A role for the sun in climate change

Javier Vinós & Andy May – August 28, 2022

“Once you start doubting, just like you’re supposed to doubt. You ask me if the science is true and we say ‘No, no, we don’t know what’s true, we’re trying to find out, everything is possibly wrong’ … When you doubt and ask it gets a little harder to believe. I can live with doubt and uncertainty and not knowing. I think it’s much more interesting to live not knowing, than to have answers which might be wrong.” Richard Feynman (1981)

5.1 Introduction

The 1990s discovery of multidecadal variability (see Part IV) showed that the science of climate change is very immature. The answer to what was causing the observed warming was provided before the proper questions were asked. Once the answer was announced, questions were no longer welcome. Michael Mann said of a skeptical Judith Curry: “I don’t know what she thinks she’s doing, but it’s not helping the cause, or her professional credibility” (Mann 2008). But as Peter Medawar (1979) stated, “the intensity of a conviction that a hypothesis is true has no bearing over whether it is true or not.” Scientists’ opinions do not constitute science, and a scientific consensus is nothing more than a collective opinion based on group-thinking. When doubting a scientific consensus (“just like you’re supposed to doubt,” as Feynman said) becomes unwelcome, the collective opinion becomes dogma, and dogma is clearly not science.

Lennart Bengtsson, former director of the Max Planck Institute of Meteorology, winner of the Descartes Prize and a WMO prize for groundbreaking research put it succinctly after agreeing to participate in a skeptical organization headed by Nigel Lawson, a member of the House of Lords and former Chancellor of the Exchequer:

“I had not [been] expecting such an enormous world-wide pressure put at me from a community that I have been close to all my active life. Colleagues are withdrawing their support, other colleagues are withdrawing from joint authorship etc. I see no limit and end to what will happen. It is a situation that reminds me about the time of McCarthy. I would never have expected anything similar in such an originally peaceful community as meteorology. Apparently, it has been transformed in recent years” (von Storch 2014).

This is the effect that dogmas have on scientists, normal scientific research becomes impossible by introducing a strong group-bias against questioning the dogma.

Once dogmas are established, they tend to evade scientific scrutiny. Stuart Firestein, when reviewing the main mistaken scientific consensuses of the past in his 2012 book, Ignorance: How it Drives Science, wonders if

“… is there any reason, really, to think that our modern science may not suffer from similar blunders? In fact, the more successful the fact, the more worrisome it may be. Really successful facts have a tendency to become impregnable to revision.” Stuart Firestein (2012)

The main dogma of climate change science is stated in the Fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change as:

“It is extremely likely that more than half of the observed increase in global average surface temperature from 1951 to 2010 was caused by the anthropogenic increase in GHG concentrations and other anthropogenic forcings together. The best estimate of the human-induced contribution to warming is similar to the observed warming over this period (Figure SPM.3)”(IPCC 2014).

However, there is no evidence confirming this dogma. It is based on computer model results that were programmed with the same assumptions that emerge from them, in a clear case of circular reasoning. An example of such assumptions is that the only accepted effect of solar variability on climate is the change in total solar irradiance (TSI). None of the solar effects described in Part II are included because they are not accepted, and even if they were accepted, we would not know how to program them. We don’t know how they happen or how they affect climate. Such is the hubris of modern climate theory supporters that they believe we understand how climate changes well enough to make reliable projections 75 years into the future.

Fig. 5.1. The main dogma of climate change science is shown in Figure SPM.3 from AR5. The fifth IPCC report, claims that observed 1951-2010 warming was due to anthropogenic causes, without contribution from natural forcings, despite low volcanic activity and high solar activity; and without any contribution from multidecadal oscillations, despite the 1976-2000 period of warming coinciding with an AMO upswing.

In Part III we showed the importance of meridional transport (MT) and the latitudinal temperature gradient (LTG) in both the global and regional climate. They determine the amount of energy directed toward the poles. In Part IV we showed that changes in MT cause climate regime shifts, and that these shifts alter the energy budget of the climate system. This evidence refutes the dogma, revealing that changes in MT constitute a climate forcing not accounted for in Fig. 5.1. In Part II we reviewed the evidence that changes in solar activity affect the polar vortex, ENSO, Earth’s rotation rate, and planetary wave atmospheric propagation properties, resulting in dynamical spatiotemporal changes in atmospheric circulation, temperature, and precipitation that correspond with substantial climate changes of the past as recorded by paleoclimatological evidence. Each and every one of the climatological factors affected by solar activity points to an effect of the variable sun on MT. Through changes in MT, changes in solar activity constitute one of the main causes of climate change, further refuting the climate dogma.

