Cycles and Cycles

[776281]

Day and night, summer and winter the most obvious of the cycles.

Perihelion and aphelion. The earths orbit around the sun is not quite circular, very slightly eccentric when the earth is closed to the sun that is perihelion, Currently perihelion is about January 4.

The Malinkovich Cycles
http://en.wikipedia.org/wiki/Milankovitch_cycles

The Earth's orbit is an ellipse. The eccentricity is a measure of the departure of this ellipse from circularity. The shape of the Earth's orbit varies from being nearly circular (low eccentricity of 0.005) to being mildly elliptical (high eccentricity of 0.058) and has a mean eccentricity of 0.028. The major component of these variations occurs on a period of 413,000 years (eccentricity variation of ±0.012). A number of other terms vary between components 95,000 and 125,000 years (with a beat period 400 ka), and loosely combine into a 100,000-year cycle (variation of −0.03 to +0.02). The present eccentricity is 0.017.

The angle of the Earth's axial tilt (obliquity) varies with respect to the plane of the Earth's orbit. These slow 2.4° obliquity variations are roughly periodic, taking approximately 41,000 years to shift between a tilt of 22.1° and 24.5° and back again. When the obliquity increases, the amplitude of the seasonal cycle in insolation (INcoming SOLar radiATION) increases, with summers in both hemispheres receiving more radiative flux from the Sun, and the winters less radiative flux.

Precession is the change in the direction of the Earth's axis of rotation relative to the fixed stars, with a period of roughly 26,000 years. This gyroscopic motion is due to the tidal forces exerted by the sun and the moon on the solid Earth, associated with the fact that the Earth is an oblate spheroid shape and not a perfect sphere. The sun and moon contribute roughly equally to this effect.

When the axis is aligned so it points toward the Sun during perihelion, one polar hemisphere will have a greater difference between the seasons while the other hemisphere will have milder seasons. The hemisphere which is in summer at perihelion will receive much of the corresponding increase in solar radiation, but that same hemisphere will be in winter at aphelion and have a colder winter. The other hemisphere will have a relatively warmer winter and cooler summer.

http://en.wikipedia.org/wiki/Milanko...al_inclination

The inclination of Earth's orbit drifts up and down relative to its present orbit with a cycle having a period of about 70,000 years. Milankovitch did not study this three-dimensional movement. This movement is known as "precession of the ecliptic" or "planetary precession".

It has been proposed that a disk of dust and other debris exists in the invariable plane, and this affects the Earth's climate through several possible means. The Earth presently moves through this plane around January 9 and July 9, when there is an increase in radar-detected meteors and meteor-related noctilucent clouds.[2][3]

The Moon affects tides, tides affect climate.
The Moons orbit also varies in eccentricity Preihelion varies significantly over cycle of months. There is also a cylcle of correllation between the new and full moons with perihelion.

So when the new or full moon corresponds with perigee at its closest extent and this corresponds with perihelion we get extreme tides. Theory goes that these extreme tides give greater deepwater mixing and thus we get a cooler period. (Which means we should be freezing this year)

Solar cycle
http://en.wikipedia.org/wiki/Solar_cycle

The solar cycle, or the solar magnetic activity cycle, is the main source of periodic solar variation (changing the level of irradiation experienced on Earth) which drives variations in space weather and to some degree weather on the ground and possibly climate change.[1] The cycle is observed by counting the frequency and placement of sunspots visible on the Sun. Powered by a hydromagnetic dynamo process driven by the inductive action of internal solar flows, the solar cycle:

More to follow

[sinimod]

It would be interesting to know why glacial cycles spontaneously changed from the 41 kyr obliquity cycle to the ~100 kyr eccentricity cycle about 1 ma. To date, I haven't found any explanations.

