|
|---|
|
Orbital Cycles &
Long-Term Climate Changes
Orbital
Climate Cycles:
2000 Yrs |
Long-Term Climate Changes: 2 Million | Tectonic Eras or Return to Short-Term Ocean-Based Climate Oscillations & Cycles links for: Earth Changes Bulletin: SUBSCRIBE | UNSUBSCRIBE ||| Update | Archive | Almanac
Gallery
~~~ |
|
Orbital Cycles & Long-Term Climate Changes
Abstract: [5-14-2007] This section continues the Earth Changes Storyboard about Earth's climate oscillations. The orbital cycles of the Earth-Moon System are outlined along with a summary of the long-term shifts the orbital cycles apparently produce in Earth's regional and/or global climate regimes. The primary objective of this portion of the Storyboard is to define the history of these cycles and how they combine to produce Earth's constantly changing climate regime. It is quite clear, in the historical profiles of mud and ice layers, that Earth's orbital cycles produce major swings in the prevailing climate regimes. These swings appear to far over- shadow the current and projected shifts of "Global Warming" during Century 21.
The layers of ice and mud which paleontologists study show also, quite clearly, that orbital climate shift is not the only game in town. Other natural phenomenon apparently also produce strong swings in climate of at least a few degrees Celcius. This can be seen very clearly in the wide variations of Solar Activity Cycle which have occurred during the past 1000 years in synchronicity with changes in the climates of the Northern Hemisphere. It can also be seen in many changes in average temperature in the ice sheets of Antarctica and Greenland in cycles which last from 200 to 2,000 years. These changes are far too short to be caused by the cycles of Earth's orbit, thus they must arise from a slightly unstable Sun and quite possibly from a slightly unstable Earth.
The graphs and charts of "chemistry" and deposits from the ancient past also provide considerable evidence to suspect that some of the observed climate changes in the past are produced by geophysical activity which causes periods of accelerated change. Apparently, as the fossilized records of the past make clear, the wobbling Earth itself, like the Sun, is less stable than humans would prefer to believe. There is much evidence which suggests that tectonic activity occasionally accelerates to produce rapid and radical changes in Earth's climate regimes, arising from eras of one or both of increased volcanism and/or of rapid changes in the orientation of the surface of the Earth to the equatorial plane of the solar system, ranging from small fractions of a degree up to tens of degrees.
As can be seen in the graphs of this Storyboard, the combined activity of cycles of change in the Sun, Earth's orbit, and geophysical shifts in the orientation of the Earth, can explain most of the signals in the fossil record. But alone, none of these three factors is sufficient to consistently explain the abundant evidence of frequent changes in regional and global climate regimes.
Orbital Cycles
& Long-Term Climate Changes
Note: The storyboard is under continuous development and expansion. A few links here are not working very well at the moment, and more may be added at any time.
Sunmary Of Major Findings Developed Uniquely Through This Study By MWM
Introduction To The Climate Storyboard
Table Of Contents For Climate Oscillations
Introduction To Long Term Climate Cycles
Background Information - Links to concepts, references, and major sources
Orbital Cycles
& Long-Term Climate Changes
El
|
|
Orbital Cycles
& Long-Term Climate Changes
Drawing upon a wide range of graphs, charts, and analytic findings about the chemicals trapped inside the layers of polar ice sheets and many other ancient sources, the climate records in the ice and mud deposits of earth clearly demonstrate that one of the primary drivers of long term changes in Earth's climate for any given latitude are variations in Earth's orbital cycles.
The depth of orbitally-induced recurring climate change during the past several hundred years clearly over-shadows the modest changes which have become known as "Global Warming". Humans are extremely worried about the implications of a 1 Celcius shift in climate, but the North Greenland Ice Sheet has revealed recurring and relatively rapid shifts in climate of up to 15 Celcius.
The primary range of the Earth's orbital cycles is from about 20,000 to 400,000 years.
Clearly point to the Sun as the long-term modifier of the overall climate regime. Currently, these are not producing any significant trend.
Many shorter term cycles, some of which clearly point to long-term Solar Activity Cycles.
The Global Warming issue, which has become as much an interesting study in social pandemics as it is an interesting body of information about the Earth, has stimulated a large and growing number of research studies in all the of Earth Sciences and in many astrophysical endeavors during the past 25 years. When looking at the current scientific literature, it seems like scarcely a rock, ocean-bottom, cosmic cycle, or layer of ice has not been looked under for clues to the whereabouts of the Global Warming Cause.