5.2 Meridional transport multiple regulation

MT is the most important modulator of global climate. The great complexity of the ocean-atmosphere coupled global circulation with all its modes of variability, oscillations, teleconnections, and modulations, is just the manifestation of a single underlying cause, the transport of energy from its climate system entry point to its exit point. Mass (including water) is transported, directly or indirectly, because of energy transport. As we saw in Part III, section 3, MT is mainly carried out by the atmosphere (see Fig. 3.4), and it does so through two separate but coupled tracks, one is through the stratosphere (the Brewer–Dobson circulation, BDC), the other is through the troposphere, mainly over ocean basins with both the atmosphere and ocean contributing. The coupling of these two tracks is variable in time and space (Kidston et al. 2015). At the equatorial zone there is coupling through deep-convection and the ascending branch of the BDC (Collimore et al. 2003), and at high latitudes through the polar vortex (PV). The downward coupling in the mid-latitudes is complex and variable by longitude (Elsbury et al. 2021). The downward coupling is mainly exerted by changes in stratospheric temperature gradients and the response of the wind thermal balance. The wind thermal balance affects the strength of the mean zonal circulation, and the position and strength of tropospheric jets, eddies, and storm tracks (Kidston et al. 2015). The upward coupling depends on changes in convection and atmospheric wave generation. Consequently, the coupling is stronger in winter when temperature contrasts and atmospheric wave generation in the troposphere are more intense, and temperature gradients in the stratosphere are deeper.

Fig. 5.2. Meridional transport diagram. The light-grey rounded rectangles are the two components (tracks) of meridional transport, with their known modulators in white ovals. Black arrows indicate coupling or modulation. Dashed arrows indicate the indirect effect from volcanic eruptions on tropospheric meridional transport and ENSO.Changes in meridional transport affect the energy budget of the Earth’s climatic system by changing the energy transfer intensity from the GHG-rich tropical region to the GHG-poor polar region. From Vinós 2022.

Stratospheric MT is modulated by factors that alter the latitudinal temperature gradient (ozone, solar activity, and volcanic aerosols), or the zonal wind strength (QBO), as they determine the level of planetary wave transmission that powers stratospheric transport. ENSO is part of the tropospheric MT and is determined by its conditions, but it is also a modulator of stratospheric transport, affecting the strength of the BDC (Domeisen et al. 2019), and thus participates in the stratosphere-troposphere MT coupling. Whether the QBO influences ENSO is not known, but all other interactions between these three modulators (solar effect, QBO and ENSO) of stratospheric MT have been documented (Labitzke 1987; Calvo & Marsh 2011; Salby & Callaghan 2000; Taguchi 2010). The stadium-wave represents the coordinated sequential change affecting the interconnected parts of tropospheric MT (Wyatt & Curry 2014). It is a strong multidecadal oscillation in MT, and the importance it has on climate variability cannot be overstated.

Most of the climatic effects from volcanic activity that are not due to the direct reflection and scattering of solar radiation by stratospheric sulfate aerosols, or altered stratospheric chemistry, are accomplished by altering MT. That is why strong tropical volcanic eruptions cause NH winter warming by strengthening the PV (GuðlaugsdÓttir et al. 2019), why they induce ENSO states (Swingedouw et al. 2017; Sun et al. 2018), and why they excite the bidecadal MT oscillation (Swingedouw et al. 2015; see Part IV, Sect. 4.2 & Fig. 4.2), accounting for the interdecadal effects of volcanic eruptions.

Other than variations in the GHG content of the atmosphere, climate changes through changes in MT, and this is likely the main mechanism, since important climatic changes have occurred in the past with only modest variations in greenhouse radiative forcing. The effect of some MT modulators trends to zero when averaged over a few years. This is the case with QBO and ENSO. Multidecadal variability also balances out over longer time frames. However, solar activity has centennial and millennial cycles that become the most important MT modulator at sub-Milankovitch frequencies (i.e., <10,000 years). The Medieval Warm Period, centered c. 1100, the Little Ice Age, centered c. 1600, and the ongoing Modern Global Warming period, coincide with a millennial solar activity cycle, known as the Eddy cycle (Abreu et al. 2010), that displayed high solar activity during the medieval and modern solar maxima (c. 1150 & 1970), and low solar activity at the Wolf, Spörer, and Maunder cluster of Solar Minima (c. 1300–1700).

Centennial and millennial changes in solar activity are an important climate forcing because of the persistent effect they have on MT. Solar activity changes alter the global climate system energy budget. Shorter changes in solar activity (decadal) are less important because at these time frames MT becomes more affected by other modulators, like the stadium-wave, ENSO and the QBO, that quite often act in opposition to solar modulation.

5.3 The Winter Gatekeeper Hypothesis

The current view of climate change, as reflected in the IPCC assessment reports, constitutes a radiative theory of climate. Within this theory, solar variability is only considered in terms of the small radiative changes in TSI (about 0.1 % per solar cycle), despite strong evidence of solar-induced dynamical changes to the global atmospheric circulation presented in Part II. These non-linear, indirect, dynamical effects of solar variability on climate are detectable in climate reanalysis (see Fig. 2.2; Lean 2017), and reproduced by models (Kodera et al. 2016), yet they are not incorporated to the modern climate change theory because no room has been left for them.

