These are the muons that vary with changes in the Sun's activity, causing decadal and centuries long cycles of temperature variation. Earth's magnetic field plays almost no role in regulating GCR generated muons. It has been estimated that the total disappearance of Earth's magnetic field would only result in a 3% increase in ground level radiation.351
This new explanation of Earth's climate history is presented for the non-scientist in Henrik Svensmark and Nigel Calder's book, The Chilling Stars. This new work is a severe blow to proponents of the enhanced greenhouse hypothesis and advocates of anthropogenic global warming who have worked so hard to deny solar influence on global climate.
Our Vagabond Sun
The astrophysical explanation for the major ice age periods in Earth's past has been elaborated on by Nir J. Shaviv, Associate Professor of Physics at the Racah Institute of Physics in Israel. Shaviv decided to take a look at data from the distant past, back through time, to the beginning of complex life in the Cambrian Period. On this research he collaborated with Jan Veizer, a researcher at the Institut für Geologie, Mineralogie und Geophysik, Ruhr Universität, in Germany.
Jan Veizer had originally set out to reconstruct the tropical temperature over the past 550 million years because he wanted to find the CO2 fingerprint. It was a disappointment to him that he couldn't quantify the effect of CO2.352 Working together, he and Shaviv found something much more exciting. The results of their study were revealed in a paper published in 2003, entitled “Celestial driver of Phanerozoic climate?” In it they clearly point out the close correlation of CRF with temperature variation.
Their reconstructed record of climate variations during the Phanerozoic, based on climate sensitive sedimentary indicators, shows intervals of tens of millions of years duration characterized by cold and warm episodes, called icehouses and greenhouses, respectively. Superimposed on these are higher-order climate oscillations, such as the waning and waxing of ice sheets during the past million years. These variations can be clearly seen in Illustration 107.
Illustration 107: Phanerozoic climatic indicators and reconstructed CO2 levels. Shaviv & Veizer 2003.
The dark bars across the top of the figure represent ice-house periods, including the great prehistoric ice ages. The lighter shading for the Jurassic-Cretaceous icehouse reflects the fact that true polar ice caps have not been documented for that period. Notice the extremely high prehistoric CO2 levels, with a noticeable dip during the Carboniferous, 300 mya, the time of great coal swamps and giant insects discussed in Chapter (page 57). The rise and fall of temperature, represented here by oxygen isotope ratios (δ18O) from calcite shell deposits, are noticeably out of phase with the variation in CO2 levels (the upper shaded area).
Other information presented include the amount of drifting sea ice and the extent of glaciation. The paleolatitudinal distribution of ice-rafted debris (PIRD), on the right-hand vertical axis, is an indicator of sea ice. Glaciation is indicted by the presence of other glacial deposits (OGD), such as tillite and glacial marine strata. Both sets of histograms are for relative comparison and represent no actual physical values.
The main result of this research is that the variations of the flux, as predicted from the galactic model and as observed from the Iron meteorites, is in sync with the occurrence of ice age epochs on Earth. The agreement is both in period and in phase: The observed period of the occurrence of ice-age epochs on Earth is 145 ± 7 million years, compared with 143 ± 10 million years for the cosmic ray flux variations. The mid-point of the ice age epochs is predicted to lag by 31 ± 8 million years and is observed to lag by 33 ± 20 million years.
Illustration 108 Cosmic Ray Flux and Temperature. Source Shaviv & Veizer 2003.
In short, when the historical temperature pattern was matched against a reconstruction of the cosmic ray intensity, a much better fit was found. A graph revealing the relationship is shown in Illustration 108. The inverse relationship between temperature and CRF is clear; when CRF rises, temperature falls, when CRF drops off, temperature climbs. Their conclusions are concisely stated in this excerpt from the paper:
“One interpretation of the above result could be that the global climate possesses a stabilizing negative feedback. A likely candidate for such a feedback is cloud cover. If so, it would imply that the water cycle is the thermostat of climate dynamics, acting both as a positive (water vapor) and negative (clouds) feedback, with the carbon cycle "piggybacking" on, and being modified by, the water cycle.”