Immeasurably more is now known about the Earth as a result of all this new research. The rapidly growing sophistication in global reporting, database archiving, and scientific communication makes possible the finding of new findings at unprecedented rates. The result is an explosion of new ideas, relationships in data, and the emergence of new paradigms which are coalescing disparate information into some detailed understandings of the history and change of the Earth's climate and tectonic activity during the past couple of million years. Scientists can now describe, with reasonable proof, the annual snowfall in Northern Greenland a million years ago, the approximate swing in temperature for the year, and whether any major volcanic eruptions occurred in any given span of time during the the last hundred thousand years or so.
The explosion of scientific inquiry has clearly identified at least a dozen major cycles in the Earth's climate patterns. Many other minor cycles also have been identified and there does not yet seem to be a count of how many distinguishable cycles there may be.
Though it might have once seemed merely obvious, science can now demonstrate in very precise terms that the Sun, both metaphorically and literally, is the center of the climate change cycles on Earth and most probably on the other planets as well. Scientists can now detect a multiplicity of both climate cycles and solar cycles in tree rings, ice layers, sedimentary deposits on the ocean floor, and in other ways, which demonstrate that the many cycles of climate change are largely driven by cycles of Solar Activity and by cycles in Earth orbit around the Sun. Rhythmic changes in the size of tree rings, or isotopic chemical compositions in layers of mud and ice and other types of layers, can now be correlated with how the orbital cycles of many planets in our solar system combine through time to influence both the activity of the Sun and the shape and size of the orbit of the Earth.
Cyclical changes in Solar Activity, which appear to range from a few weeks to a few hundred years, and the changing shape and size of the orbit of the Earth, which occurs through tens of thousands of years, combine to profoundly affect Earth's climate. The largest shifts in the orbital cycles can now be traced backwards in time for the past two million years or so while the Solar Activity cycles can be traced backwards accurately for several thousand years, even to some extent for the past 400,000 years.
Many perplexing questions are being created by the growing knowledge of cycles of change in the Earth. If we compare climate data with past levels of Solar Activity for the past 400 years, it is very clear that cool and warm periods are most likely directly connected to changes in the general level of Solar Activity. In other words, the cooler the average temperature, the lower is the Sunspot Count, and vice verse, of course.
If we compare our present trends with the trend lines of the past, it would seem that Solar Activity is now trending downward and should continue to trend downward during Century 21 and that Global Cooling should be the inevitable result during the next 50 years. This of course contradicts the Global Warming that we can see is actually happening. Thus it is apparent that something else besides just Solar Activity is driving our current trend of Global Warming. This makes the profound question of the moment: what is this "something else".
The essence of these ocean climate cycles is ultra simple. Regions of the World Ocean alternate between periods of high or low pressure gradients which are produced by surface temperatures which are cooler or warmer than average. These cycles are seasonal of course, but there are also multi-year cycles of periods warmer or cooler than normal. One of the longest ocean climate cycles, the Northern Atlantic Cycle, appears to be some 20 years in length. But this may be surpassed by a Hurricane Cycle of xxx in length and a super El Nino Cycle of 50 years or more in length. , though the Hurricane cycle is a 20 year cycle
dblecheck hurricane cycle length get terminology descriptors consistent with this below Beyond the short term Ocean Oscillation Cycles (which we can think of as ranging predominately from 3 to 21 years in length) and the Solar Activity Cycles (which we can think of as ranging predominately between 8 to 400 years in length), we encounter the vastly longer orbital cycles. The Orbital Cycles range from the relatively short term seven year cycle in the size of Earth's wobble and the lunar eclipse cycle of 18.xxx years to the 100,000 and 400,000 cycles in the shape, size, and angle of the Earth's obit about the Sun's equator. add descriptors
Nearly all of the historical climate data reflect these cycles. Why? Primarily because of variations in the light received on Earth at any given latitude. The light varies directly with changes in Earth's orbital relationships with the Sun, the Moon, and the twisting, bobbing, wobbling changes in the orientation and location of the Spin Axis of the Earth.
These cycles are well defined and can be easily seen to be reflected in a variety of ways in the quantities of isotopes and chemical ions which are deposited in polar ice, ocean and lake sediments, tree rings, peat bogs. Scientists have learned how to use measurements of isotopes such as Oxygen-18 and Carbon-14 in various layers as "proxies" for defining changes in the warming and cooling trends of the climate. Carbon-14, for instance, can define the amount of light, the general trends in the Solar Activity Cycle, and the likely temperature changes through tens of thousands of years into the past. Oxygen-18 can track these trends backwards for millions of years. As these chemicals increase and decrease through vertical profiles of mud or ice, scientists can directly infer whether the amount of light hitting the surface of the Earth was increasing or decreasing during any given time.