The change in solar activity does not have a year-round global effect as expected from a global change in solar radiative forcing. The effect is higher during hemispheric cold seasons, and maximal during the boreal winter, as shown by its modifications to the Earth’s rotation speed (see Fig. 2.5; Le Mouël et al. 2010). The changes in the length of day (ΔLOD) are due to changes in the meridional atmospheric circulation responsible for the increase in the amount of heat transported to the winter pole. This cold-season specific solar effect, tied to the strength of the PV, is seen in climate reanalysis and observations suggesting it affects both atmospheric and oceanic phenomena, including the AO and NAO, blocking events frequency, zonal wind strength, the sub-polar gyre strength, and the North Atlantic winter storm track. The season-specific dynamical effect of solar activity must result in important changes in the amount of heat directed to the dark pole. Most of this heat exits the planet radiated as OLR in the long polar night. Heat flux across sea-ice is always towards the atmosphere, and the increase in non-condensing GHGs favors energy loss through higher radiative cooling from GHG molecules that are warmer than the surface (van Wijngaarden & Happer 2020). Radiative heat loss also increases due to the strong decrease in cloud cover that accompanies the polar winter (Eastman & Warren 2010), and the low absolute humidity of the winter polar atmosphere.

The seasonal asymmetric effect of solar activity on climate establishes solar variability as the most important long-term gatekeeper of the large amount of heat that leaves the planet at the poles every cold season. They are the main heat sink for the planet (see Fig. 3.2). Thus, the hypothesis of how changes in solar activity regulate MT is named the Winter Gatekeeper hypothesis (WGK-h). The WGK-h (Fig. 5.3) states that the level of solar activity is one of several factors that determine the strength of zonal winds and thus the propagation of planetary waves in the winter atmosphere. Poleward and upward wave propagation controls PV strength, which is the main modulator of heat and moisture MT to the winter pole. Winters of high solar activity promote stronger zonal circulation, reducing MT, leading to a colder Arctic winter, warmer mid-latitudes winter, a warmer tropical band due to reduced BDC upwelling, and lower energy loss at the winter pole. Winters of low solar activity promote the opposite. The difference in energy loss at the winter pole is large enough to greatly affect the climate of the entire planet when solar activity is consistently high or low for several consecutive solar cycles (i.e., decades).

Fig. 5.3 The Winter Gatekeeper hypothesis of solar variability effect on climate. a) High solar activity winters promote a strong stratospheric latitudinal temperature gradient through increased ozone and enhanced ozone heating caused by higher UV radiation. High solar activity, through changes in the thermal wind balance, strengthens the zonal winds reducing planetary wave propagation. This allows the polar vortex to remain strong through the winter, reducing meridional transport and heat loss at the winter pole. The effect on the stratospheric temperature gradient from high solar activity can be opposed by easterly QBO and El Niño conditions. Tropospheric meridional transport is strongly affected by the c. 65-year oscillation, here represented over the Atlantic by the AMO, that denotes a weaker transport when it changes to higher values (heat accumulation in the North Atlantic). The climatic effect is enhanced global warming and a cold Arctic/warm continents winter pattern. b) Low solar activity winters promote a weak stratospheric latitudinal temperature gradient due to lower UV radiation, leading to a weak polar vortex that increases meridional transport and heat loss at the winter pole. The effect on the stratospheric temperature gradient from low solar activity can be opposed by westerly QBO, La Niña conditions, and volcanic aerosol forcing. The tropospheric meridional transport is strong when the c. 65-year oscillation is in the descending phase, and the AMO is changing to lower values (heat reduction in the North Atlantic). Increased transport increases Earth’s speed of rotation as zonal winds decrease, and less angular momentum resides in the atmosphere. The climatic effect is reduced global warming and a warm Arctic/cold continents winter pattern. From Vinós 2022.

The WGK-h is based on the evidence that MT is one, if not the most important, agent for climate change. But as stated previously, MT is modulated by climatic conditions that affect the strength of zonal winds, including not only solar activity but also ENSO, the QBO, stratospheric volcanic aerosols, and the stadium-wave (the multidecadal oscillation in tropospheric MT). As MT depends on atmospheric and oceanic transport, it responds not only to the stratospheric signal that involves solar activity, but also to a tropospheric one that involves the ocean (Fig. 5.3). This double dependency leads to an inconsistency in solar effects that has plagued solar-climate studies. The solar signal is part of a complex system that determines the strength of winter MT, but its long turnover rate (decadal to centennial) accumulates over time.

The mechanisms for the solar effect on climate have been described by multiple authors. Differential heating of ozone by UV, creates a temperature gradient in the stratosphere that affects zonal wind strength. The strength of zonal winds determines planetary wave propagation that affects PV strength. Zonal wind and PV conditions in the stratosphere propagate to the troposphere through thermal wind balance and stratosphere-troposphere coupling. At the troposphere, the position and strength of the jets and the conditions of the Arctic Oscillation are affected (Lean, 2017). However, the WGK-h proposes that the long-term climatic effect of solar variability is mediated through its effect on the MT of heat towards the winter pole, and that the stronger global climatic effects are due to cumulative energy loss at the winter pole during prolonged periods of low solar activity. The main role for solar variability in climate is to act as a winter gatekeeper, promoting energy conservation during years of high solar activity and allowing a higher energy loss during years of low solar activity. As MT is geographically variable, the solar energy gatekeeping role has a stronger effect in the North Atlantic winter storm track and a smaller effect at the south polar cap, with the Pacific and Siberian Arctic winter gateways falling in between.

