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The climate dynamics of total solar variability
Richard Mackey Canberra Australia
14 September 2007
There is abundant evidence and general agreement within the scientific community that solar variability of all types irradiance, matter, electromagnetic and gravitational force and shape and the interactions between all five play a key role in the Earth’s climate dynamics.1
In addition to solar variability, there are four other factors, quite independent of solar variability, for which there is evidence that they, too, play a key role in the Earth’s climate dynamics. One is the production of greenhouse gases (water vapour, Carbon Dioxide and methane) (IPCC 2007). Another is the massive re engineering of the planet over the last three hundred years (Cotton and Pielke 2007). A third is the increase in atmospheric pollution that has occurred at the same time as the re engineering of the planet. Volcanoes and earthquakes have also been shown to affect climate dynamics. The fourth is two key natural processes internal to the climate system. One is the stochastic development of natural systems; the second is the interaction between, or phase synchronisation of, the many oscillating natural systems of which the climate is composed.
This paper examines the range and type of climate dynamics arising from total solar variability; it does not address the other factors, except volcanoes and earthquakes to the extent that they might be generated by solar variability.
On August 16, 2006 astronomers at the Synoptic Optical Long-term Investigations of the Sun (SOLIS) facility in the United States reported that Sunspot Cycle No. 24 (SC24) began on July 23, 2006.2 There is some dispute that SOLIS detected the beginning of SC24. We are currently in period of solar minimum between the end of SC23 and the beginning of SC24, which is now expected to begin sometime between mid 2007 and mid 2008.
The amplitude and shape of SC24 could be decisive about the extent to which global warming is the result of total solar variability or human activity. In view of the significance of SC24, in October 2006 NASA appointed a panel of world experts to advise the US Government about the development of SC24.3 The Solar Cycle 24 Prediction Panel anticipates the solar minimum marking the onset of Cycle 24 will occur in March, 2008 (±6 months). If SC24 has a low amplitude and if the overall shape of the cycle is that of a flattened bell shaped curve, it will most likely mean that SC24 will be the harbinger of three decades of global cooling to come and at least five years more drought in Australia.
The eminent Australian scientist, Rhodes Fairbridge, who died in November 2006, aged 92, and who has a special Australian connection, published extensively about the theory that the Earth’s climate dynamics is largely the consequence of total solar variability. Attachment 1 provides an account of the life and science of Rhodes W Fairbridge.
The Sun’s role in climate dynamics
The impact of the Sun on the Earth’s climate has been an active area of scientific inquiry ever since Sir William Herschel presented a series of papers on the subject to the Royal Society in London in 1801. He hypothesised a relationship between solar activity and the 562 year time series of wheat prices (from 1202 to 1764) in Adam Smith’s The Wealth of Nations that was published twenty five years earlier in 1776. See Attachment 2 Sir William Herschel and the Royal Society.
Research published in the last five years shows that the Sun has had a much greater role in generating climate change from the last century to the present time than previously considered possible. This research has also documented the considerable evidence that solar variability has been the key driver of climate change in the past.
Solanki and Krivova (2003a) and (2003b) found that the Sun has been more active in the last seventy years than at any time for over 8,000 years. Whilst this indicates that the high level of solar activity in recent years is exceptional, it is not unique on the multi-millennial time scale. Solanki et al (2004) found that during the last 11,400 years, the Sun spent only 10 percent of the time at a similarly high level of activity.
That the modern high level of solar activity is unusual has been confirmed for the last 7000 years by an analysis of the new reconstruction of the palaeomagnetic dipole moment by Korte and Constable (2005). Usoskin, Solanki and Korte (2006) found that according to this reconstruction, the Sun was in a strongly active state, similar to the modern high activity episode with the decadal sunspot number systematically exceeding 70, only about 3% of the time during the last 7000 years.