As can be seen in the record of the rocks, ice, and sediments of Earth, variations in the sizes and connections between the orbital cycles produce significant climate change phenomenon on a regular cyclical basis. Cycles of 200, 40,000, 12,750, 25,500, 100000, and 400000 years have been defined during the past 10 years through a large number of studies, most especially the ice core studies on Antarctica conducted under Petrie. cite xxx please
These long range cycles range from xxx to 400,000 years in length. Three orbital cycle size, shape, and inclination of the Earth's orbit. Technically these are described by astrophysicists as the xxxx We can find the long range cycles, which range from about 12,500 years in length.
These are orbital cycles.
major cooling and warming eras.......
as much warming as... what is most interesting about these cycles is that CO2 appears to increase, AFTER the warming.
sudden shifts appear in the ice record in as little as 20 years. radical shifts,
These three are said to create what are called "the ice ages".
What makes the current climate change so extremely challenging to decipher is that there is no orbital factor which can produce any sudden shifts and nothing close to the amount of climate change we have seen in the past 100 years.
We are currently in the middle of a middling range of orbital cycles. No extremes, not much change during the last 1000 years and none to be expected during the next 1000 years. Thus, orbitally speaking, no trends here. Whatever is currently happening has no relationship to orbital factors and orbital graphs.
But, historically speaking, we have a profound mystery of substantial change which "looks like" some of the orbitally-induced climate shifts of the far past. Is it climate change induced by a very long Solar Activity Cycle, such one which is perhaps in the range of 1000 to 5000 years long? Or is it some unknown geophysical cycle? Or is this just a random fluctuation in the vast infinity of the cosmos?
Background Information & Knowledge/Data Sources:
Primary Data Series Used By MWM
|
|
Orbital
Cycles
Of The Moon The Lunar orbit is best described by what is known as the "Saros Cycle. (Saros is ancient Hellenic for "to repeat). It describes the a recurring sequence of eclipses which occurs through a span of about 18 years, after which the sequence nearly repeats. In essence the full cycle (almost) of all the main variations in the lunar orbit is 18 years. This is the length of time it takes to grind the lunar orbit through all its main variations caused by the EMS (Earth-Moon-Sun) system. Like the Earth's orbit, the lunar orbit is not round and regular. It changes its shape, speed, and its distance from the Earth. Variations also include the degree of inclinition or tilt of the Moon above and below the Earth's equator and the progression of the "nodes" where the tilted lunar orbit intersects the Earth's equator. "Saros" is the method of computing the "full deck" of lunar orbital variations. It was worked out several millennia ago and has not been improved upon, most likely by the Egyptians, who had the world's best observatories (the Temple of the Sun composed of Thoth's (Hermes) Three Great Benbens (Pyramids)) and the best calendrical system for recording time-related events. All this they passed down to the Summerians and Chaldeans, and through them to the Hellenes and Romans. For the Earth Sciences, one of the most important orbital cycles in the Saros scheme is what the ancients called the "Draconic month". The Draconic or Dragon Cycle is the time it takes (slightly more than 13.6 days) for the Moon to move from orbital node to node directly over the Equator . This is the time it takes for the Moon to swing above or below the equator by a few degrees (about 5) as it wings out on half of its orbit around the Earth and then return to a node (position directly on the equator) on its way to winging out on the opposite side of the equator. With respect to the Earth and all of its geophysical activities, this is the true orbital time period of the Moon. The full length of the Dragon Cycle is 27.21 days. During this cycle of 27 days , the distance of the Moon to the Earth varies fairly radically, by up to some 15%. This is why the Moon appears to change its size in the sky and occasionally look much larger than at other times. The closest approach is known as Perigee and the most distant point is called Apogee. This is a large nearly monthly variation in the shape and size of the Moon's orbit and it produces a large change in the Moon's gravity vectors acting on the Earth and the electromagnetic coupling of the Moon with Earth. To keep our minds nimble, the cosmic infintibulum makes the Perigee Cycle precess slightly from the Dragonic Cycle. The Perigee Cycle takes a few hours longer, some 27.5 days. This is probably due to the pull of the Sun attempting to retard the Moon's orbit every time it is rotating around behind the Earth away from the Sun. Or perhaps it is merely the drag of the electromagnetic bow "shock wave" which acts on the Moon every time it rotates out in between the Sun and the Earth. Here is how the numbers work on these cycles of the Moon:
Synodic Month (new moon to new moon)
29.53059 days = 29d 12h 44m For the Vortex paradigm of plate tectonics, the large variation in the Moon's gravity vector means that the Moon's pull on the Earth's continents pulses or waves in a slow moving cycle of about 27.5 days. This wave pumps the crust of the Earth, slowly pulls it apart in certain zones (The Great Rift, AKA the Mid Ocean Ridges, ) and slowly bunches it up on the eastern edges of the continents (where the greatest subduction zones are located). Since the Moon spends nearly half its time north of the Equator, and an equivalent time south of the Equator, the angle or vector of the pulling action varies constantly and is at an extreme angle relative to the Equator every 27.5 days. You have a South Moon or a North Moon for spells of 13.5 days each. This Dragon Month is different than the Synodic month, which is the length of time it takes for the Moon to return to a position of perfect alignment with the Sun and Earth, either as New at "0" degrees, or as Full at "180" degrees. The Synodic or Full Moon Cycle is what people experience as the primary Lunar orbit cycle while the Earth experiences the Draconic Month as the primary Lunar orbit cycle. The reason for the difference between the Synodic and the Dragon Months is that the Earth and Moon as a pair have completed nearly 1/13th of their combined orbit around the Sun in the time of one lunar orbit around the Earth. Since the moon is traveling more total distance than the Earth as it rotates around the Earth, it takes the Moon a little extra time to "catch up" with the Earth to achieve another perfect orbital alignment with the Sun. This time difference is nearly 2⅓ days This difference of course causes the "nodes" (where the Moon crosses the equator) to "precess" (or retard) to the west along the Equator. Each Full Moon and New Moon (solar alignments) are usually thus out of synchronization with the Dragon Nodes, only occasionally do they occur at nearly the same time during any given month. This would not matter at all if the Moon's orbit were on the same plane as the Equator. It is not, it is tilted by about 5%. This means that typically the Moon is South or North of the Equator most of the time, including during most Full and New Moons. It is only aligned on the Equator for roughly one day at a time, twice a month. It is this alignment which "precesses" by the 2.3 days each month. Consequently there cannot be eclipses twice a month, one of the Sun, the other of the Moon. Typically the Moon is a little above or below the Equator, avoiding the shadow of the Earth or off to one side of the Sun as seen from the Earth. The pattern of alignments repeats in an highly regular schedule, which makes the eclipses predictable far in advance. Known as the Saros precession, an eclipse or any given alignment sequence takes 18 years to return the nodes to the same position relative to both the Earth and the Sun. If there's an eclipse
now, in 6585.322 days from now, from Espenak http://sunearth.gsfc.nasa.gov/eclipse/SEsaros/SEsaros.html
Any two eclipses separated by one saros cycle share very similar
geometries. They occur at the same node with the Moon at nearly the
same distance from Earth and at the same time of year. Because the
saros period is not equal to a whole number of days, its biggest
drawback is that subsequent eclipses are visible from different
parts of the globe. The extra 1/3 day displacement means that Earth
must rotate an additional ~8 hours or ~120º with each cycle. For
solar eclipses, this results in the shifting of each successive
eclipse path by ~120º westward. Thus, a saros series returns to
about the same geographic region every 3 saroses (54 years and 34
days). Since there are two to five solar eclipses every year, there are approximately forty different saros series in progress at any one time. For instance, during the later half of the twentieth century, there are 41 individual series and 26 of them are producing central eclipses. As old series terminate, new ones are beginning and take their places. To illustrate, the ten central solar eclipses of 1891, 1909, 1927, 1945, 1963, 1981, 1999, 2017, 2035 and 2053 are all members of Saros 145. The series began with a partial eclipse near the north pole in 1639. The first central eclipse of the series was an annular eclipse in 1891. It was followed by another annular in 1909. The next event was the first total eclipse in 1927. The total solar eclipse of 1999 August 11 is number 21 of 77 eclipses in Saros 145, and it is the 5th of 41 total eclipses in the series. Each of the subsequent total eclipses shifts southwards. The last total eclipse occurs in 2648 near the south pole. The last eclipse of the series takes place in 3009. Table of Saros 145 gives details for every eclipse in the series.