The WGK-h provides an explanation for the strong paleoclimatic effect of periods of prolonged low solar activity, like the Little Ice Age (LIA), and its alternation with warmer periods like the MWP or Modern Global Warming that correspond to the c. 1000-yr Eddy solar cycle as revealed by solar and climate proxies (Marchitto et al. 2010). It can also explain the North Atlantic region behavior as a climate variability hotspot. Paleoclimatologists have long noticed that many prominent climate change manifestations, such as Bond events, Dansgaard–Oeschger events, Heinrich events, the MWP or the LIA are more prominent or exclusive to the North Atlantic region. This region is a preferred corridor for MT and, thus, it is the area that is most sensitive to changes in it.

5.4 Evidence for the Winter Gatekeeper hypothesis

The WGK-h explains how the known short-term dynamical effects of solar UV variability on atmospheric circulation (i.e., the top-down mechanism; Matthes et al. 2016) are responsible for an outsized longer-term modulation of climate change, through persistent changes in MT that alter the radiative properties of the planet.

The effect of solar variability on climate on a centennial to millennial timescale has long been established by paleoclimatology (Engels & van Geel 2012), but this knowledge could not be incorporated to our understanding of climate change because of the lack of a known mechanism. Solar variability during the Holocene is relatively well known through the cosmogenic isotope record (mainly ¹⁴C and ¹⁰Be records). The LIA is not the only secular period of the Holocene where an association can be established between persistently reduced solar activity in the form of solar grand minima (SGM) and a significant cooling in the Northern Hemisphere, together with a change in precipitation patterns that affected large regions, including the tropical monsoons (Wang et al. 2005b). At c. 11.4 kyr BP the Pre-Boreal SGM coincides with the Pre-Boreal Oscillation (Björck et al. 1997). At c. 10.3 kyr BP the Boreal 1 SGM coincides with the Boreal Oscillation 1 (Björck et al. 2001). At c. 9.3 kyr BP the Boreal 2 cluster of SGM coincides with the Boreal Oscillation 2 (Zhang et al. 2018). Between 7.7 and 7.2 kyr BP a LIA-like period coincides with the Jericho cluster of SGM (Berger et al. 2016). At c. 6.3 kyr BP another period of low solar activity coincides with another climate pessimum (Fleitmann et al. 2007). At c. 5.2 kyr BP the large global glacier advance that froze Ötzi the iceman in the Alps coincided with the Sumerian cluster of SGM (Thompson et al. 2006). At c. 2.8 kyr BP, another climate pessimum identified with the Great Winter of the Bronze Age Nordic sagas (Fries 1956) coincided with the Homeric SGM (Chambers et al. 2007). And at c. 0.5 kyr BP the LIA coincided with the Wolf, Spörer, and Maunder cluster of SGM (Kokfelt & Muscheler 2012). Twenty-five SGM have been identified during the Holocene (Usoskin 2017), but since 12 of them belong to 4 clusters, there are 17 periods of persistently reduced solar activity in 11,700 years. Despite the difficulties of studying the climate of past millennia, half of them have already been convincingly related to periods of profound climate worsening, in some cases associated with human population struggles (see Fig. 2.1; Bevan et al. 2017). It is not surprising that so many paleoclimatologists are convinced solar variability has a profound effect on climate change (Rohling et al. 2002; Hu et al. 2003; Engels & van Geel 2012; Magny et al. 2013).

The WGK-h requires that solar modulation of climate is accomplished by the top-down dynamical mechanism acting on MT. Colin Hines conceived the bases of the top-down mechanism in 1974, and the first evidence was published by Joanna Haigh in 1996, incorporating the crucial role of ozone as the UV variability sensor and transmitter. Since then, the top-down mechanism has found support in observations, reanalysis, and modeling (Gray et al. 2010; Gruzdev 2017; Kodera et al. 2016). The WGK-h links the top-down mechanism to the detected long-term effects of solar variability on climate through persistent modifications to the most important climate variable, the MT of energy from the tropics to the poles.

The WGK-h is supported by evidence of a solar effect on climate that is otherwise difficult to incorporate into alternate hypotheses. It explains why the semi-annual component of the changes in the Earth’s speed of rotation, manifested as changes in the length of day (∆LOD; see Part II), responds to changes in solar activity (Le Mouël et al. 2010). The LOD changes are a manifestation of the solar modulation of the winter atmospheric circulation. It also explains why the multidecadal trend in ∆LOD changes correlate with climatic changes (Lambeck & Cazenave 1976; Mazzarella, 2013).

Solar modulation of ENSO (see Part II) also supports the WGK-h. Low solar activity promotes a stronger MT, favoring La Niña conditions at the equatorial Pacific, probably in response to a higher BDC upwelling through tropical stratosphere-troposphere coupling. This is the opposite of tropical volcanic eruptions which produce a weaker MT and stronger PV, inducing El Niño conditions in the equatorial Pacific probably through a reduction in tropical upwelling by the opposite mechanism.