[776281]

I cannot find why the change. Unless the debris in the solar plane cleared slowly until some threshold was passed. http://en.wikipedia.org/wiki/Yarkovsky_effect

The Yarkovsky effect is a force acting on a rotating body in space caused by the anisotropic emission of thermal photons, which carry momentum. It is usually considered in relation to meteoroids or small asteroids (about 10 cm to 10 km in diameter), as its influence is most significant for these bodies.

http://en.wikipedia.org/wiki/Poyntin...bertson_effect

The Poynting–Robertson effect, also known as Poynting–Robertson drag, named after John Henry Poynting and Howard Percy Robertson, is a process by which solar radiation causes a dust grain in the solar system to slowly spiral inward. The drag is essentially a component of radiation pressure tangential to the grain's motion. The first description of this effect, given by Poynting in 1903, was still "luminiferous aether"-based. Later, in 1937, Robertson described the effect correctly in terms of general relativity.

http://en.wikipedia.org/wiki/Yarkovs...Paddack_effect

The Yarkovsky–O'Keefe–Radzievskii–Paddack effect, or YORP effect for short, is a second-order variation on the Yarkovsky effect which changes the rotation rate of a small body (such as an asteroid). The term was coined by Dr. David P. Rubincam in 2000.

In the 19th century, Yarkovsky realised that the infrared radiation escaping from a body warmed by the Sun carries off momentum as well as heat. Translated into modern physics, each photon escaping carries away a momentum p = E/c where E (=hν) is its energy and c is the speed of light. Radzievskii applied the idea to rotation based on changes in albedo[1] and Paddack and O'Keefe realised that shape was a much more effective means of altering a body's spin rate. Paddack and Rhee suggested that the YORP effect may be the cause of rotational bursting and eventual elimination from the solar system of small asymmetric objects.[2]

This isn't a eureka I have found it idea, more a I cannot find or think of another explanation idea. Furthermore I have no idea how you would demonstrate it.

It is also appears that while the orbital cycles clearly provide the timing of the glacial cycles, they do not explain it. The orbital forcing should barely provide a tickle to the climate and yet the response has been significant. That is scary; we have given the climate a huge kick when it responds to little tickles.

[sinimod]

I recently ran across this article by Clarke et al., 2006. They believe that the change was due to internal mechanisms as stated in the first sentence of the abstract to this long article:

The emergence of low-frequency, high-amplitude, quasi-periodic (~100-kyr) glacial variability during the middle Pleistocene in the absence of any change in orbital forcing indicates a fundamental change internal to the climate system.

and then they stated their belief in the length of the transition:

This middle Pleistocene transition (MPT) began 1250ka and was complete by 700ka.

I had not realized the transition from 41 ka glacial cycles to 100 ka cycles took over 500 ka to complete, although the authors did state that there is wide disagreement over how long the transition actually took:

there is wide disagreement in defining when the MPT occurred, with descriptions ranging from an abrupt versus gradual transition that began as early as 1500 ka and as late as 600 ka (e.g., Pisias and Moore, 1981; Prell, 1982; Ruddiman et al., 1989; Park and Maasch, 1993; Mudelsee and Schulz, 1997; Rutherford and D’Hondt, 2000).

[776281]

http://adsabs.harvard.edu/abs/2006AGUFMPP21B1688M
Drivers of the Middle Pleistocene Transition: the Role of the Southern Ocean in Modulating Changes in CO2 and the Transition to the 100ky World Martinez-Garcia, A.; Rosell-Mele, A.; McClymont, E. L.

