By Andy May
Javier has posted three new essays on the Bray climate and solar cycle on Judith Curry’s web site. Part A is here, part B is here and Part C is here. In these posts, he lays out the evidence, in some detail, for the climate cycle and the associated solar cycle. Here I will summarize the results of his analysis and explain why it matters. The Bray solar and climate cycle are arguably the most important climate/solar cycle of the Holocene Epoch.
The Bray cycle is about 2450 years from beginning to end and the Bray Lows, which are the coldest portion of the cycle, are the most important events. The Bray lows are easily seen in glacial advances around the world (Bray, 1968), foraminifera fossil records, archaeological records, and lake sediment records. They are less evident in ice core records from Greenland and Antarctica. Figure 1 shows the Bray Lows of the Holocene as blue bars, labeled B5 to B1.
The yellow bars are some of the Eddy cycle lows (~980 years). The black rectangles show the location of major grand solar minima clusters (GSM). We call the warm period from 8000 BC to 3500BC the Holocene Climatic Optimum and the cooling period from 3500 BC to the end of the Little Ice Age (LIA) in the late 19th century the Neoglacial. The blue curve on the plot is my global Holocene temperature reconstruction (see here) and the gray curve is a Holocene Greenland temperature reconstruction described in Kobashi, et al., 2017.
Figure 2 (Sunspot reconstruction source: Solanki, et al., 2004)
Figure 2 is the Holocene sunspot reconstruction published in Nature by Solanki, et al. in 2004. Besides the sunspot records there are other data supporting a 2450-year solar cycle that are in phase with the 2450-year climate cycle. The radiocarbon evidence is discussed in Vasiliev and Dergachev (2001) and O’Brien, et al. (1995) discuss the ice core evidence for the cycle. Other evidence is discussed here. The Bray lows in figure 2 are the same as those in figure 1, but the bars are smaller to allow all the Eddy cycle lows to be displayed. The more severe colder periods with extended periods of minimal solar activity occur when Bray lows and Eddy lows occur at about the same time. However, the sun is not the only natural cause of climate change. Ocean cycles or oscillations, often called “natural variability” can occur on millennial time scales as well. The evidence for these long-term oscillations is discussed in Debret, et al. (2009).
The 20th century had an above average number of sunspots, suggesting an above average level of solar activity, certainly higher than the Little Ice Age. Solanki and Krivova (2003) looked at the influence of TSI (total solar irradiance), total UV solar irradiance, and cosmic ray flux on the Earth’s climate. They concluded that if only these three solar influences affect our climate that the sun could have caused the global warming until 1970, but from 1970 to 2000 the sun probably contributed less than 30% of the warming using a conservative solar reconstruction by Frohlich and Lean (1998). Using a different reconstruction by Willson (1997), the sun may have contributed as much as 50% of the warming. Even though we now have satellite measurements of solar radiation variability, these records are inconsistent with one another leading to multiple reasonable interpretations of long-term and short-term trends in TSI and solar activity. Thus, estimates of solar forcing and the impact of the sun on our climate vary from 30% to nearly 100%, see the discussion on this topic here. All we really know is that solar activity is high today and increased during the 20th century, thus it probably contributed to the recent warming, but the amount of the contribution is still unknown.
As Javier writes:
“Given the strength of the correlation between past cycles of climate change, and cycles in the production and deposition of cosmogenic isotopes, like the Bray cycle, the solar-climate relationship is accepted in paleoclimatology as non-controversial. Sixteen of twenty-eight (57%) of the articles whose climatic evidence has been reviewed here explicitly state that changes in solar forcing are likely to be the cause of the observed climatic changes, and only one explicitly rules them out. Then, why is the solar-climate relationship so controversial outside of the paleoclimatology field?”
There are two main reasons given by Javier’s opponents for why they think solar variability cannot be important in climate change. The first is that the cosmogenic isotopes, 14C and 10Be, used as a proxy for solar activity in pre-instrumental times, are, themselves, affected by climate. Therefore, it is stated, that they are invalid as solar proxies and cannot be compared to a climatic record. But, this criticism does not explain why the proxies compare so well to sunspot records over the past 400 years (see figure 3). The climate of the last 400 years is highly variable and yet 14C and 10Be compare extremely well to the sunspot record. Another way to test the validity of 14C and 10Be is to compare their records to auroral records which are related to solar activity, but not to climate. Here we also see excellent agreement. In figure three, from Javier’s essay, auroral frequency is plotted in 3b and the cosmogenic isotope solar modulation function is plotted in 3a and both are compared to the International Sunspot Record in black and the Hoyt and Schatten sun-spot number in gray in 3c. The pink bars identify de Vries lows (spaced at 210 years) and the gray bars identify grand solar minima. The grand solar minima are labeled with their names. The de Vries 210-year solar cycle is modulated by the Bray cycle such that it is more severe in Bray lows (Hood and Jirikowic, 1990) like the Little Ice Age. If the Bray cycle were of terrestrial origin, then we should not be able to see it modulate the solar de Vries cycle in solar records, but we do see it in figure 3 in the sunspot record and in the auroral frequency record.
