solar cycles

German scientists predict global temperature will decline throughout this century

German scientists contend that two natural cycles will combine to lower global temperatures throughout the 21st Century.

The scientists show that there is an approximate 200-year solar cycle, supported by historical temperature data and proxy data from stalagmites in caves.  “The solar activity agrees well with the terrestrial climate. It clearly shows in particular all historic temperature minima.”

There is also an approximate 65-year cycle of the Atlantic/Pacific oscillation (AMO/PDO) which is well-established by multiple lines of observations.

The 200-year solar cycle has just passed its maximum and will decline during the 21st Century.  It is at least in part responsible for the warming of the last decades of the 20th Century. The AMO/PDO cycle is also beginning its cool phase and will reach a minimum in 2035.

The scientists say that “Non-periodic processes like a warming through the monotonic increase of CO2 in the atmosphere could cause at most 0.1°C to 0.2°C warming for a doubling of the CO2 content, as it is expected for 2100.”  This positive forcing will be overwhelmed by the stronger negative forcing of natural cycles.  They conclude that “the global temperature will drop until 2100 to a value corresponding to the “little ice age” of 1870.”  Read more here.  Below is a graph of historical temperatures and temperature predictions.


This work has been published in two papers:

H.-J. Lüdecke, A. Hempelmann, and C.O. Weiss: Multi-periodic climate dynamics: spectral analysis of long-term instrumental and proxy temperature records, clim. past, 9, 447-452, 2013

F. Steinhilber and J. Beer, Prediction of solar activity for the next 500 years, Jour. Geophys. Res. Space Phys., Vol. 118, 1861-1867 (2013)

Geophysicist predicts new “Little Ice Age” by 2050

Swedish geophysicist Nils-Axel Mörner, in a new peer-reviewed paper, predicts that by the year 2050, we will be experiencing a cold period similar to the “Little Ice Age” that enveloped the world between about 1550 AD and 1850 AD. During that time, global temperatures were up to 2 degrees F colder than now and that chill had a significant effect on food production.

The paper’s abstract reads:

At around 2040-2050 we will be in a new major Solar Minimum. It is to be expected that we will then have a new “Little Ice Age” over the Arctic and NW Europe. The past Solar Minima were linked to a general speeding-up of the Earth’s rate of rotation. This affected the surface currents and southward penetration of Arctic water in the North Atlantic causing “Little Ice Ages” over northwestern Europe and the Arctic.

The contention of the paper is that solar cycles affect ocean circulation in the Arctic and that during solar minima, this change in circulation causes cooling. “Variations in Solar activity lead to changes in the Solar Wind and in Solar irradiance, both of which may affect Earth’s climate. The variations in irradiance are known to be small or even minute. The variations in Solar Wind are large and strong, via the interaction with the Earth’s magnetosphere, it affects Earth’s rate of rotation, by that forcing several different terrestrial variables like the Gulf Stream beat in the North Atlantic.”

Read the 13-page paper here.

Drought in the West

Pima County and the City of Tucson have a cooperative project to study the regional water supply and demand. “The ultimate goal of this effort is to assure a sustainable community water source given continuing pressure on water supply caused by population growth.”

Water is vital to life, so there is concern about the current drought in the Western U.S. and its impact on our water supply. In Arizona, our supply from the Lower Colorado River system stands at just 56% capacity as of Jan. 19, 2010, according to the Bureau of Reclamation. The Salt River system, supplying Phoenix, stands at 79% capacity, and the Verde River system is at 34%.

Some claim that the current drought is the result of human-induced global warming; others blame the ozone hole. However, droughts are naturally occurring and cyclic.

According to NOAA, “Droughts occur throughout North America, and in any given year, at least one region is experiencing drought conditions.” “Droughts similar to the 1950s, in terms of duration and spatial extent, occurred once or twice a century for the past three centuries (for example, during the 1860s, 1820s, 1730s). However, there has not been another drought as extensive and prolonged as the 1930s drought in the past 300 years. Longer records show strong evidence for a drought that appears to have been more severe in some areas of central North America than anything we have experienced in the 20th century, including the 1930s drought.”

In the Pacific northwest, Knapp et al, found that widespread and extreme droughts were concentrated in the 16th and early 17th centuries when the planet was considerably colder than the 20th century.

