large effect on the 30-year trends. If this oscillation is considered, most of the climate alarmism vaporizes.
This oscillation was first detected by Folland et al. (1984) in global SST and nighttime marine air temperature records, and later correlated to precipitation records in the Sahel (Folland et al., 1986). The multidecadal oscillation was isolated by Schlesinger and Ramankutty (1994) in the global mean instrumental temperature record, as a 65-70-year northern hemisphere periodicity, and attributed to internal variability of the coupled ocean-atmosphere system. It was termed the Atlantic Multidecadal Oscillation (AMO) by Kerr (2000). Scafetta has published several articles on it since 2010 (Mazzarella & Scafetta, 2012, for example). Among skeptics it has been featured prominently, for example here at WUWT:
Scafetta on 60-year climate oscillations. Anthony Watts
Claim: Solar, AMO, & PDO cycles combined reproduce the global climate of the past. Guest essay by H. Luedecke and C.O.Weiss
Models overestimate 60-year decadal trends. Guest essay by Clive Best
The Elusive ~ 60-year Sea Level Cycle. Guest Post by Willis Eschenbach
It can be reasonably postulated that the famous pause is nothing more than the manifestation of the recent end of the ascending phase of the 60-year oscillation.
On examination of figure 2 we observe two prominent peaks at 2016 and 1876, separated by 140 years and thus at a similar point in the AMO oscillation. Both also took place at the end of a solar cycle. Perhaps the 1876 and 2016 El Niño events can be considered analogs, but clearly the 1876 peak shows a bigger NHT deviation and a much stronger effect on AMO.
We may remember that as the time the Challenger Expedition took place. It was the first fully scientific oceanographic expedition and one of the most successful ones. Among its achievements we can count (Steven Varner):
– The birth of oceanography as an independent scientific field.
– The first systematic plot of currents and temperatures in the ocean.
– A map of bottom deposits that has not been changed much by more recent studies.
– An outline of the main contours of the ocean basins.
– The discovery of the mid-Atlantic Ridge (which baffled scientists at the time).
– The recording of the 26,900 feet (8,200 meters) Challenger Deep, a new record ocean depth, in the Mariana Trench.
– The discovery of 715 new genera and 4,717 new species of ocean life forms.
– The discovery of prodigious life forms even at great depths in the ocean (refuting earlier hypotheses of lifeless bottoms).
The expedition departed England in December 1872 and returned in May 1876.
Recently scientists from the Scripps Institution of Oceanography (US) and the National Oceanography Centre (UK) took the data from the Challenger expedition and compared it to the Argo data from the same locations 135 years later (Roemmich et al., 2012). The warming observed was consistent with current knowledge, but they found something very interesting:
“The 0.33 °C ± 0.14 average temperature difference from 0 to 700 m is twice the value observed globally in that depth range over the past 50 years, implying a centennial timescale for the present rate of global warming.”
In other words, the warming for the first half of the period (mostly natural) is about the same as for the second half (including the anthropogenic contribution). They conclude that the warming rate of the oceans has not accelerated with the addition of anthropogenic GHGs.
For at least 4 years (1872-1876), and during all the time the Challenger was at sea, the world was experiencing La Niña conditions. It is also probable that 1871 was a La Niña year, making it one of the longest La Niña periods in recorded history.
Most people have the idea that La Niña means cooling and El Niño means warming when it is just the opposite. When strong La Niña conditions dominate, the Pacific accumulates more and more thermal energy due to higher insolation produced by the reduction of clouds due to lower evaporation. The planet thus acquires more thermal energy in the Pacific Ocean subsurface. Then it suddenly exploded in 1876 producing the largest known El Niño in historic times. A monster El Niño right in the middle of the pre-industrial IPCC baseline period (1850-1900). This puts to shame the notion that pre-industrial climate was more congenial. It was a complete catastrophe. Terrible multi-year droughts took place in Brazil, India, China, European Russia and many other places, claiming the lives of an estimated 20-50 million people, or at the time ~ 3% of the world’s population. The world’s worst natural disaster ever (not counting pandemics). We can’t even imagine it. China lost 13 million people. In India the death toll is estimated at 5.5 million, with 58.5 million people distressed by hunger. This occurred while the British colonial government exported food and reduced relief help, due to criticisms of excessive expenditure, prompting modern accusations of a colonial genocide.
So that is the human meaning of the spike at the left of figure 2. The 1876-78 El Niño was so big that it spread over all the oceans, causing a corresponding spike in the AMO. Afterwards AMO and temperatures started going down and the world recovered. El Niño accomplished its mission of releasing the excess energy accumulated during the La Niña years.
Looking at AMO data we can see that it has another interesting decadal periodicity. It is so clear that it is visible in unsmoothed monthly data, but it is better seen with a 4.5-year moving average (figure 6).