Figure 3 (source: Javier, here)
Many researchers have identified a climate cycle or oscillation of about 1500 years (Kern et al., 2012 and Darby, et al. 2012), but it does not show up in cosmogenic records. If the cosmogenic isotopes are reflecting terrestrial climate, as opposed to solar activity, why do they not show the 1500-year climate cycle that most believe is related to ocean oscillations? It is difficult to argue that the climate is contaminating some cosmogenic isotope records, but not others.
The second common objection is that observations of our sun show it to be extraordinarily constant, with the total solar irradiation (TSI) varying over a small and insignificant range every 11 years. This conclusion assumes that any solar climatic effect must be due to changes in TSI and the critics claim there is no evidence for this, thus, they conclude the sun has no impact on climate change. As Javier points out this is a non-sequitur fallacy. There is evidence that the sun is the cause of the Bray cycle, if the mechanism is not a change in TSI, it could be a change in UV radiation, which can vary as much as 100% in one 11-year solar cycle, or some other solar cause such as variability in the Sun’s magnetic field strength.
Solar UV radiation helps create ozone and affects the temperature profile in the stratosphere. Thus, variations in solar UV can change the stratospheric temperature profile and density. The density changes change stratospheric pressure and the geopotential height of the tropopause. Ozone is not distributed equally around the world and the distribution can affect surface weather patterns (Labitzke, 2001). There are also other solar changes that might affect climate, such as the solar magnetic field strength, but we will not discuss these mechanisms here.
Another problem with the assertion that solar activity variability is insignificant is that the long-term sunspot record strongly suggests that there is a secular long-term trend of increasing solar activity as we come out of the Little Ice Age. The Bray cycle modulates the ~210-year de Vries cycle as can be seen in Figure 4. The amplitude of the Gleissberg centennial cycle (~103 years, Tan, 2011) and its half-way point are shown by the orange line. This cycle is also shown by the red curve, which increases from left to right. The ~210-year de Vries cycle lows (also increasing from left to right) are shown in blue. Since solar activity, during the de Vries lows and the centennial lows, is increasing with time, the de Vries lows become less noticeable. The increased activity in the lows makes them harder to detect. Thus, it is expected that the next de Vries low, around 2100, will be barely noticed.
This modulation of the shorter cycles might have created a secular warming trend coming out of the Little Ice Age. This long-term trend is not accounted for in current climate models, thus the impact of the trend, if any, is assigned, erroneously, to human influence.
Figure 4 (source: Javier, here)
I’ve prepared a poster, meant to be printed on 11″x17″ or A3 paper that contains much of the information in the first four figures for the entire Holocene. Click on figure 5 below to download it.
Figure 5 (link to download poster, prints best on 11″x17″ or A3 paper and larger)
The top graph in figure 5 is my Northern Hemisphere temperature reconstruction (see here). The second graph is a plot of a Holocene sunspot reconstruction by Solanki, et al. (2017), overlain with the Bray and Eddy cycle lows and the grand solar minima. The third graph shows my global reconstruction (see here) and the Kobashi, et al. (2017) Holocene Greenland reconstruction. I’ve added some historical notes to provide some temporal perspective. Sea level change, satellite temperatures and some surface temperature records are shown along the bottom of the poster.
When the world cools at solar lows, the equator-to-pole-temperature-gradient (EPTG) increases. As the solar minimum approaches, the atmosphere reorganizes as the polar cells expand and the Hadley cells contract. The effect is that the polar temperatures extend farther south (in the Northern Hemisphere, north in the southern hemisphere) and as the cold air moves toward the equator the temperature gradient increases. This does not have to happen in both hemispheres at the same time or with the same severity and, probably, most of the time it doesn’t. The effects on the North Atlantic are particularly severe since the reorganization of the atmosphere causes the NAO (North Atlantic Oscillation) to be in nearly a perpetually negative state due to a weakened polar vortex and an expanding polar cell. Because the cooling does not occur across the globe at the same time or with the same severity, many observers have erroneously concluded that Bray lows are regional and not global.