The warm Arctic/cold continents (WACC) winter pattern, linked to low solar activity (Kobashi et al. 2015; Porter et al. 2019), also constitutes evidence for the WGK-h. During prolonged periods of low solar activity, the Arctic is characterized by warmer winters, while the mid-latitude continents suffer colder winters due to more frequent incursions of polar air masses. The opposite happens during prolonged periods of high solar activity, explaining why Arctic sea-ice initiated a great reduction at the climatic shift of 1997 (see Part IV) and not during the previous decades of prominent global warming. Arctic amplification since 2000 manifests as a cold season phenomenon, with little summer temperature increase, supporting the underlying seasonal changes in MT that have taken place.

As required by the hypothesis, stratospheric planetary wave amplitude is modulated by solar activity (Powell & Xu 2011; see Fig. 2.8), with low solar activity resulting in increased planetary wave amplitude that should promote a stronger BDC and weaker PV.

The biennial oscillation (BO) changes the PV from a strong configuration one winter to a weak configuration the next (Fig. 5.4a). It results from the solar cycle modulation of the QBO bimodality and its interaction with the strong polar annual variation (Baldwin & Dunkerton 1998; Salby & Callaghan 2006; Christiansen 2010). After the 1976–77 climate shift, the bimodality in the QBO and the BO weakened, resulting in a predominantly strong-vortex phase (Fig. 5.4a; Christiansen 2010). At the 1997–98 climate shift, the bimodality in the QBO and the BO changed again to a stronger-bimodality weaker-vortex phase. These climate shifts define the 1977–97 period when the effect of the QBO on the strength of the PV by the Holton–Tan mechanism weakened considerably (Lu et al. 2008; see Part II). In the 1970s, the QBO at 50 hPa, and extratropical winds at 54°N and 10 hPa broke their correlation while becoming more predominantly westerly (positive) as shown by their cumulative value (Fig. 5.4b; Lu et al. 2008), weakening the winter coupling between the QBO and the PV for the period 1977–97, as stronger westerly winds hinder the propagation of lower amplitude planetary waves. The stronger PV that resulted from the high activity solar cycles 21 and 22 produced a slight cooling trend in winter Arctic temperature (Fig. 5.4c, grey area), while the weaker PV that resulted from the lower activity of solar cycles 20 and 23 (and 24) resulted in warming trends in the winter Arctic (Fig. 5.4c, white areas). The relationship between the strength of the PV and winter Arctic surface temperature is very clear. Notice that winter Arctic temperature evolution is opposite to NH temperature evolution, underscoring their negative correlation.

Fig. 5.4. Polar vortex, zonal wind, Arctic temperature, and the solar cycle. Vertical dashed lines mark the solar minima, and the gray area corresponds to the climate regime period between the 1976 and 1997 climate shifts. a) October–March mean vortex at 20 hPa, as the leading principal component of the mean geopotential height north of 20°N empirical orthogonal function, from the NCEP/NCAR reanalysis dataset. Higher values denote a strong vortex for that winter. Circa 1976 a regime shift took place from a generally weak vortex displaying bimodality to a stronger vortex with unimodality. The opposite shift took place c. 1997. Dotted lines are average values for the periods separated by 1976 and 1997. After Christiansen 2010. b) Black line, cumulative of the 3-year averaged November–March average zonal-mean zonal wind speed at the equator at 50 hPa. Grey line, cumulative 3-year averaged November–March average zonal-mean zonal wind speed at 54.4°N at 10 hPa. Dotted lines are linear trends for the cumulative 54.4°N data for the periods 1959–65, 1965–76, 1976–97 and 1997–2004. Data after Lu et al. 2008. c) Winter (December–February) mean temperature anomaly calculated from the operational atmospheric model at the European Center for Medium-range Weather Forecast for the +80 °N region. The dotted lines are linear trends as in (b) except the last period ends in 2010. Data from the Danish Meteorological Institute. d) Black line, number of sunspot spotless days in a running 6-month window. Gray line, monthly sunspots. Horizontal dotted lines are the average monthly number of sunspots for each solar cycle (SC). Data from WDC–SILSO. From Vinós (2022).

As required by the WGK-h, seasonal patterns of 80–90 °N temperature anomaly display very important changes over time. Arctic summer and winter temperature anomalies did not display any significant long-term deviation from average during the 1970–99 period, indicating a surprising difference from the global warming experienced by most of the planet at the time, and in stark contrast to the polar amplification predicted by theory and the climate models. Starting in 1997, the Arctic summer temperature anomaly displays a small decrease of about half a degree (see Fig. 4.6a), while the Arctic winter temperature anomaly shows a huge increase reaching +8 °C average during the 2017–18 winter (Fig. 5.5). The heat responsible for this winter temperature increase is transported to the Arctic from lower latitudes (see Part III). It is paradoxical and contrary to the prevalent view, that Arctic warming was less pronounced during the rapid global warming period of the 1980s and 1990s and is more pronounced during the recent period of reduced warming, often called the pause or hiatus in global warming. This apparent contradiction can be resolved if solar activity regulates the amount of heat directed to the poles during the winter. According to the WGK-h, the increase in winter poleward heat transport responsible for the temperature increase in the Arctic in that season is contributed by the persistent decrease in solar activity since 2004. The negative correlation between long-term solar activity and Arctic winter temperature is clear (Fig. 5.5).

