By Andy May
In part 2 we discussed the IPCC hypothesis of climate change that assumes humans and our greenhouse gas emissions and land use choices are the climate change “control knob.” This hypothesis underpins their attempts to model Earth’s climate. But the model output fails to match many critical observations and in some cases the model/observation mismatches are getting worse with time. Since these mismatches have persisted through six major iterations of the models, it is reasonable to assume the flaw is in the assumptions, that is within the hypothesis itself, as opposed to being in the model construction. In other words, it is likely the IPCC conceptual model should be scrapped, and a new one using different assumptions constructed. In this post we examine their underlying assumption that the Sun has not varied significantly, at least from a climate perspective, over the past 150-170 years.
As well-explained by Bob Irvine, there are only two things that contribute to the thermal energy content of a planet, the amount of incoming energy and the energy residence time within the system. These two things, along with the climate system heat capacity, determine the surface temperature. Arrhenius assumed and the IPCC still assumes the Sun delivers a nearly constant amount of energy to Earth over periods of a few hundred years, constant enough that it has no impact on our climate. In addition, they work with annual averages to avoid seasonal and orbital changes. In AR6, the base period is 1750 to 2019. The IPCC assumes the Sun is invariant, at least on an annual basis, over this period and volcanic activity is just slightly negative, as shown in figure 2. AR6 summarizes their views as follows:
“Changes in solar and volcanic activity are assessed to have together contributed a small change of –0.02 [–0.06 to +0.02] °C since 1750 (medium confidence).”
AR6 p. 962.
The change of “-0.02°C” is indistinguishable from zero. Since the IPCC assumes that solar input to Earth’s climate system does not change, temperature only varies as a function of the “energy residence time,” which they assume is controlled by human activity and greenhouse gas emissions.
As explained in part 2, greenhouse gases absorb radiation emitted by Earth’s surface and use it to warm the lower atmosphere, thus delaying its eventual escape to space. It is uncontroversial that adding more of these gases increases the delay, warming the planet’s surface.
The IPCC assumes that the radiative forcing for a doubling of CO2 from 1750 levels is 3.9 W/m2 or less and that the climate impact of this forcing change is roughly equivalent to a change in solar forcing of 3.9 W/m2. But a 3.9 W/m2 change in greenhouse gas emissions from the atmosphere in the infrared frequencies cannot penetrate the top millimeter of the ocean. Thus, it has a different impact than a 3.9 W/m2 change in solar radiation, part of which penetrates more than 100 meters into the ocean before it is fully absorbed. Oceans cover 70% of Earth’s surface and have a low albedo (reflectivity) to sunlight, thus the oceans absorb most sunlight reaching Earth.
Downwelling greenhouse gas radiation warms the surface of the ocean briefly, then most of it is quickly carried away by the overlying wind or as latent heat of evaporation. It has a short residence time in the ocean and in Earth’s climate system. A change in incoming solar radiation is absorbed deeper in the ocean and has a longer residence time. This increases the ocean warming effect at the point of incidence and spreads the new thermal energy over a larger volume of water. The difference in the surface warming effect can be a factor of three or more, Watt-per-Watt, relative to a change in greenhouse gas back-radiation.
Evidence that Bob Irvine’s hypothesis is correct includes the change in ocean temperatures over the course of one approximately 11-year solar cycle. The shallow ocean heat storage above the 22°C isotherm, increases almost an order of magnitude more than the direct effect of the solar cycle radiation increase. Further, this change is in phase with the solar cycle. Small changes in the Sun’s output can accumulate over time, increasing their effect on total climate system heat storage.
Wigley and Raper calculated that for a change in solar output of about 1.1 W/m2, roughly the change over one solar cycle, the direct change in Earth’s surface temperature should theoretically be in the range of 0.014°C to 0.025°C, which is undetectable. However Judith Lean shows the observed surface temperature change, due to the increase in solar activity is about 0.1°C, 4 to 7 times what is expected and the increase in the upper atmosphere is 0.3°C, more than an order of magnitude more than expected from the change in radiation delivered to Earth.
Lean also adds that were the Sun to become anonymously low, like during the Maunder Solar Grand Minimum (from 1645 to 1715) the expected global surface temperature cooling would still be less than a few tenths of a °C. This is only true if the cooling is linear with the change in radiation and if there are no unexpected amplifiers in the climate system, both assumptions are unlikely. We know that there are amplifiers in the climate system because the warming and cooling over the solar cycle are more than the theoretical change as Wigley and Raper have shown. The warming and cooling could be linear with the change in radiation, but there is no reason to assume this, Earth’s surface is complex and ever changing.
More simply put, we know that the climate system somehow amplifies changes in insolation, but we don’t know exactly how. We know that solar output in the Maunder Solar Grand Minimum was less than now and the change from current solar output is small in percentage terms, but we have no idea what the effect on Earth’s climate of the change was, only that historical records and climate proxies suggest the effect was very large.