The causes of Mid Pleistocene Transition (MPT) are still a matter of debate. Even its exact length is still being discussed. Thus the onset of the transition from 41 to 100kyrs in the pacing of the glacial-interglacial (G-IG) cycles is placed at different intervals between 1.5, 1.2 and 0.9 Ma. It has been argued that a decrease in CO2 could have led to the crossing of a climatic threshold that through different mechanisms would have changed the pacing of the G-IG (Berger et al., 1999; Paillard, 1998; Raymo, 1997). However, the causes of such a decrease in CO2, and its occurrence are uncertain. Here we show that the Southern Ocean could have played a key role in driving such a hypothetical decrease in atmospheric CO2.

http://www.nature.com/nature/journal...ture04123.html
Impacts of orbital forcing and atmospheric carbon dioxide on Miocene ice-sheet expansion
Ann Holbourn1, Wolfgang Kuhnt1, Michael Schulz2 & Helmut Erlenkeuser3

The processes causing the middle Miocene global cooling, which marked the Earth's final transition into an ‘icehouse’ climate about 13.9 million years ago (Myr ago)1, 2, 3, 4, remain enigmatic. Tectonically driven circulation changes5, 6 and variations in atmospheric carbon dioxide levels7, 8 have been suggested as driving mechanisms, but the lack of adequately preserved sedimentary successions has made rigorous testing of these hypotheses difficult. Here we present high-resolution climate proxy records, covering the period from 14.7 to 12.7 million years ago, from two complete sediment cores from the northwest and southeast subtropical Pacific Ocean. Using new chronologies through the correlation to the latest orbital model9, we find relatively constant, low summer insolation over Antarctica coincident with declining atmospheric carbon dioxide levels at the time of Antarctic ice-sheet expansion and global cooling, suggesting a causal link. We surmise that the thermal isolation of Antarctica played a role in providing sustained long-term climatic boundary conditions propitious for ice-sheet formation. Our data document that Antarctic glaciation was rapid, taking place within two obliquity cycles, and coincided with a striking transition from obliquity to eccentricity as the drivers of climatic change.

http://sp.lyellcollection.org/cgi/co...tract/247/1/19
Mid-Pleistocene revolution and the ‘eccentricity myth’
Mark A. Maslin1 & Andy J. Ridgwell2

The mid-Pleistocene revolution (MPR) is the term used to describe the transition between 41 ka and 100 ka glacial-interglacial cycles which occurred about one million years ago. Despite eccentricity having by far the weakest influence on insolation received at the Earth’s surface of any of the orbital parameters, it is often assumed to be the primary driver of the post-MPR 100 ka climate cycles. The traditional solution to this is to call for a highly nonlinear response by the global climate system to eccentricity. This ‘eccentricity myth’ is a simplified view of the relationship between global climate and orbital forcing and is in part due to an artefact of spectral analysis. Our aim here is to clarify the often confused role of eccentricity and review current theories of the MPR. We suggest that the post-MPR ‘100 ka’ glacial-interglacial cycles are more closely linked to precession, with the saw-toothed climate cycles being defined by every four or five precessional cycle. Because control over the number of precessional cycles involved is determined by eccentricity, eccentricity at most paces rather than drives the system. If true, then one must also question whether the MPR, itself defined by an abrupt change in spectral characteristics, is not also somewhat misconceived.

I am still very confused.
"eccentricity at most paces rather than drives the system"
"Here we show that the Southern Ocean could have played a key role "
"the relationship between global climate and orbital forcing and is in part due to an artefact of spectral analysis"

The orbital cycles may be the trigger but they do not explain the climatic response. So much is related but how?

[gazelle]

http://www.universetoday.com/70940/t...unspots-today/

Here's something we've not seen in a long while: five sunspots on the Sun at once. Is the Sun finally waking up from its unusually long and deep solar minimum slumber? While activity on the Sun usually ebbs and flows on a fairly predictable 11-year cycle, this current cycle has been anything but conventional. In 2009, there were 260 days (71% of the time) that the Sun was 'spotless,' but now in 2010 so far, the Sun has been spotless for only 35 days. With the last solar maximum occurring in 2001, maybe the Sun is just now ramping up to the next maximum, which is set for 2013. Recent solar flares on August 1 and 7, and now these sunspots may be signaling that the Sun is "throwing off the covers" and starting to wake up.

More images and commentary is available via http://www.solarcycle24.com/