Fig. 5.5. Arctic winter temperature is solar modulated. Black curve, smoothed 10.7 cm solar flux as a proxy for solar activity. The third order polynomial least-squares fit has been calculated with all the data available since 1947 to reduce the border effect in the graphed data. Data from the Royal Observatory of Belgium STAFF viewer. Red curve, winter (December-February) mean temperature anomaly calculated from the operational atmosphere model at the European Center for Medium-range Weather Forecast for the +80 °N region, with a third order polynomial least-squares fit. Data from the Danish Meteorological Institute. From Vinós (2022)

The solar-induced changes in the Arctic have many consequences. The WGK-h requires an increase in cold-season Arctic OLR when decadal solar activity decreases. This increase was observed in the 1997 climate regime shift (see Fig. 4.7). The increased energy loss at the poles since 1997 must have contributed to the pause in global warming. At the same time the strong wintertime warming in the Arctic has little effect on the regional cryosphere, since Arctic winter temperature is c. 25 °C below freezing on average. Meanwhile, the modest summer temperature decrease has a stabilizing effect on summer sea-ice extent that displays a pause since 2007 (Fig. 5.6). Paradoxically, the big increase in yearly averaged Arctic temperature is being publicized as evidence of hefty Arctic amplification, yet it coincides with a pause in Arctic summer sea-ice extent change that might even lead to a modest increase over the present solar cycle (SC25, 2020–c. 2031). Unless the Arctic temperature increase is seasonally analyzed, it is difficult to understand what is happening, but then it becomes clear that Arctic amplification is not an amplification of global warming. Arctic winter warming is a strong indication that the climatic effect of solar variability is being profoundly misunderstood, and the contribution from the MSM in solar activity to modern global warming is much larger than accounted for in the IPCC reports and current climate models. A clear prediction from this hypothesis is that the Arctic winter temperature anomaly will start to decrease when a new more active solar cycle takes place. This could happen with solar cycle 26, which is predicted to increase in activity c. 2032 (Fig. 5.7). That decrease in temperature should be accompanied by an increase in Arctic sea-ice.

Fig. 5.6. Projections of Arctic sea-ice decline. Model simulations (continuous colored lines, 2006–2090), and observations (black line, 1935–2021) of Arctic sea-ice extent for September. Colored lines for RCP scenarios are model averages from CMIP5, after Walsh et al. (2014). Light Brown dashed line is a model based on the known 60 and 20-year periodicities in Arctic sea-ice. Black continuous line is NSIDC September Arctic sea-ice extent for the satellite window (1979–2021), while 1935–1978 September Arctic sea-ice extent data is from Cea Pirón & Cano Pasalodos (2016) reconstruction. Dark red dashed line is a sigmoid survival curve fitted to 1979–2012 data with ice-free conditions near 2030, following the Arctic sea-ice death spiral proposed by Mark Serreze (2010). The conservative projection, the lighter brown dashed line, explains the pause in Arctic sea-ice melting since 2007 and suggests over 2 million km² of Arctic sea-ice remaining by summer 2100. From Vinós 2022.

Fig. 5.7. Sunspot forecasting based on solar activity cycles. a) 1700–2020 international annual sunspot number, along with the rising linear trend. The centennial Feynman periodicity is shown as a sinusoidal curve with minima at the times of the lowest sunspot numbers, defining the centennial periods F1 to F3. Their span is dictated by the dates below. The F3 period displays the highest number of sunspots of the three. F2 period was affected by the presence of a de Vries bicentennial cycle low at SC12–13 and displays less sunspots than the other two. Source of data: WDC–SILSO, Royal Observatory of Belgium, Brussels. b) Solar model built on the spectral properties of solar activity from cosmogenic and sunspot records. The model assumes default maximum activity for each cycle that is then lowered by the distance to the lows of the five cycles considered, the 2500-yr, 1000-yr, 210-yr, 100-yr, and 50-yr cycles. Cycle dates and periods deduced from past activity are projected into the future, producing a solar activity forecast for 2022–2130. F4 is projected to coincide with a peak in the millennial Eddy cycle identified from Holocene solar proxy records, and likely to have as many sunspots as F3 despite another de Vries cycle low expected for SC31–32. SC1, SC10, SC20, and SC29 constitute lows in the pentadecadal solar periodicity, which reduces sunspot numbers at the peak of the centennial periodicity. The model (Vinós 2016) does not project maximum activity (more variable), but the sunspot sum over the entire cycle. The 2016 model was correct in forecasting SC25 activity higher than SC24 and lower than SC23. Now it forecasts increased solar activity from SC24 to SC28. From Vinós 2022.

5.5 The asymmetric High-solar/Low-effect — Low-solar/High-effect paradox

Since the sun powers the climate system it is logical to assume that a more active sun, by providing more energy, should have a proportional effect on climate, that is opposite to the effect of a decrease in energy by a less active sun. However, the study of paleoclimatology shows that this is not the case. Solar activity effect on climate is highly asymmetric, with low solar activity having a much more profound effect on climate than high solar activity.