But there is an important qualifier to this cycle. Almost. Nothing orbitally comes in whole simple numbers in simple isolated self-referential systems, thus all orbits everywhere reflect synchronicity of the cosmic infintibulum in the unitary field state. The net effect is that the return of the alignment after 18 years also precesses slightly against both the Dragon and Perigee 18 year cycles. This adds up to a Grand Saros cycle of about 1200 years during which the sequence gradually disappears and is replaced by other eclipse sequences. At any given time, the astrophysicists tell us, there are about 70 Saros Sequences in play, allowing any specific type of eclipse to be predicted every 18 years for a 1000 years. When the Moon is as high in latitude north of the Equator as it can get - about 5 degrees - it it said to be in its North Node. And so forth for the South Node. The alignments of these high nodes with the position of the Sun is of profound importance. Every 18.5 years this alignment will achieve the most extreme separation of the Moon and the Earth, a separation of about 27 degrees. This will occur during the Solstices when the Sun is as far to the South or North as it gets during any given year. When the Moon is in Perigee while the Node of the Moon's orbit is as fully separated from the position of the Sun in the opposite hemisphere on the other side of the Equator, the Earth is maximally stressed by a combination of rapidly changing gravitational and spin vectors. Truly Great Quakes tend to occur on these Saros extremes. The Great Tectonic Rupture off Sumatra, one of the greatest tectonic events ever recorded by humans during Christmas 2004 occurred during a near 18.5 year extreme on the Saros Cycle during a Full Moon Perigee. Think of this as a Four-Factor Cosmic Whammy (Full Opposition - Perigee - Perihelion - Nodal Differential), each component of which affects the gravity vectors operating on the spinning mass of the Earth. This synchronicity cannot be a coincidence. Clearly the alignment of orbital vectors induced sufficient stress to crack and move - significantly - by tens of meters vertically and hundreds of meters laterally - major sections of two large tectonic plates. When a solar eclipse occurs at a New Moon (when of course the Moon is nearly directly over the Equator), then at the next Full Moon it is likely that the the Moon has already passed over into its opposite node. It may or may not be hidden briefly by Earth's shadow in a full or partial eclipse. The next New Moon will be even further behind the transition to the opposite node, thus it is unlikely that there will be a solar eclipse. And so forth, until the two converge again. About 5 or 6 lunar cycles later the New Moon will fall close to a nodal transition over the Equator, thus another round of eclipses (one or at maximum two) can occur. Thus eclipses in the Saros Cycle occur in a 1 or 2 month period twice a year. All this has obvious implications for geophysical plate tectonics but what connection is there to climate? That is a very interesting question which is not easy to answer at this time with proof. It is possible, however, to clearly demonstrate that there is an 18.5 year cycle in the weather patterns. Clearly a lunar influence affects the Earth's atmosphere. Though it cannot be yet clearly demonstrated in this Storyboard, the most likely candidate is the same force which produces the ocean climate regimes: underwater volcanism. The extremes of the nodal relationships with the position of the Sun may produce a cycle of increasing and decreasing heat into the bottoms of the oceans, which is distinctly different than the 3.5 year El Nino Cycle.
and most likely the ocean climate regimes. Most likely through the lunar For additional information on the Saros Cycle: Access To Info On Eclipses: http://sunearth.gsfc.nasa.gov/eclipse/eclipse.html Five Thousand Years of Lunar Eclipses - A NASA Catalog - here is the master catalog to the Lunar events which so worried the ancients that they invented the science of astronomy to keep track of them http://sunearth.gsfc.nasa.gov/eclipse/LEcat/LEcatalog.html Fred Espenak at NASA: "Eclipses and the Saros"; http://sunearth.gsfc.nasa.gov/eclipse/SEsaros/SEsaros.htmlMore exact numbers provided by Espenak. These are averages - keep in mind that there are variations in all of the orbits) Synodic Month: 29.530589 days Dragon Month: 27.21222 days Perigee or the
"Anomalistic Month": 27.55455 days. The precession of the Moon's Nodes (backwards) of 19-20 degrees a year makes the Dragon year shorter than the usual calendar year. It's average length is 346.62005 days. Any particular eclipse cycle: 47 synodic months (1387.938 days) corresponding with 51 draconic months (1387.822 days), featuring an eclipse every 3.8 years. These cycles all repeat
nearly exactly every 18+ years because: 223 synodic months (6585.321 days) almost equal 242 draconic months (6585.357 days), a period of 18 years 10 and 1/3 (or 11 and 1/3) days -- depending on the number of intervening leap years. The second Saros (446
full Moons) afterwards, the eclipse comes some 16 hours later and
240 degrees westward. The third Saros (669 full Moons) finds the
eclipse coming full circle, happening at about the same time and
place. This Triple Saros is called an Exeligmos, a period
representing some 54 years and 34 days. A typical Saros series consists of 69 to 86 eclipses spanning well over a thousand years. Eventually the eclipses produce no shadow and the sequence is considered dead. There are around 40 different Saros series in operation at any one given time.