Solanki et al (2004) and (2005) and Solanki and Krivova (2004a) and (2004b) reported that most of the warming of the twentieth century has occurred during two periods, from about 1910 to the mid 1940s and from the mid 1970s onwards.
Rozelot and Lefebvre (2006) found that solar irradiance variability accounted for a significant proportion of the trend in global temperatures in the periods 1856–1910, 1910–1945 and 1946–1975.
Scafetta and West (2006a and 2006c) estimated that the increase of solar irradiance during the 20th century might be responsible of approximately 50% of the global warming. However, they report that this contribution was not uniform during the century. Scafetta and West (2006a and 2006c) found that the sun might have contributed 75% of the global warming during the first half of the century (1900-1950) but only 30% during the second half of the century (1950-2000). Their findings confirm that the Sun played a dominant role in climate change in the early past, as several empirical studies had also found. Willson and Mordvinov (2003) reported that the analysis of the data about sunspot activity provided by six overlapping satellite observations since 1978 shows that total solar radiation output had increased by approximately 0.05 per cent per decade.
Labitzke (2006) reviewed many relevant and recent reports of research published in the scientific literature.
In her overview, she notes:
The relatively weak, direct radiative forcing of the solar cycle in the upper stratosphere can lead to a large indirect dynamical response in the lower atmosphere through the modulation of the polar night jet as well as through a change in the Brewer Dobson Circulation.
She explained further that:
Until recently it was generally doubted that the solar variability in the 11 year sunspot cycle (SSC), as measured by satellites, has a significant influence on weather and climate variations. Bur several studies, both empirical and modelling, have in recent years pointed to probable and certain influences. Different observations indicate that the mean meridional circulation systems, like the Brewer-Dobson Circulation and the Hadley Circulation are influenced by the 11 year solar cycle. Today, there is general agreement that the direct influence of the changes in the Ultra Violet part of the spectrum (6% to 8% between solar maxima and solar minima) leads to more Ozone and warming in the upper stratosphere (around 60 km) in solar maxima. This lead to changes in the thermal gradients and thus in the wind systems, which in turn lead to changes in the vertical propagation of the planetary waves that drive the global circulation.
Her own research published over a twenty year period shows that the Quasi Biennial Oscillation is regulated by variable solar activity and that the Sun influences the intensity of the Artic Oscillation in the stratosphere in winter.
This continuing increase in solar output since the 1850s has warmed the oceans, releasing Carbon Dioxide and water vapour.
The time series of total solar variability, like those of climate variability, are non stationary, in that the measures within each are interrelated, and non linear. When analysed using a statistical methodology specially designed to analyse non stationary and non linear data, the role of the Sun in regulating the climate is shown clearly and at statistically significant levels. Empirical Mode Decomposition (EMD) is such a statistical methodology (Huang et al (1998)). EMD, unlike most statistical methodologies for analysing time series, makes no assumptions about the linearity or stationarity of a time series. EMD lets the data speak more directly, revealing its intrinsic functional structure more clearly. It does not does not have the restrictive assumptions of linearity and stationarity that the familiar Fourier-based techniques have, because it uses Hilbert, not Fourier, transforms.
Using EMD, Coughlin and Tung (2005, 2004a, 2004b and 2001), found that the atmosphere warms during the solar maximum and cools during solar minimum almost everywhere over the planet. The statistically significant correlation with the solar flux is positive everywhere over the globe does imply that, on average, the temperatures increase during solar maxima and decrease with solar minima at all latitudes. Coughlin and Tung (2005, 2004a, 2004b and 2001) also found two underlying nonlinear trends over the last four decades. One is the warming of troposphere; the other is the cooling of the stratosphere.