In a separate study of mean water-year flow on the Columbia River, Gedalof et al. found that “persistent low flows during the 1840s were probably the most severe of the past 250 years,” and that “the drought of the 1930s is probably the second most severe.” They say also that ” recent droughts were not exceptional in the context of the last 250 years and were of shorter duration than many past events.”

In Montana and Idaho, Gray et al. (2004) found that “both single-year and decadal-scale dry events were more severe before 1900,” and that “dry spells in the late thirteenth and sixteenth centuries surpass both the magnitude and duration of any droughts in the Bighorn Basin after 1900.”

Researchers working in the Pyramid Lake area of Nevada found that for the past 2,740 years “intervals between droughts ranged from 80 to 230 years; while drought durations ranged from 20 to 100 years.” Another study in the same area found that the longest of these droughts occurred between 2,500 and 2,000 years ago and between 1,500 and 1,250, 800 and 725, and 600 and 450 years ago, with none recorded in more recent warmer times.

In the Rocky Mountains, Gray et al. (2003) found a pattern of droughts that they say “may ensue from coupling of the cold phase Pacific Decadal Oscillation with the warm phase Atlantic Multidecadal Oscillation.”

Research on the Upper Colorado River Basin shows “a near-centennial return period of extreme drought events in this region.” The major drought of 2000-2004 was not as severe as 1844-1848, and was similar to droughts in the early 1500s and early 1600s. They conclude, “these analyses demonstrate that severe, sustained droughts are a defining feature of Upper Colorado River hydroclimate.” And the results show that more severe droughts are associated with colder cycles.

Work in Arizona and New Mexico shows that “sustained dry periods comparable to the 1950s drought occurred in “the late 1000s, the mid 1100s, 1570-97, 1664-70, the 1740s, the 1770s, and the late 1800s.”

Drought cycles are most closely correlated with various solar cycles of 1,533 years (the Bond cycle), 444 years, 170 years, 146 years, and 88 years (the Gleissberg cycle). Asmerom,et al. report that periods of increased solar radiation correlate with periods of decreased rainfall in the southwestern United States (via changes in the North American monsoon). These solar cycles control the Pacific Decadal Oscillation and the El Nino system which control weather and climate in the southwest. We are just entering solar cycle 24 and it seems very sluggish. That could mean that we will be spared from an intensifying drought.

For specifics on Tucson’s water supply see:

For a primer on drought see:

To understand the proxies used in paleoclimate research see:


Papers reviewed by

Asmerom, Y., Polyak, V., Burns, S. and Rassmussen, J. 2007. Solar forcing of Holocene climate: New insights from a speleothem record, southwestern United States. Geology 35: 1-4.

Benson, L., Kashgarian, M., Rye, R., Lund, S., Paillet, F., Smoot, J., Kester, C., Mensing, S., Meko, D. and Lindstrom, S. 2002. Holocene multidecadal and multicentennial droughts affecting Northern California and Nevada. Quaternary Science Reviews 21: 659-682.

Gedalof, Z., Peterson, D.L. and Mantua, N.J. 2004. Columbia River flow and drought since 1750. Journal of the American Water Resources Association 40: 1579-1592.

Gray, S.T., Betancourt, J.L., Fastie, C.L. and Jackson, S.T. 2003. Patterns and sources of multidecadal oscillations in drought-sensitive tree-ring records from the central and southern Rocky Mountains. Geophysical Research Letters 30: 10.1029/2002GL016154.

Gray, S.T., Fastie, C.L., Jackson, S.T. and Betancourt, J.L. 2004. Tree-ring-based reconstruction of precipitation in the Bighorn Basin, Wyoming, since 1260 A.D. Journal of Climate 17: 3855-3865.

Hidalgo, H.G., Piechota, T.C. and Dracup, J.A. 2000. Alternative principal components regression procedures for dendrohydrologic reconstructions. Water Resources Research 36: 3241-3249.

Knapp, P.A., Grissino-Mayer, H.D. and Soule, P.T. 2002. Climatic regionalization and the spatio-temporal occurrence of extreme single-year drought events (1500-1998) in the interior Pacific Northwest, USA. Quaternary Research 58: 226-233.