Known solar cycles correlate well with known climate cycles and are in phase with them. Various hypotheses have been proposed to show how the Sun’s output changes over time periods of a thousand years or less. These are periods short enough to affect surface temperature from 1750, near the end of the Little Ice Age, to 2019. The problem is that although a correlation between solar activity proxies and climate change can be demonstrated, a mechanism for the change in solar activity cannot. Attempts to explain solar variability by internal changes in the Sun only work in some cases. For example, Frank Stefani and colleagues have shown how the approximately 193-year de Vries solar cycle may be a beat period between the 22.14 Hale Solar Cycle and the 19.86-year orbit of the Sun around the solar system barycenter.
Nicola Scafetta and Antonio Bianchini have shown that the orbits of the planets around the Sun correlate with solar activity proxies. However, exactly how the small gravitational changes influence the solar dynamo is unclear. Thus, the hypothesis that solar activity is regulated within the Sun itself cannot completely reproduce observations, and planetary tidal forces seem too weak to accomplish the changes. These gaps in our knowledge of the mechanisms impede the acceptance that multi-centennial or multi-millennial solar changes can influence our climate. The Sun does change according to accepted solar proxies, like carbon-14 and beryllium-10 records, but the change mechanism is unclear.
The problem with the IPCC (and Arrhenius’) assumptions is that they ignore this empirical and theoretical evidence that solar output and/or solar energy input to the Earth’s climate system varies significantly over periods of a few hundred years. Their obsession with human greenhouse gases has blinded them to possible natural influences on climate change that they should be investigating. This is not to say that human greenhouse gases have no effect, it is likely that they do have some effect, but evidence suggests that natural influences, like the Modern Solar Maximum and ocean oscillations, play a significant role also.
There is a large body of peer-reviewed papers on the subject of solar activity as a climate change driver, yet AR6 ignores most of them. A very comprehensive review of recent research on the effect of the Sun on Earth’s climate is presented in a recent paper by Ronan Connolly and 22 colleagues. In the paper they cite 396 papers on the connection between the Sun and climate, as opposed to only 68 in AR6 WG1, both AR6 WG1 and the paper by Connolly, et al. were first published in 2021. This illustrates how selective the IPCC authors were in what research was considered in their report.
There is no valid reason to assume that the Sun was constant in its effect on Earth’s climate from 1750 until today. The usual reasoning is that observed changes in solar output are too small, in terms of power delivered per square meter (W/m2) relative to changes caused by increasing greenhouse gases, but as Irving explains these two sources of change are not comparable because the frequency content of the two sources are different.
Summary
The goal of this post is not to convince anyone that solar variability is responsible for all or part of modern global warming, a subject that is well covered elsewhere. The point is that the IPCC reports and the CMIP models do not consider or investigate this possibility.
It is true that exactly how solar variability occurs and how it affects climate are not known, but the Sun does vary, and the variations correlate with climate changes. It is unlikely that climate changes are a direct result of the change in insolation, the solar changes are amplified by Earth’s climate system somehow.
We also do not know how much solar output has varied since 1650, the middle of the devastatingly cold Little Ice Age and the onset of the Maunder Solar Grand Minimum. There are several possible reconstructions of solar output since then. Figure 3 shows one of them constructed from an ice core beryllium-10 isotope record by Steinhilber, et al. The major climatic periods since 0AD are noted on it, and the Solar Grand Minima are identified.
The absolute values of delta-TSI (the change in total solar irradiation), in W/m2, plotted in Figure 3 are based on one of many possible modern TSI reconstructions (PMOD) and may not be accurate, but their values relative to one another are reasonable. None of the modern satellite TSI reconstructions are well supported, and the debate over which one is the best is furious and ongoing. See the discussion here for an introduction to the debate. It is best to not consider the absolute value of the Y axis in Figure 3, and consider it a TSI index, no one really knows how much TSI has changed, even over the satellite era. Further, as we’ve seen, how TSI changes relate to climate changes quantitatively is also not known. All we know is that they generally change together.
In Figure 3 we can see that colder periods, like the Little Ice Age, have some solar peaks and some warmer periods, and the Medieval Warm Period has solar lows. None of the climatic periods identified in Figure 3 were uniformly cold or warm. What we call the Little Ice Age, had some hot periods, and the Medieval Warm Period had cold periods (see the section after figure 2 here for references). Further, the correlation between solar activity and climate is not exact, nor is it uniform and synchronous over the whole planet. This is probably because of the effects of convection and atmospheric and oceanic circulation that I examine in the next post. Climate change is complicated.
The beginning and end of the climate periods identified in figure 3 are approximate, and mostly a judgement call. All the climate periods start and end at different times in different places.
However, we do know that some solar proxy reconstructions correlate well with climate proxies since 1850 (see Table 1 here), and that alone is justification for additional research. Solar variability can explain anywhere from zero to almost 100% of the warming since 1850, depending upon the datasets used.