Ruzmaikin, Feynman and Yung (2006) used EMD to analyse the historic time series annual records of the water level of the Nile collected in 622 1470 A.D. (This famous time series is discussed below on page 33). They found the longer solar periodicities of about 88 years and one around 200 years. These are characteristic solar periodicities. For example, they are present in the number of auroras reported per decade in the Northern Hemisphere at the same time. They found the 11-year solar cycle in the Nile’s high-water level variations, but less prominent in the low-water anomalies. Ruzmaikin, Feynman and Yung (2006) explained that the phenomena they report would arise from the influence of solar variability on the atmospheric Northern Hemisphere Annular Mode (NAM). Solar Ultra-Violet variations act in the stratosphere to modulate the NAM. Furthermore, the NAM’s sea level manifestation (the North Atlantic Oscillation) affects the air circulation over Atlantic and the Indian Oceans during high levels of solar activity. Variations of this air circulation influence rainfall in eastern equatorial Africa at the Nile sources. At high solar activity, the air is descending there and conditions are drier, with the opposite effect occurring at low solar activity.
Camp and Tung (2007a and 2007b) established for the first time by direct measurement that the Sun heats the Earth directly.4 They obtained a statistically significant global warming signal of almost 0.2°K due to the 11 year solar cycle.
Camp and Tung (2007a and 2007b) also revealed the surface pattern of warming caused by the Sun. Amongst other things, polar amplification is shown clearly with the largest warming in the Arctic (treble that of the global mean), followed by that of the Antarctic (double). Surprisingly, the warming over the polar region occurs during late winter and spring.
The warming is also larger over continents than over the oceans. In the mid latitudes, there is more warming over the continents than over the oceans. Most of Europe is warmed by 0.5°K and eastern Canada by 0.7°K, while western U.S. sees a smaller warming of 0.4 0.5°K. Iraq, Iran and Pakistan are warmer by 0.7°K and Northern Africa by 0.5°K. The South American Andes is colder by 0.7°K.
They derived a statistically significant measure of the range climate sensitivity (of 2.3°K to 4.1°K) to the variations in the 11 year solar cycle. It is independent of climate models as it is the result of direct measurement. The climate sensitivity lower bound is equivalent to a global warming of 2.3°K at doubled Carbon Dioxide.
Salby and Callaghan (2006) established that there is a decadal oscillation in the tropical troposphere tat depends on the 11-year oscillation of solar irradiance. They found this occurred over the four solar cycles analysed. The statistical analysis achieved higher levels of statistical significance tat had been previously required.
Some of the research about Sun climate connections published in the 1970s and before lacked statistical rigour. As a result, some scientists published explanations of the Earth’s climate dynamics in terms of solar variables that did not stand up to statistical rigour (Pittock 1978, 1983). In addition, sometimes some scientists published claims for a significant role of the Sun in inducing major climate change that could not be sustained when subject to rigorous statistical and methodological scrutiny (Damon and Laut (2004), Laut (2003).
Bond et al (2001) demonstrated that:
The Earth’s climate system is highly sensitive to extremely weak perturbations in the Sun’s energy output, not just on the decadal scales that have been investigated previously, but also on the centennial and millennial time scales documented here.
Furthermore, the authors concluded:
Our findings support the presumption that solar variability will continue to influence climate in the future, which up to now has been based on extrapolation of evidence from only the last 1,000 years.
Bond et al (2001) tested the solar-climate connection by comparing high-resolution measurements of drift ice in three North Atlantic deep-sea cores with proxies of changes in solar irradiance through the entire Holocene. Their analyses imply the footprint of the solar impact on climate extended from polar to tropical latitudes. Amongst other things, the authors found five episodes of markedly reduced rainfall at times of very weak solar minima centered on 6 300, 7 400, 8 300, 900 and 9 500 years ago. Their analyses imply that at times of reduced solar irradiance, the downward-propagating effects triggered by changes in stratospheric Ozone lead to a cooling of the high northern latitude atmosphere, a slight downward shift of the northern tropical jet, and a decrease in the Northern Hadley circulation.