The study of solar paleoclimatology was pioneered by Andrew Douglass (1919) and revived by the landmark study of John Eddy (1976) on the Maunder minimum. SGM throughout the Holocene and their associated climatic effects have been identified by many authors (Vinós 2022). The SGM from the past 1,000 years have received the names of astronomers, while those for the previous 7,000 years received names taken from human history (see above and in Vinós 2022). What is glaringly lacking is the corresponding identification, naming, and climatic studies of solar grand maxima. While they can be mathematically defined on the solar activity record (Usoskin 2017), only the two most recent ones, the medieval solar maximum and the modern solar maximum have been named. Paleoclimatic studies do not produce an obvious high solar activity-climate association. It appears solar grand maxima leave a much smaller footprint on the paleoclimate record than SGM.

What paleoclimatology is telling us is that solar-climate scientists should pay more attention to the effect of low solar activity on climate. The WGK-h helps explain why low solar activity has a stronger effect on climate than high solar activity.

The 11-yr solar cycle maximum is a lot more variable than the solar minimum. Although sunspots are perhaps not the best way to gauge solar activity during solar minima, the sunspot record (13-month smoothed; SILSO 2022) shows that solar maxima have varied between 81 sunspots in 1816 and 285 in 1958, a 204-sunspot difference. By contrast solar minima have varied only between 0 sunspots in 1810, and 18 sunspots at the highest minimum in 1976, an 18-sunspot difference. During a solar grand maximum, like the modern one (1935-2005; see Fig. 1.6), 6 years of high or very high solar activity are followed by 5 years of low or very low solar activity. During a SGM all years, decade after decade, have low or very low solar activity.

When solar activity is low the effect of the equatorial stratosphere on the PV (Holton–Tan effect) is stronger and the PV becomes anomalously weaker. Thus, at solar minimum the solar effect is maximum. The biggest positive deviations from trend in winter Arctic temperature usually take place during solar minima (Fig. 5.5). The climatic shifts of 1976 and 1997 took place at the solar minimum, which is evidence of the WGK-h. The 1925 shift also took place right after the SC15–16 minimum, and the 1946 shift after the SC17–18 minimum (see Fig. 4.8c & f; Mantua et al. 1997). Solar activity level between minima determines the level of equatorial-polar atmospheric coupling and the Arctic climate over that cycle (Fig. 5.4d). Since regime shifts in atmospheric circulation and climate appear to take place at solar minima, over the following years the activity of the solar maximum determines if a shift takes place. If the activity is similar to the prior cycle there is no shift, if it is markedly different the shift starting at the solar minimum is confirmed. A predictable result is a high frequency of climate phases that span two solar cycles, like the 1976–1997 period. This explains the repeated reports of 22-year solar signals in climate proxies, like the bidecadal drought rhythm in the western US (Cook et al. 1997), or tree-ring width in the Arctic (Ogurtsov et al. 2020) and Southern Chile (Rigozo et al. 2007).

Thus, the WGK-h provides an explanation for the asymmetric solar effect paradox. According to the hypothesis, years of high solar activity result in less energy loss at the winter pole due to a stronger PV and reduced MT (Fig. 5.3a), while years of low solar activity result in more energy lost from the opposite effect (Fig. 5.3b). During high activity solar cycles, 5-6 years of above average solar activity promote lower energy loss at the poles, followed by 4-5 years of below average solar activity that promote higher energy loss at the poles, resulting in moderate warming. During low activity solar cycles, all or nearly all years display below average solar activity resulting in intensified cooling.

The asymmetry in the 11-year cycle variability and in the solar effect on climate by the WGK-h explain why paleoclimatologists only detect the outsized climatic effect of SGM on climate. It is expected from theoretical considerations that long uninterrupted periods of low solar activity should have a bigger climate effect than long periods of intermittent activity. Paleoclimatological observations confirm this expectation, supporting that the climatic effect of solar activity is real.

5.6 The Cycle-length/Climate-effect paradox

One of the main objections to a more substantive role on climate change by the sun is that the 11-year solar cycle does not appear to have a great effect on climate. Modern climate analysis using satellite data since 1979 have covered almost four full solar cycles, and it is clear that the changes observed, although significant, are modest (Lean 2017; see Fig. 2.2). And no change is clear between cycles, much less a trend in any climate variable that would correlate to the trend in solar activity.

But solar activity also displays longer cycles. Solar cycles receive the name of important solar researchers. The 11-yr Schwabe cycle, the 22-yr Hale cycle, the 100-yr Feynman cycle, the 200-yr de Vries cycle, the 1000-yr Eddy cycle, and the 2500-yr Bray cycle have all been described in the scientific literature as having a climatic effect (see Vinós 2022, and references within). The 100-yr Feynman cycle is responsible for two 11-yr cycles with low activity in the early 1800s (cycles 5 & 6, 1798–1823), the early 1900s (cycles 14 & 15, 1902-1923) and the early 2000s (cycles 24 & 25, since 2008 and until c. 2030). The 200-yr de Vries cycle is responsible for the spacing of the Wolf, Spörer, and Maunder grand minima during the LIA. The 1000-yr Eddy cycle is responsible for the main climatic periods for the past 2000 years, the Roman Warm Period, the Dark Ages cold period (also known as the Late Antiquity Little Ice Age), the Medieval Warm Period, the LIA, and the Modern warm period that started c. 1850, with some anthropogenic contribution during the past seven decades.