Mensing, S.A., Benson, L.V., Kashgarian, M. and Lund, S. 2004. A Holocene pollen record of persistent droughts from Pyramid Lake, Nevada, USA. Quaternary Research 62: 29-38.

Ni, F., Cavazos, T., Hughes, M.K., Comrie, A.C. and Funkhouser, G. 2002. Cool-season precipitation in the southwestern USA since AD 1000: Comparison of linear and nonlinear techniques for reconstruction. International Journal of Climatology 22: 1645-1662.

Woodhouse, C.A., Gray, S.T. and Meko, D.M. 2006. Updated streamflow reconstructions for the Upper Colorado River Basin. Water Resources Research 42: 10.1029/2005WR004455.

Ice Ages and Glacial Epochs

If you have been reading my series on the geological history of Arizona (see Article Index), you may have noticed that the Earth has plunged into an ice age every 145 million years or so. But wait, haven’t ice ages occurred more frequently? No. There is confusion because the term “ice age” is frequently misused by Journalists (and often by many geologists) when they really mean glacial epoch. So what is the difference? An ice age consists of several glacial epochs separated by warmer interglacial periods.

A glacial epoch is a time during which much of the earth’s surface is covered by glaciers. The frequency and duration of glacial epochs are related to the position and orientation of the earth with respect to the sun. The location of the continents also influences the severity of glacial epochs because continents confine ocean currents. For the last 500,000 years of our current ice age, the glacial epoch-interglacial cycle has had a periodicity of 100,000 years. Prior to 500,000 years ago, the glacial-interglacial cycle was 41,000 years. We are now enjoying an interglacial period.

Ice Ages

Our current ice age, called the Pleistocene, started about 2.6 million years ago. Ice ages are related to the position of the solar system within the galaxy. Ice ages have occurred whenever the solar system passes through one of the five known spiral arms of our galaxy, which occurs at intervals of about 145 million years (± 10 million years).

What do stars have to do with ice ages? The hypothesis, greatly simplified is this: Star density within the spiral galactic arms is much greater than in the galactic disk, hence, the flux of cosmic rays is much greater. Cosmic rays penetrating our atmosphere collide with molecules in the air and produce ionization. The ionized particles attract water and produce more clouds than normal. The clouds reflect sunlight which causes cooling. There is both observational and experimental evidence to support this hypothesis. Cosmic ray flux can be deduced from the so-called cosmogenic nuclides, such as beryllium-10, carbon-14, and chlorine-36, as measured in ancient sediments, trees, shells, and in meteorites. The geologic reconstruction of temperature is based on oxygen-18 isotopes from fossils and cave stalagmites. Also, glaciation leaves distinctive deposits and land-forms.

In the graph below, the top panel shows several calculated cosmic ray flux reconstructions. In the bottom panel, that curve is flipped to represent the cooling effect. Notice that the cosmic ray flux coincides with the geologic reconstruction of ice ages. (The green “residual” curve represents the mathematical variance between models and observations.)


Glacial Epochs

Glacial epochs within ice ages seem to be controlled by the relationship of the earth to the sun. There are three main variations called Milankovitch cycles (after Serbian geophysicist Milutin Milankoviæ who first calculated the cycles): Orbital Eccentricity, Axial Obliquity, and Precession of the Equinoxes. All these cycles affect the amount and location of sunlight impinging on the earth. The following explanation of the cycles are summarized from The Resilient Earth:

Eccentricity cycle of 100,000 years

Earth’s orbit goes from measurably elliptical to nearly circular in a cycle that takes around 100,000 years. When Earth’s orbital eccentricity is at its peak (~9%), seasonal variation reaches 20-30%. Additionally, a more eccentric orbit will change the length of seasons in each hemisphere by changing the length of time between the vernal and autumnal equinoxes. The variation in eccentricity doesn’t change regularly over time, like a sine wave. This is because Earth’s orbit is affected by the gravitational attraction of the other planets in the solar system.

Where we are now: Earth’s current orbital eccentricity is 0.0167, which is relatively circular. Presently, Earth’s distance from the Sun at perihelion, on January 3rd, is 91 million miles. Earth’s distance from the Sun at aphelion, on July 4th, is 95 million miles. This difference between the aphelion and perihelion causes Earth to receive 7% more solar radiation in January than in July. Currently, Earth’s orbital eccentricity is close to the minimum of its cycle. There is also a weak variation cycle of 413,000 years.