The evidence of correlations between paleoclimate records and solar and cosmic ray activity indicators, suggests that extraterrestrial phenomena are responsible for climatic variability on time scales ranging from days to millennia. Dr. Shaviv's theory is that the movement of the solar system in and out of the spiral arms of the Milky Way galaxy is responsible for changes in the amount of cosmic rays impacting Earth's atmosphere. Quoting again from Shaviv and Veizer, “We find that at least 66% of the variance in the paleotemperature trend could be attributed to CRF variations likely due to solar system passages through the spiral arms of the galaxy.”353
A Grand Tour of the Galaxy
Illustration 109: The solar systems path through the spiral arms of the Milky Way.
The Milky Way galaxy is a barred spiral galaxy with a diameter of about 100,000 light years containing more than 200 billion stars. Besides stars, the galaxy is composed of gaseous interstellar medium that sometimes concentrates into dense gas clouds. These clouds, made up of atoms, molecules, and dust, come from the explosions of older stars and are the source of new ones. All of the matter rotates around the galaxy's central axis. Our Sun resides about two-thirds of the distance from the center of the galaxy to the edge of its disk. Seen from above, we are located in one of the Milky Way's outer spiral arms, known as the Orion Arm.354
Just as Earth orbits the Sun, the Sun and its brood of planets orbit the Milky Way Galaxy's center of mass. The direction of the Sun's path through interstellar space is in the direction of the bright star Vega, near the constellation of Hercules. The solar system's average orbital speed is about 132 miles per second (212 km/sec). The Sun lies 28,000 light years from the Galactic Center, so it completes one revolution every 226 million years.355 Note the relationship of the Sun's orbit to the arms in Illustration 109.
It is thought that the Solar System's location in the galaxy was a factor in the emergence of life on Earth. The Solar System lies well outside the star-crowded environs of the galactic center. If it were closer to the center, the combination of gravitational forces and intense radiation levels might have prevented life from developing on our planet. The solar system's current location in the Orion Arm is not safe from supernovae. Some scientists have hypothesized that recent supernovae may adversely affect life by pummeling Earth with radioactive dust grains and larger bodies.356
The galaxy's spiral arms are home to large concentrations of massive, young blue stars—the type of stars that result in supernovae. The arms themselves are actually density waves rippling through the dust and gas of interstellar space. At the same galactic orbital radius as the Sun, the arms travel at a rotational velocity of 82 miles per second (130 km/sec), about half the velocity of the solar system.357 This difference in velocity, between the solar system and the density waves that form the arms, has given Earth long periods of interstellar stability for life to evolve.
Illustration 110: Differential Rotation caused by differing orbital velocities.
To understand why scientists think the spiral arms are not simply formed by orbiting stars, consider what would happen to the arms if they were. Just as satellites orbiting Earth take different amounts of time to circle the planet, stars or anything else that orbit the galaxy, do so at different rates of speed. This is called differential rotation, and it is the reason that the spiral arms cannot be formed by orbiting stars, dust and gas. The difference in angular speeds of different parts of the galactic disk cause stars closer to the galactic center to complete a greater f
raction of their orbit in a given time (Illustration 110).
Illustration 111: The winding dilemma.
Over billions of years, differential rotation leads to the winding dilemma, first described by Bertil Lindblad in 1925. Though differential rotation provided a ready explanation for the spiral pattern of stars, he realized that a permanent spiral arrangement of stars was untenable. This is because differential rotation is too efficient at making the spiral arms. After only 500 million years, the arms should be so wound up that the spiral structure would disappear (see Illustration 111). Anything left of the spiral pattern would occupy only a small part of the disk. Observations of other galaxies contradicts this: the spiral arms in galaxies rarely have more than two turns. Since galaxies are billions of years old, and the spiral pattern must be a long-lasting feature, some other mechanism must be at work.