But, unlike the Sun, the maximum and minimum declination reached by the Moon also varies. This is because the orbit of the Moon's revolution about the Earth is inclined by about 5° to the orbit of the Earth's revolution around the Sun, and so the maximum declination of the Moon varies from (23.5°-5°)=18.5° to (23.5°+5°)=28.5°. The effect of this is that at one particular time (the minor lunar standstill), the Moon will change its declination during the month from +18.5° to -18.5°, which is a total movement of 37°. This is not a particularly big change, and may not be very noticeable in the sky. However, 9.3 years later, during the major lunar standstill, the Moon will change its declination during the month from +28.5° to -28.5°, which is a total movement of 57°, and which is enough to take it from high in the sky to low on the horizon in just two weeks.
Inclination: 5.145° to
ecliptic Angular size: from 29′to 33′ Perigee: 363,104 km (0.0024 AU) Apogee: 405,696 km (0.0027 AU) Axial tilt: 1.5424° (to ecliptic) Obliquity: 6.687° (to orbit plane) |
|
Long Term Climate Cycles
|
|
2000 Year Climate Cycles Climate
|
|
The 200 Year
"deVries" Solar Activity Cycle
Solar or
Geophysical? "It is commonly believed that the ~200- year deVries cycle is one of the most intense solar cycles (Vasil’ev et al., 1999, Wagner et al., 2001). This is evidenced, for instance, by the occurrence of pronounced solar activity minima (Maunder, Spörer, Wolf ) in approx. 200-year intervals during the last millennium. The temporal coincidence between the Maunder (AD 1645-1715), Spörer (AD 1416-1534), and Wolf periods (AD 1280-1350) and the expansion of Alpine glaciers indicates a climatic response to these solar minima (Eddy, 1976). A similar conclusion was recently inferred from an analysis of glacier expansion in Alaska (Wiles et al., 2004)." (Raspopov et al, 2006) Here, we aim to reveal the deVries
O. Raspopov :
SPbF IZMIRAN, St. Petersburg, Russia;
oleg@OR6074.spb.edu
|
|
Chart
of Temperature Proxy Variations For Holocene Era This
|
|
Orbital Cycles Eccentricity: shape of the Earth's Orbit
If the Earth's orbit were a perfect circle, the amount of insolation or sunlight hitting the Earth would vary only with the Solar Activity Cycles. But the Earth's orbit is not a perfect circle, it is slightly distorted into an egg- shape, which the astrophysicists define as an ellipse. The amount of this distortion is called the eccentricity of the Earth's orbit and it is measured as a unit of ellipsicity, which indicates the amount of variation from a perfect circle. The eccentricity of the Earth's orbit varies between nearly 0 (a perfect circle to almost 0.05, currently it is 0.0167 and it is getting smaller.
Astrophysicists believe that gravitational attractions between the planets produce some eccentricity in all the orbits of the planets, and the amount of course varies widely.
Through time, the eccentricity of the Earth's orbit slowly changes f(see graph [1]). This graph shows the variation in the eccentricity of the Earth's orbit over the last 750,000 years. The blue line traces the eccentricity of the elliptical orbit as it varies from from circular (0.0).. The orange line shows today's value for comparison. The data are from Berger and Loutre (1991). In other values, Mercury (with an eccentricity of 0.2056) holds the title as the largest value among the planets of the Solar System. Orbital mechanics require that the duration of the seasons be proportional to the area of the Earth's orbit swept between the solstices and equinoxes, so when the orbital eccentricity is extreme, the seasons that occur on the far side of the orbit (aphelion) can be substantially longer in duration. Today, northern hemisphere fall and winter occur at closest approach (perihelion), when the earth is moving at its maximum velocity. As a result, fall and winter are slightly shorter than spring and summer. In 2006, summer is 4.66 days longer than winter and spring is 2.9 days longer than fall [2]. Axial precession slowly changes the place in the Earth's orbit where the solstices and equinoxes occur. Over the next 10,000 years, northern hemisphere winters will become gradually longer and summers will become shorter. Any cooling effect, however, will be counteracted by the fact that the eccentricity of Earth's orbit will be almost halved, reducing the mean orbital radius and raising temperatures in both hemispheres closer to the mid-interglacial peak.