The decadal periodicity is also present in hemispheric and global temperatures, and, in an article in 2009, Anthony Watts with Basil Copeland defended a lunisolar influence behind it:
Anthony and Basil used HadCRUT3 global data, but since AMO and temperature are so correlated (see figure 1) and AMO has less noise, I am going to stick to AMO.
The decadal periodicity in AMO has a frequency of 9.0-9.1 years (Manzi et al., 2012; figure 7)
Due to its periodicity, it has been suggested numerous times that the 9-year peak corresponds to a Lunar tidal frequency. The nodes where the orbit of the Moon crosses the Earth’s ecliptic are two points where a maximal alignment of the Moon-Earth-Sun takes place. They half rotate around the Earth every 9.3 years producing higher tides at that period when they reach optimal alignment. Also, the elliptical orbit of the Moon rotates around the Earth, placed at one of the foci, every 8.85 years. Higher tides also take place when the perigee-apogee axis is properly oriented towards the Sun. The closeness of these two periods suggests that a 9.1 period could result from their interaction.
Scafetta (2010) ingeniously demonstrated using the JPL ephemeris that the speed of the Earth around the Sun is perturbed by the presence of the Moon at a frequency of 9.1 years (figure 8).
Although this does not demonstrate that the 9-year periodicity in AMO is due to the Moon, it does build a case. The effect of the Moon’s gravitation on atmospheric tides and oceanic tides has enough energy to produce the observed effect. Half of the vertical mixing in the oceans is due to tides, and the other half to wind. In addition, tides affect oceanic currents by sloshing huge amounts of water from one place to another. The expected effect is that stronger tides should produce cooling by enhancing the upwelling and mixing of colder, deeper water. It is important to realize that the tidal forcing is thus inverted with respect to AMO temperature anomaly, and higher tidal forcing should produce temperature troughs (for example in figure 6), not peaks.
Some people have suggested that longer cycles could be the result of a modulation between lunar and solar cycles. For example Greg Goodman (climategrog) in a comment in 2014:
“If we do the same process with 9.08 and 10.4 it gives a modulation frequency of 143 years so the “beat” period of each bulge in amplitude is 71.5. So, it is possible for an interplay of lunar and solar forces to produce the kind of long cycles seen in the climate record.”
Prior to that, in 2011, Clive Best explored in an article in his blog the possibility that the 60-year oscillation was produced by the combined effect of both the solar variability and the tidal variability: A 60-year oscillation in Global Temperature data and possible explanations.
Alas, he couldn’t find convincing evidence:
“There is no single astronomical effect which can explain the 60-year time period. I have looked into the possibility that a superposition of both the 11-year solar variability and the 18.6 year lunar tide could produce the observed 60 year oscillation. There is no convincing evidence that this is the case.”
So, I decided to revisit the 60-year oscillation to see if it is possible that the modulation between the 9-year frequency in AMO and the 11-year solar cycle could be responsible for the emergence of the 60-year oscillation through constructive and destructive interference. In principle the period of the beat from a 9-year period (T(1)) and a 10.9-year period (T(2)) is too short. T(beat) = 1 / (1/T(1))–(1/T(2)) = 52 years
However, since the solar cycle is quite variable I decided to plot it anyway. The result is most interesting (figure 9).
The non-stationary correlation between the two cycles produces a periodicity that is compatible with the ~ 60-year periodicity in AMO. Periods of high correlation between the 9-year AMO and 11-year solar periodicities correspond to cold 60-year AMO periods, while periods of high anti-correlation correspond to warm 60-year AMO periods.
Mechanistically, times of high correlation between the 9-year AMO and 11-year solar periodicities correspond to times when the highest tidal forcing (AMO cooling) coincide with the times of lowest solar activity (solar minima), which could explain why the AMO displays cooling. Times of high anti-correlation between the 9-year AMO and 11-year solar periodicities correspond to times when the highest tidal forcing (AMO cooling) coincide with the times of highest solar activity (solar maxima), which could explain why the AMO does not display cooling.
The irregularity of the 11-year solar cycle period could explain why the ~ 60-year oscillation is also irregular, and the low level of solar activity during the LIA could also explain why the 60-year oscillation is not apparent or weaker at that time.
Regardless of the 60-year oscillation being due or not to the modulation of a lunar tidal 9-year cycle and a solar activity 11-year cycle, the observation of the interplay between these two cycles leads to two conservative predictions that do not rest on any hypothesis. As we are in a period of high anti-correlation and as Solar Cycle 25 increases its activity over the next 5-6 years the AMO should experience a decrease associated with its 9-year periodicity, putting additional downward pressure on surface temperatures.
The second prediction has been proposed multiple times: the downward phase of the ~ 60-year AMO oscillation should cause a reduction in global temperatures of ~ 0.1-0.2 °C over the next 20-30 years, all other things being equal.