One theory says that the spiral structure is a wave that moves through the disk causing the stars and gas to clump up along the wave—a density wave. The spiral arms are where the stars pile up as they orbit the galactic center. The greater density of stars in a spiral region causes greater gravity, which concentrates the stars and gas. The spiral regions rotate about half as fast as the stars move. Stars behind the region are pulled into the region by gravity, at the same time speeding up—almost as though they are hurrying to pass through the dangerous congestion of the arm. Stars leaving the region of greater gravity are pulled backward and slow down (Illustration 112).
Illustration 112: Density wave causing compression and new star formation. After Strobel.
Gas entering a spiral region density wave is compressed, leading to the formation of new stars (page 164). On the downstream side of wave, there are many star formation regions. The star formation region nearest to Earth is an open cluster in the constellation of Taurus called the Pleiades, also known as the Seven Sisters. The cluster is about 12 light years away and is dominated by hot blue stars, thought to have formed within the last 100 million years. The observed bright reflection nebula and dark nebular filaments in the Pleiades indicates they are interacting with a dense molecular cloud.358
There are many stellar nurseries in the solar system's neighborhood. One of the most spectacular star-birth regions is the Orion Nebula, which lies 1,500 light-years away, in the direction of the constellation Orion the Hunter. It is one of the nearest regions of recent star formation, with stars believed to have formed only 300,000 years ago. The nebula is a giant gas cloud illuminated by bright, young stars as shown in Illustration 113. The great plume of gas in the lower left in this picture is the result of the ejection of material from a recently formed star.
Illustration 113: A view of the Orion Nebula, an active stellar nursery. Source NASA/HST
The other popular theory of spiral arm formation depends on shock waves from supernova explosions to shape the spiral pattern. When a supernova shock wave reaches a gas cloud, it compresses the cloud to stimulate the formation of stars. Some of them will be massive enough to produce their own supernova explosions to keep the cycle going. Coupled with the differential rotation of the disk, the shock waves will keep the spiral arms visible. Whatever the mechanism, the spiral arms are areas of elevated cosmic ray radiation, due to the births and subsequent deaths of hot massive stars.
Ice Ages and Spiral Arms
Given the estimated locations of the Milky Way's spiral arms and the difference in rotational velocity between them and the solar system, the Sun should pass through an arm every 134 ± 25 million years on average. This fits rather well with both the fluctuation in cosmic rays and the occurrence of ice ages (page 202).
A record of the long-term variations of the galactic cosmic ray flux can be extracted from Iron meteorites. It was found that the cosmic ray flux varied periodically, with flux variations greater than a factor of 2.5. These variations had an average period of 143 ± 10 million years. This is consistent with the expected spiral arm crossing period and with the theory that the cosmic ray flux should vary.359
Illustration 114: Relationship between meteorite records, cosmic ray flux, ice ages, and spiral arm passage. Source N. Shaviv 2003.
A second area of agreement is in long-term activity. There were no ice age epochs on Earth between 1 and 2 billion years ago. During this same period, it appears that the star formation rate in the Milky way was about half of its average during the past billion years or prior to 2 billion years ago. The correlation is shown in Illustration 114.
Marsh and Svensmark and Shaviv and Veizer are not alone in their conclusions. In 2005, R. G. Harrison and D. B. Stephenson explored the robustness of this chain of events by examining relationships between diffuse solar radiation and cloud amount measured at ten United Kingdom solar radiation-recording sites.360 In the words of Harrison and Stephenson, “our data analysis confirms the existence of a small, yet statistically robust, cosmic ray effect on clouds, that will emerge on long time scales with less variability than the considerable variability of daily cloudiness.”
Shaviv has concluded that Cosmic Ray Flux variations explain more than two-thirds of the variance in the reconstructed temperature, making CRF variability the dominant climate driver over geologic time scales. But we are more interested in shorter periods of change. In particular, what was the effect of cosmic rays on Earth's climate over the past century.
