Guest contribution by Martijn van Mensvoort

Warming on top of a conceptual 66-year cycle with an amplitude of 0.12°C (see the oscillating sine wave) after removal of the ENSO cycle; the ENSO cycle is shown in the lower part of the illustration. The most important volcanic influences are also featured + the influence of the sunspot cycle is made visible as well inside the upwardly directed trend channel.


As early as 2004 the scientific literature recognizes that an extension of the definition for the climate from “minimum 30 years” to “minimum 50 years” is necessary because of the natural variability. Since at least 2012, Dutch KNMI researchers have publicly acknowledged that a 30-year period is too short for studying weather extremes in the context of climate change.
This article describes why a doubling to at least 60 years for the described duration in the definition of climate is desirable; this finding is based on the impact of the ENSO cycle + a 66-year cycle in the HadCRUT4 temperature series. The ‘satellite-era’ only started 40 years ago in 1979; the question now arises as to whether technology may even become an obstacle to actively avoiding overestimating both trends in global warming and the impact of CO2. For the time being, the old paradigm in the definition of the climate concerning the duration of “at least 30 years” seems to indicate that within this branch of science a ‘consensus’ is being used based on outdated principles. This report demonstrates how the structural impact of global warming is being overestimated by the IPCC by about a factor of 2 due to the use of an approach based on a too short analysis period.


Op basis van natuurlijke variabiliteit wordt in de wetenschappelijke literatuur al sinds 2004 herkend dat een oprekking in de definitie voor het klimaat van “tenminste 30 jaar” naar “tenminste 50 jaar” noodzakelijk is. Door onderzoekers van het KNMI wordt sinds 2012 inmiddels erkend dat de periode van 30 jaar te kort is voor het bestuderen van weerextremen in het perspectief van klimaatverandering. In dit artikel wordt op basis van de combinatie van de ENSO cyclus en een 66-jarige cyclus m.b.v. de HadCRUT4 temperatuur serie beschreven waarom een verdubbeling naar tenminste 60 jaar voor de beschreven tijdsduur in de definitie van klimaat gewenst is. In het perspectief van het ‘satelliet tijdperk’ dat pas 40 jaar terug in het jaar 1979 is begonnen, ontstaat hierbij de vraag of technologie mogelijk zelfs een obstakel is gaan vormen om actief te vermijden dat zowel de trends in de opwarming als de impact van CO2 worden overschat. Voorlopig lijkt het achterhaalde paradigma in de definitie van het klimaat betreffende de tijdsduur van “tenminste 30 jaar” een indicatie dat binnen deze tak van wetenschap wordt gewerkt met een ‘consensus’ op basis van achterhaalde principes. In het vervolg wordt aangetoond dat de structurele impact van de trend in de opwarming wereldwijd door het IPCC met ongeveer een factor 2 wordt overschat t.g.v. het gebruik van een benadering die is gebaseerd op een te korte analyse periode.



In November 2018, the KNMI described that the extremely hot years of 2015 and 2016 were largely caused by the internal variability of the climate through the emergence of the “strong El Nino”. According to NASA, the contribution of the ‘super El Nino’ to the average temperature worldwide for the year 2016 was approximately 0.16°C 5. The El Nino effect causes a net cooling of the ocean system and is characterized by the release of large amounts of heat and CO2 in the atmosphere7. The El Nino Southern Oscillation [ENSO] also appears to have a major impact on the annual growth of CO2 in the atmosphere; experts have estimated that the ‘super El Nino’ in 2016 contributed 25% of the growth of CO2 in the atmosphere. In a broader context, Henry’s law describes that the warming of the ocean water itself has contributed close to ~15% to the growth of CO2 in the atmosphere. Moreover, it has very recently become clear that in recent decades the ocean has also been responsible for up to 40% of the variability of CO2 in the atmosphere; climate models, on the other hand, assume that variability is mainly due to vegetation on the mainland12.

An earlier report in june 2019 demonstrates on the basis of the HadCRUT4 temperature series that ‘global warming’ is overestimated if the natural variability related to a 70-year cycle in the ocean system is not taken into account. This new report shows below that the multidecadal cycle is featured with a length of 66 years. A comparison between the 1970s, 1990s and 2010s shows that the assumed acceleration in global warming can almost entirely be attributed to the 66-year cycle. The 66-year cycle + the ENSO cycle combined appears to be responsible for more than 81% of the acceleration of the warming based on the 30-year average since the 1970s, and for more than 69% compared to the 1990s. Both natural cycles combined also largely explain the correlation between CO2 and temperature in the 21st century; ‘super El Ninos’ play a major role in this. This results in an overestimation of the impact of global atmospheric CO2 as well; this also applies to the acceleration with regard to the warming of the north pole.

After removal of the 66-year cycle (+ the ENSO cycle), an upwardly directed trend channel remains with an average temperature rise of approximately +0.09°C per decade that has now lasted about 70-90 years. This concerns less than half the expectation of +0.20°C per decade that the IPCC uses for the coming decades. Also, a projection has been made for the year 2100 from which it appears that based on the trend channel a temperature rise of +0.2°C to +0.9°C compared to the record year 2016 can be taken into account. A mix of factors plays a role in the emergence of the trend channel, such as: the growth of the world population, less use of sulphates (aerosols), changes in land use, use of greenhouse gases, and possibly a natural cycle of 200+ years (in the scientific literature this very long cycle is known as the Suess/de Vries cycle, which is related to the sunspots cycle). Since the 2nd half of the 1960s, a slight increase in ‘total solar radiation’ has had a small share in the creation of the trend channel.

An overestimation of the temperature by a factor of 2 due to natural variability can possibly imply that the impact of CO2 and other greenhouse gases is also overestimated by the IPCC with an impact of the same order.

For further reading


• I – A 66 year cycle with an upward and downward phase of 33 years
• II – Warming on top of cycle shows stable trend channel
• III – Projection for the year 2100: 0.2-0.9°C on top of record year 2016
• IV – Annual growth CO2 correlates highly with ENSO cycle
• V – 21st century: correlation temperature-CO2 based on 66-year cycle & super El Nino
• VI – 21st century: warming rate 69% lower after removal of 66-year cycle & El Nino
• VII – 30-year average: acceleration in warming almost fully explained by 66-year cycle
• VIII – Four characteristics of the 66-year cycle
• IX – Five characteristics of the warming on top of the 66-year cycle
• X – 66-year cycle may have a cosmic origin
• XI – Is the definition of ‘climate’ outdated?
• XII – Discussion & conclusion

MSc/BEng Martijn van Mensvoort
education background:

Leiden University
MSc Clinical & Health Psychology [Drs. Klinische & Gezondheidspsychologie]
1993 – 1997

Hogeschool Eindhoven (Fontys)
BEng Technical Physics [Ing. Technische Natuurkunde]
1989 – 1993