From paleoclimatic studies the longer the solar cycle, the more profound its climatic effect. The biggest effect comes from the 2500-yr Bray cycle, the longest clearly discernible cycle in solar and climatic studies. This cycle, presented in Part II (Sect. 2.2), and Fig. 2.1, not only established the biological subdivisions of the Holocene (the Boreal, Atlantic, Sub-Boreal, and Sub-Atlantic periods), but also caused great periodic fluctuations in human populations of the past. As Bevan et al. (2017) say:

“We demonstrate multiple instances of human population downturn over the Holocene that coincide with periodic episodes of reduced solar activity and climate reorganization. … This evidence collectively suggests quasi-periodic solar forcing of atmospheric and oceanic circulation with wider climatic consequences.”

Those periodic episodes of human population downturn correspond in great part to the 2500-yr Bray cycle, as can be appreciated in Fig. 2.1 or in their figure 3. One can only imagine the kind of climatic effect of the 2500-yr Bray cycle to cause such downturns in human population.

It appears paradoxical that solar variability has almost no effect on the short term (the 11-year cycle), but a huge effect on the long term (the 2500-yr cycle). The WGK-h also provides an explanation for this cycle-length/climate-effect paradox. As shown in Fig. 5.3, solar activity is not the only modulator of MT. At least the QBO, ENSO, the stadium-wave oscillation, and volcanic eruptions act as modulators of MT, and therefore the effect on a particular year can be the opposite of what solar activity alone could dictate. On top of that during an average activity 11-yr solar cycle close to half of the years act in one direction and close to the other half in the opposite direction. The result is a moderate effect where causality is unclear.

The effect of the QBO and ENSO tends toward an average of nearly zero in a few years, and the multidecadal oscillation in a few decades. The longer the solar cycle the longer the period with low solar activity at its troughs. As we have seen, the biggest climatic effect is produced by continuous periods of decades when most of the years display low solar activity. The small increment in the large amount of energy that the planet loses at each winter pole during low solar years is cumulative, as with the increased energy retained by the rise in CO₂. Progressively the planet loses more energy that it gains, and cools down. The longer the cycle, the longer the downturn, and the more profound the cooling. The areas in the MT main paths, particularly the North Atlantic region (including Europe and North America) cool first, longer, and more profoundly, but the energy drain affects the entire planet. And although the Arctic region initially warms due to a larger influx of energy from the enhanced MT, it eventually cools too, as the entire planet gets colder.

Climate is therefore not very sensitive to solar activity until several consecutive 11-yr cycles of consistently low or high solar activity cause the effect to raise above background noise. And then only if the multidecadal stadium-wave oscillation is not acting on MT in the opposite direction. Solar activity and the stadium-wave cooperated during the 1976–1997 climate phase to produce accelerated warming through a strong reduction in MT, that resulted in a long period of global wind stilling (McVicar & Roderik 2010; Zeng et al. 2019) for which no explanation has been provided until now. Since 1998 MT has increased, producing Arctic warming and a pause in global warming. The concatenation of two consecutive low solar activity cycles since 2008 and the approaching shift in the stadium-wave towards an AMO cooling phase, signaled by the recent cooling of the North Atlantic warming hole (46°N–62°N & 46°W–20°W; Latif et al. 2022), spells trouble for the CO₂-hypothesis of climate change. The CO₂ hypothesis projects accelerating warming for as long as atmospheric CO₂ keeps rising. But natural climate change is cyclical, and the modern theory of climate change does not understand that.

In this part of the series, we have seen how changes in solar activity produce changes in climate by modulating the MT of energy towards the poles in a seasonally dependent manner. The result is that the Modern Solar Maximum has significantly contributed to modern global warming, and the current extended solar minimum is at least partially responsible for the ongoing reduced rate of global warming. But the sun’s role as a modulator of poleward energy transport cannot be deduced from first principles. The stratospheric ozone response to UV changes affects MT via the Charney-Drazin criterion, the Holton-Tan effect, and stratospheric-tropospheric coupling. All these atmospheric phenomena derive from observations, not theory. The IPCC considers that solar variability slightly affects climate through small changes in total incoming energy. The top-down mechanism acts through small UV changes that involve even less energy. The change in UV energy, transferred to stratospheric ozone, is partly converted to changes in wind speed. The energy to alter stratospheric circulation dynamics and, through coupling, tropospheric circulation is provided by atmospheric waves generated in the troposphere, not by incoming radiation from the sun. The WGK-h proposes that the energy that alters the climate as a response to solar changes is energy already in the climate system. Under low solar activity this energy is directed to the poles and radiated to space, cooling the planet, and under high activity it remains within the climate system longer, warming the planet. This unexpected energy bypass, that cannot be deduced from theory, is what made the solar-climate question unsolvable for so long. In the last part we will review the evidence that MT is the true climate control knob, and how it can explain the climate changes that have taken place on the planet from the early Eocene hothouse, 52 million years ago, to the present icehouse.

Authored by Javier Vinós & Andy May and originally published at Climate Etc. on August 28, 2022.

Andy May is a Member of the CO2 Coalition. He is a petrophysicist, paleoclimate expert, and author of four books on climate and Kansas history. His latest book is The Great Climate Debate: Karoly vs. Happer.