Axial Obliquity cycle of 41,000 years

The second Milankovitch cycle involves changes in obliquity, or tilt, of Earth’s axis which varies on a 41,000 year cycle from 22.1° to 24.5°. The smaller the tilt, the less seasonal variation there is between summer and winter at middle and high latitudes. For small tilt angles, the winters tend to be milder and the summers cooler. Cool summer temperatures are thought more important than cold winters, for the growth of continental ice sheets. This implies that smaller tilt angles lead to more glaciation.  Where we are now: Currently, axial tilt is approximately 23.45 degrees, reduced from 24.50 degrees just a thousand years ago.

Precession cycle of 23,000- 25,800 years

The third cycle is due to precession of the spin axis. As a result of a wobble in Earth’s spin, the orientation of Earth in relation to its orbital position changes. This occurs because Earth, as it spins, bulges slightly at its equator. The equator is not in the same plane as the orbit of Earth and other objects in the solar system. The gravitational attraction of the Sun and the Moon on Earth’s equatorial bulge tries to pull Earth’s spin axis into perpendicular alignment with Earth’s orbital plane. Earth’s rotation is counterclockwise [viewed from above the north pole]; gravitational forces make Earth’s spin axis move clockwise in a circle around its orbital axis. This phenomenon is called precession of the equinoxes because, over time, this backward rotation causes the seasons to shift.

The full cycle of equinox precession takes 25,800 years to complete. Due to the eccentricity cycle, Earth is closest to the Sun in January and farther away in July, but the northern hemisphere is tilted away. Due to precession, the reverse will be true 12,900 years from now. The Northern Hemisphere will experience summer in December and winter in June. The North Star will no longer be Polaris because the axis of Earth’s rotation will be pointing at the star Vega instead.

Individually, each of the three cycles affect insolation patterns. When taken together, they can partially cancel or reinforce each other in complicated ways.

Glacial epochs can be triggered when tilt is small, eccentricity is large, and perihelion, when Earth is closest to Sun, occurs during the Northern Hemisphere’s winter. Perihelion during the Northern Hemisphere winter results in milder winters but cooler summers, conditions that keep snow from melting over the summer. Deglaciation is triggered when perihelion occurs in Northern Hemisphere summer and Earth’s tilt is near its maximum. There are other factors which act to enhance the forcing effects of the cycles. These include various feedback mechanisms such as snow and ice increasing Earth’s albedo, changes in ocean circulation and enhanced greenhouse heating due to increased CO2 and water vapor concentrations.

Solar Cycles

The sun itself goes through cycles of solar intensity and magnetic flux. When the cycles are in a strong phase, the amount of cosmic rays entering the atmosphere is reduced, there are fewer clouds to block the sun, so it is warmer. When solar cycles wane, as is beginning to happen now, more cosmic rays enter the atmosphere and produce more clouds which block the sun, so it becomes cooler.

The number of sunspots (hence magnetic flux) varies on an average cycle of 11 years. There are also 87-year (Gliessberg) and 210-year (DeVriess-Suess) cycles in the amplitude of the 11-year sunspot cycle which combine to form an approximately 1,500-year cycle of warming and cooling. So far, there is no evidence that atmospheric carbon dioxide has anything to do with the cause of ice ages or glacial epochs.  The graph below shows the correlation between temperature and sunspot cycles, and only coincidental correlation with carbon dioxide.



See also: Climate change in perspective, a tutorial for policy makers


Hoffman, D.L. and Simmons, A., 2008, The Resilient Earth, an online book:

Shaviv, N.J., 2003, The spiral structure of the Milky Way, cosmic rays, and ice age epochs on Earth, New Astronomy 8, 39. (link)

Shaviv, N.J., and Veizer, Jan, 2003, Celestial Driver of Phanerozoic Climate, GSA Today, July 2003.

Veizer, Jan, 2005, Celestial Climate Driver: A Perspective from Four Billion Years of the Carbon Cycle, Geoscience Canada, V. 32, no. 1.