In a 2005 paper on the calculated effects of cosmic ray flux on climate, Shaviv reported, “CRF over the previous century should have contributed a warming of 0.47 ± 0.19°K, while the rest should be mainly attributed to anthropogenic causes. Without any effect of cosmic rays, the increase in solar luminosity would correspond to an increased temperature of 0.16 ± 0.04°K.”361 This is in agreement with empiricist calculations, as discussed in the previous chapter, that indicate CO2 levels account for less than half of the recent temperature rise. In fact, Shaviv's estimate for the contribution of irradiance is less that the commonly attributed 0.25°C.362 If these predictions are correct, CO2 may have contributed only 0.25°C to last century's warming trend.
If correct, this theory implies that we are at the end of a 10 million year long ice age, during which glacial episodes come and go. Gradually, over the next few millions of years, the severity of the glacials should diminish, until they disappear altogether. But, to quote Dr. Shaviv, “I wouldn't buy real estate in Northern Canada just yet.”
A final wrinkle in the story of cosmic rays affecting events on Earth has been reported by researchers from the University of Kansas.363 It had been known for some time that a 62 ± 3 million-year cycle in fossil diversity has persisted over the past 542 million years. There have been efforts to link this cycle to global mass extinctions, but no satisfactory mechanism has been found to explain the phenomenon. Recently, Mikhail V. Medvedev and Adrian L. Melottpropose have proposed that the cycle is caused by modulation of CRF due to the solar system's vertical oscillation in the galaxy, which has a period of around 64 million years.
Much like the Sun and Earth generate shock waves in space, due to their magnetic fields, the Milky Way also generates a shock wave in intergalactic space. The production of cosmic rays that takes place in the galactic halo varies from north to south due to our galaxy's motion toward the Virgo cluster. This new research has shown that CRF can vary by a factor 4.6 and reaches a maximum at the northern-most displacement of the Sun.364
The addition of this 64 million year cycle to the arm transit cycle could increase the complexity of CRF variability. This would be similar to the way eccentricity, obliquity and precession combine to create the Croll-Milankovitch cycles.
Illustration 115: The solar system's wobbly trajectory. Source M. Medvedev, University of Kansas.
When asked by the authors about the impact of Medvedev and Melott's idea on climate, Shaviv said: “Although I haven't checked it, my suspicion with the idea of Medvedev and Melott is that it will not be consistent with the Be isotope ratio age of the cosmic rays... Another point is that there is no notable climate variations
on the 60 Million year time scales.” He added, “Anyway, Medvedev is my friend, we overlapped as post-docs at CITA. Since he is sharp and original, I wouldn't discard his ideas without thoroughly checking them.”365 Clearly, this will be an area of ongoing scientific investigation for some time.
Cosmo-Climatology
This concludes the case for cosmic rays influencing Earth's climate. As we have seen, the same underlying mechanism—regulation of low-level, tropospheric clouds by ionizing radiation caused by cosmic ray generated muons—explains two puzzling climatological questions. These questions are: what causes short term, decadal temperature change, and what causes long-term climate change over millions of years? Regulation by the Sun of 40% of the GCR induced muon showers explains decadal variation where varying solar irradiance cannot. And the solar system's transiting of the spiral arms of the Milky Way galaxy explains why Earth has experienced long warm periods, punctuated by ice ages tens of millions of years long.
If we combine the effects of all the forcings that derive from extraterrestrial sources, we find a compelling set of explanations for climate change during Earth's long history. The forcings and associated time scales are as follows:
Decadal ― cosmic ray muons regulated by the solar cycle. This accounts for temperature variability in sync with the 11 year sunspot cycle.
Hundreds to thousands of years ― Solar regulation of cosmic rays plus changes in solar irradiance. This variability includes historical climate change as witnessed in the Little Ice Age and Medieval Warm Period.
Tens to hundreds of thousands of years ― The Croll-Milankovitch cycles that combine Earth's attitudinal and orbital variations. This variability drives the glacial-interglacial cycles during ice ages.
The Resilient Earth: Science, Global Warming and the Fate of Humanity Page 22