This is a very brief summary of the evidence that changes in solar activity affect climate. More comprehensive discussions of possible mechanisms and the evidence for them are available. Suffice it to say that this is an area of research that is too often ignored and brushed away as unimportant, especially by the IPCC. The sometimes excellent correlations in the peer-reviewed literature between solar activity and climate change alone should be enough to spur research. The fact that the IPCC has ignored these correlations is evidence of bias.
A point we will make many times in this series is that the Earth is not a uniform single thermodynamic body. Its surface is constantly changing. Treating it as a simple thermodynamic body, and one that can be characterized by a global average temperature is a huge mistake. Next, in part 4, we will discuss the potential impact of long-term changes in convection patterns.
Download the bibliography here.
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(Lacis, Hansen, Russell, Oinas, & Jonas, 2013), (Lacis, Schmidt, Rind, & Ruedy, 2010), and (IPCC, 2021, p. 179) ↑
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(McKitrick & Christy, A Test of the Tropical 200- to 300-hPa Warming Rate in Climate Models, Earth and Space Science, 2018), (McKitrick & Christy, 2020), (Lewis, 2023), (IPCC, 2021, p. 990) ↑
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(Irvine, A Thought Experiment; Simplifying the Climate Riddle, 2023) and (Irvine, A comparison of the efficacy of green house gas forcing and solar forcing, 2014) ↑
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(IPCC, 2021, p. 961) ↑
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(IPCC, 2021, p. 925) ↑
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(IPCC, 2021, p. 959), (Hansen, et al., 2005), and (IPCC, 2013, pp. 664-667) ↑
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(Irvine, A Thought Experiment; Simplifying the Climate Riddle, 2023) and (Irvine, A comparison of the efficacy of green house gas forcing and solar forcing, 2014). Irvine provides estimates of the surface warming “efficacy” of greenhouse gas forcing versus solar forcing. ↑
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Also called the Schwabe solar cycle. ↑
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An isotherm is a plane of equal temperature, in this case 22° below the ocean surface. ↑
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(White, Dettinger, & Cayan, 2003). The change in radiation expected ocean temperature change is done with the Stefan-Boltzmann equation. The expected change in heat content assumes a solar cycle radiation change of about 0.1 W/m2. ↑
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(Wigley & Raper, 1990) ↑
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(Lean, 2017) ↑
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https://andymaypetrophysicist.com/2017/09/09/hadcru-power-and-temperature/ ↑
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(Connolly et al., 2021), (Soon W. , et al., 2023), (Scafetta N. , Empirical assessment of the role of the Sun in climate change using balanced multi-proxy solar records., 2023), and (Soon, Connolly, & Connolly, 2015). ↑
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(Behringer, 2010) and (May, Are fossil-fuel CO2 emissions good or bad?, 2022) ↑
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(Scafetta N. , Understanding the role of the sun in climate change, 2023c) and (Scafetta N. , Empirical assessment of the role of the Sun in climate change using balanced multi-proxy solar records., 2023) ↑
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(Connolly, et al., 2023), Table 1 ↑
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(Stefani, Horstmann, Klevs, Mamatsashvili, & Weier, 2023) ↑
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(Scafetta & Bianchini, Overview of the Spectral Coherence between Planetary Resonances and Solar and Climate Oscillations, 2023b) and (Scafetta & Bianchini, The Planetary Theory of Solar Activity Variability: A Review, 2022) ↑
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(Vinós & May, The Sun-Climate Effect: The Winter Gatekeeper Hypothesis (I). The search for a solar signal, 2022) and (Usoskin, Solanki, & Kovaltsov, 2007) ↑
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(Vinós & May, The Winter Gatekeeper hypothesis (VII). A summary and some questions, 2022f), (Wyatt & Peters, A secularly varying hemispheric climate-signal propagation previously detected in instrumental and proxy data not detected in CMIP3 data base, 2012b), (Wyatt, Kravtsov, & Tsonis, Atlantic Multidecadal Oscillation and Northern Hemisphere’s climate variability, 2012a), and (Wyatt & Curry, 2014). ↑
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(Connolly et al., 2021) ↑
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(Soon, Connolly, & Connolly, 2024, p. 60) ↑
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(Connolly et al., 2021), (Soon, Connolly, & Connolly, Re-evaluating the role of solar variability on Northern Hemisphere temperature trends since the 19th century, 2015), (Crok & May, 2023), (Hoyt & Schatten, 1997), and (Haigh, 2011) ↑
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(Connolly, et al., 2023), see Table 1. ↑
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(Connolly et al., 2021) ↑
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(Soon, Connolly, & Connolly, Re-evaluating the role of solar variability on Northern Hemisphere temperature trends since the 19th century, 2015), (Connolly et al., 2021), (Soon W. , et al., 2023), (Vinós, Climate of the Past, Present and Future, A Scientific Debate, 2nd Edition, 2022), (Hoyt & Schatten, 1997), and (Haigh, 2011). ↑
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