The connection between solar variability and climate change is so obvious, it is hard to explain why so many scientists deny it. In the 20th century solar activity increased and the sun became very active by historical standards and all direct measurements of the sun’s activity are from this period or later. However, during the Maunder minimum virtually all solar activity stopped and the world became very cold as a result. Javier quotes the following from John Eddy, 1976, this is the last sentence in his 1976 paper in Science entitled “The Maunder Minimum:”
“The reality of the Maunder Minimum and its implications of basic solar change may be but one more defeat in our long and losing battle to keep the sun perfect, or, if not perfect, constant, and if inconstant, regular. Why we think the sun should be any of these when other stars are not is more a question for social [science] than for physical science”
The EPTG defines the state of the world climate on a scale between Extreme Hothouse and Severe Icehouse as can be seen in figure 5 from Javier’s essay, originally from Scotese here. The term Icehouse means a time when a thick permanent icecap cover either the North Pole or the South Pole as we see today. The term hothouse refers to a time when both poles are ice free and tropical plants are growing at both poles.
Figure 6 (source: Scotese, here)
The pole-to-pole temperature curves represent the average global temperatures shown on the right of the figure, currently we are in the severe icehouse state because of the very cold temperatures in Antarctica. We lie between curves 6 and 7 on the left side of figure 6, and today´s global mean temperature is ~ 14.5°C.
Figure 7 (source: Scotese here)
In figure 7, Dr. Christopher Scotese has used available geological evidence to determine the climatic state of the Earth over time. The “normal” climate of the Earth is cooling greenhouse to warming hothouse with an average temperature of about 20°C, at this temperature there are no permanent ice caps and life thrives at the poles. Icehouse conditions, such as we live in today, are relatively rare in Earth’s history and have occurred only four times since complex life evolved in the Cambrian. In these periods, the temperature curve in figure 7 moves into the blue area. The three main cold periods are in the late Ordovician, the late Carboniferous and early Permian, and now. There is a fourth at the end of the Cretaceous, caused by a large bolide impact that ended the Cretaceous, but it was short lived. The cool period at the boundary between the Jurassic and the Cretaceous is not thought to have reached icehouse conditions. Dr. Scotese has shown the impact of a 5°C increase in temperature (the IPCC worst case scenario) from todays temperature (labeled 2016) of 14.5°C at the right end of the graph. As you can see 5°C only takes us back to the Earth’s average temperature for the Phanerozoic. This final point is hypothetical only. It is hard to see, but the preindustrial temperature of 13.8°C is identified in figure 7 as well, recent warming to 14.5°C is hardly noticeable at this scale.
The abbreviations in figure 7 are: PETM – the Paleocene-Eocene Thermal Maximum, EEOC – Early Eocene Climatic Optimum, MECO – Mid-Eocene Climatic Optimum, EOT – Eocene-Oligocene Transition, MMCO – Mid-Miocene Climatic Optimum, LGM – Last Glacial Maximum. The PETM was an unusually warm period 50 million years ago when palm trees grew in the Antarctic and Arctic. During the EOT, the permanent Antarctic ice cap began to grow, it was complete by 12 Mya and expanded dramatically 5 Mya. There was no permanent Arctic ice cap 20 Mya and it grew in fits and starts until reaching a maximum around 19,000 years ago during the last glacial maximum.
The 2450-year Bray climate cycle is linked to a solar cycle of the same length. The cycle is related to wind patterns, changes in ocean currents, precipitation and global average temperature. The cycle appears to act on climate through changes in the stratospheric ozone content and pressures. The stratospheric pressure changes affect Tropospheric weather patterns. Evidence suggests that lows in the Bray cycle cause contraction of the Tropospheric Hadley cells and expansion of the polar cells, increasing the Equator-to-Pole temperature gradient. This results in decreasing global temperatures and changing wind and precipitation patterns. The North Atlantic region is affected most by these changes at Bray lows because they cause the North Atlantic oscillation to enter a persistent negative phase. This intensifies winter climatic effects, explaining why the Little Ice Age was more severe in this region than in the rest of the world.
The world is currently within the Quaternary Ice Age and nearly as cold as it has ever been. The normal average temperature of the world is around 20°C, some 5°C warmer than today. To keep recent warming in perspective, it is important to understand that even if the worse predictions of the IPCC were to occur, we would only be returning to the average temperature of the last 560 million years.