Milankovitch_Variations.png
Inclination: t This figure shows the variations in Earth's orbit, the resulting changes in solar energy flux at high latitude, and the observed glacial cycles. According to Milankovitch Theory, the precession of the equinoxes, variations in the tilt of the Earth's axis (obliquity) and changes in the eccentricity of the Earth's orbit are responsible for causing the observed 100 kyr cycle in ice ages by varying the amount of sunlight received by the Earth at different times and locations, particularly high northern latitude summer. These changes in the Earth's orbit are the predictable consequence of interactions between the Earth, its moon, and the other planets. The orbital data shown is from Quinn et al. (1991). Principal frequencies for each of the three kinds of variations are labeled. The solar forcing curve (aka "insolation") is derived from July 1st sunlight at 65 °N latitude according to Jonathan Levine's insolation calculator [1]. The glacial data is from Lisiecki and Raymo (2005) and gray bars indicate interglacial periods, defined here as deviations in the 5 kyr average of at least 0.8 standard deviations above the mean. This figure shows the variations in Earth's orbit, the resulting changes in solar energy flux at high latitude, and the observed glacial cycles. This image is intended to replace Image:Milankovitch_patterns.jpg. http://en.wikipedia.org/wiki/Image:Milankovitch_patterns.jpg
Milankovitch_patterns.jpg (406 × 247 pixel, file size: 92
KB, MIME type: image/jpeg)
Calculated Milankovitch variations and actual glacial and thermal pattern. USGS; posted at Wikipedia Image from Global Warming Art
Obliquity & Precession.
In astronomy, Axial tilt is the inclination angle of a planet's rotational axis in relation to a perpendicular to its orbital plane. It is also called axial inclination or obliquity. The axial tilt is expressed as the angle made by the planet's axis and a line drawn through the planet's center perpendicular to the orbital plane.
|
||||||||||||||||||||||||||||||||||||
| Season (Northern Hemisphere) Durations | |||
| data from United States Naval Obervatory | |||
| Year | Date: GMT | Season Duration | |
|---|---|---|---|
| 2005 | Winter Solstice | 12/21/2005 18:35 | 88.99 days |
| 2006 | Spring Equinox | 3/20/2006 18:26 | 92.75 days |
| 2006 | Summer Solstice | 6/21/2006 12:26 | 93.65 days |
| 2006 | Fall Equinox | 9/23/2006 4:03 | 89.85 days |
| 2006 | Winter Solstice | 12/22/2006 0:22 | 88.99 days |
| 2007 | Spring Equinox | 3/21/2007 0:07 | |
Orbital mechanics require that the length of the seasons be proportional to the areas of the seasonal quadrants, so when the eccentricity is extreme, the seasons on the far side of the orbit can be substantially longer in duration. When autumn and winter occur at closest approach, as is the case currently in the northern hemisphere, the earth is moving at its maximum velocity and therefore autumn and winter are slightly shorter than spring and summer. Thus, summer in the northern hemisphere is 4.66 days longer than winter and spring is 2.9 days longer than fall. Source
The Earth's rotation axis wobbles, causing a slow 2.4° change in the tilt of the axis (obliquity) with respect to the plane of the Earth's orbit. The obliquity variations are roughly periodic, with a period of approximately 41,000 years. When the obliquity increases, the amplitude of the seasonal cycle in insolation increases, with summers in both hemispheres receiving more radiative flux from the Sun, and the winters less radiative flux. As a result, it is assumed that the winters become colder and summers warmer.
But these changes of opposite sign in the summer and winter are not of the same magnitude. The annual mean insolation increases in high latitudes with increasing obliquity, while lower latitudes experience a reduction in insolation. Cooler summers are suspected of encouraging the start of an ice age by melting less of the previous winter's ice and snow. So it can be argued that lower obliquity favors ice ages both because of the mean insolation reduction in high latitudes as well as the additional reduction in summer insolation.
Presently the Earth is tilted at 23.44 degrees from its orbital plane, roughly half way between its extreme values.
Movies
A movie depicting Earth's changing orbit over the
last 100Ky. The orientation is such that spring equinox (indicated
by a vertical bar) is directly to the front with the sun behind it.
Northern Hemisphere summer is to our right, and Northern Hemisphere
winter is to the left. The apsidal (dashed) line connects perihelion
(Earth's closest approach to the sun) to aphelion (the point when
Earth is furthest from the sun). The rotaion of the apsidal line
occurs because of the precession of the equinoxes and has a roughly
twenty-two thousand year period. The semi-circle around the Earth
indicates the location of the equator and the straight line is the
polar axis. Obliquity is defined as the angle beetween the orbital
and equatorial planes. The variations in Earth's obliquity and the
eccentricity of Earth's orbit have both been increased in magnitude
by a factor of ten. Also, the Earth's angular velocity has been
decreased by a factor of five thousand. Note that Earth's angular
velocity is slowest at aphelion and fastest at perihelion.