Haigh (2006) reviewed many recently published papers about solar influence on the atmosphere. She concludes:
Multiple regression analysis of zonal mean temperature records from the forty year reanalysis datasets produced by the US National Center for Environment Prediction and the European Center for Medium-Range Weather Forecasts has revealed a detectable 11-year solar signal in the troposphere. These show bands of warming in the mid-latitudes when the Sun is more active suggesting a latitudinal widening of the Hadley cells. Careful analysis of upper air data dating back eighty years has broadly confirmed these findings. Furthermore, the patterns identified are similar to those predicted by atmospheric GCMs for the influence of enhanced solar UV, thus tending to confirm the existence of such an influence of the Sun on the climate.
Bronnimann et al (2006) concluded that studies based on data from the past 25 45 years show that irradiance changes related to the 11 year solar cycle affect the circulation of the upper troposphere in the subtropics and mid latitudes.
More generally, they concluded:5
Our analysis of the relation between solar irradiance variability and zonal mean geopotential height at midlatitudes during the past 82 years reveals an 11 year signal (increasing geopotential height with increasing solar variability) that is consistent with previous studies based on much shorter periods.
Bronnimann et al (2006) reported that while solar impact on climate is increasingly well accepted in the scientific community, the processes that produce it are not.
Stager, Ruzmaikin et al (2007) concluded that there is no doubt that solar irradiance plays a central role in establishing the rhythm of diurnal, seasonal, and orbital-scale climate cycles. They reported that solar irradiance drives convection and migrations of the Intertropical Convergence Zone. They showed that significant relationships between the solar cycle and rainfall existed in East Africa during the 20th century. Stager, Ruzmaikin et al (2007) demonstrated how sunspot cycles could be used to predict positive regional rainfall anomalies several years in advance. They recommended that this knowledge be used to improve the circumstances of people, having regard to the serious consequences that heavy rains in East Africa have for soil erosion, hydropower generation, flooding, and insect-borne disease, and that they can also affect regions farther north that respond to the ebb and flow of the Nile.
Feynman (2007) reported that
There are now many empirical and modelling studies that demonstrate that changes in the solar output are associated with widespread changes in climate. The development of quantitative models and a physical understanding of all the underlying mechanisms involved is currently a rapidly developing field of study. There is considerable evidence that climate variations in response to low frequency solar variations have had major effects on cultures during the last 1,500 years.
Lockwood and Frohlich (2007) asserted that even though the Sun’s regulation of the climate in the past has been established, the warming that the Earth has experienced since the mid 1980s could not be attributed to the Sun. See Attachment 3 “Recent oppositely directed trends in solar climate forcings and the global mean surface air temperature” by Mike Lockwood and Claus Frohlich in Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences June 2007.
Haigh (2007) reviewed some of the evidence for a solar influence on the lower atmosphere. She discussed some of the processes by which the Sun may produce more significant impacts than might be surmised from a consideration only of variations in total solar irradiance. Her paper is published in a new on line peer reviewed scientific journal, Living Reviews of Solar Physics, which enables the paper to evolve as others contribute new material or engage in additional analyses of her commentary. Her paper is a good example of careful science in which analyses and findings are presented with the understatement of cautious science working to the high standards of the exact sciences such as Physics.
Haigh (2007) reviewed some of the science summarised in this paper, but in much more detail. She also surveyed many papers not cited in this paper. She presented many tentative findings throughout her paper including the following:
There is statistical evidence for solar influence on various meteorological parameters on all timescales, although extracting the signal from the noise in a naturally highly variable system remains a key problem. With regard to the climate, further data-mining and analysis are required to firmly establish the magnitude, geographical distribution and seasonality of its response to various forms of solar activity.
In the following sections, a framework for examining how all types of solar activity, not merely irradiance, affect climate. It is based on the ideas of Rhodes Fairbridge. This framework is used to present an outline of the main processes by means of which solar activity of all types produces climate change over a wide spread of time frames and in many different ways in relation to latitude, longitude and altitude (see Attachment 4 for more details).
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