Earth's variable orbit (74 MB, avi format)
http://en.wikipedia.org/wiki/Milankovitch_cycle
180px-Earth_obliquity_range.jpg
180px-Earth_precession.jpg
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.
More recent researchers noted this drift and that the orbit also moves relative to the orbits of the other planets. The invariable plane, the plane that represents the angular momentum of the solar system, is approximately the orbital plane of Jupiter. The inclination of the Earth's orbit has a 100,000 year cycle relative to the invariable plane. This 100,000 year cycle closely matches the 100,000 year pattern of ice ages.
It has been proposed that a disk of dust and other debris is 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.[1][2]
Because the observed periodicities of climate fit so well with the orbital periods, the orbital theory has overwhelming support. Nonetheless, there are several difficulties in reconciling theory with observations.
The 100,000 year problem is that the eccentricity variations have a significantly smaller impact on solar forcing than precession or obliquity and hence might be expected to produce the weakest effects. However, observations show that during the last 1 million years, the strongest climate signal is the 100,000 year cycle. In addition, despite the relatively large 100,000 year cycle, some have argued that the length of the climate record is insufficient to establish a statistically significant relationship between climate and eccentricity variations.[3] Some models can however reproduce the 100,000 year cycles as a result of non-linear interactions between small changes in the Earth's orbit and internal oscillations of the climate system.[4][5]
The 100,000 year problem is that the eccentricity variations have a significantly smaller impact on solar forcing than precession or obliquity and hence might be expected to produce the weakest effects. However, observations show that during the last 1 million years, the strongest climate signal is the 100,000 year cycle. In addition, despite the relatively large 100,000 year cycle, some have argued that the length of the climate record is insufficient to establish a statistically significant relationship between climate and eccentricity variations.[3] Some models can however reproduce the 100,000 year cycles as a result of non-linear interactions between small changes in the Earth's orbit and internal oscillations of the climate system.[4][5]
The 400,000 year problem is that the eccentricity variations have a strong 400,000 year cycle. That cycle is only clearly present in climate records older than the last million years. If the 100ky variations are having such a strong effect, the 400ky variations might also be expected to be apparent. This is also known as the stage 11 problem, after the interglacial in marine isotopic stage 11 which would be unexpected if the 400,000 year cycle has an impact on climate. The relative absence of this periodicity in the marine isotopic record may be due, at least in part, to the response times of the climate system components involved - in particular, the carbon cycle.
The stage 5 problem refers to the timing of the penultimate interglacial (in marine isotopic stage 5) which appears to have begun 10 thousand years in advance of the solar forcing hypothesized to have been causing it. This is also referred to as the causality problem.
Various internal characteristics of climate systems are believed to be sensitive to the insolation changes, causing amplification (positive feedback) and damping responses (negative feedback).
The unsplit peak problem refers to the fact that eccentricity has cleanly resolved variations at both 95 and 125 ky frequencies. A sufficiently long, well-dated record of climate change should be able to resolve both frequencies, but some researchers interpret climate records of the last million years as showing only a single spectral peak at 100 kyr periodicity. It is debatable whether the quality of existing data ought to be sufficient to resolve both frequencies over the last million years.
The transition problem refers to the change in the frequency of climate variations 1 million years ago. From 1-3 million years, climate had a dominant mode matching the 41 ky cycle in obliquity. After 1 million years ago, this changed to a 100 ky variation matching eccentricity. No reason for this change has been established.
An often-cited 1980 study by Imbrie and Imbrie determined that "Ignoring anthropogenic and other possible sources of variation acting at frequencies higher than one cycle per 19,000 years, this model predicts that the long-term cooling trend which began some 6,000 years ago will continue for the next 23,000 years."[7]
More recent work by Berger and Loutre suggests that the current warm climate may last another 50,000 years.[8]
Nearly as soon as the ice ages were discovered, their origin was attributed to astronomical causes. In the late 1800s, James Croll assumed that the ice ages were driven by changes in insolation (solar heating) brought about by variations in the Earth's orbit and spin axis (1, 2). According to Croll, and to Milankovitch after him (3, 4), the main orbital parameters that affect insolation and its distribution are the Earth's orbital eccentricity, obliquity (tilt of the Earth's poles towards the sun), and precession (lag between equinox and perihelion). However, it was not until 1970 that Broecker and van Donk (5) established that glaciation in the late Pleistocene was truly periodic, and dominated by a 100 k.y. cycle. This period was soon identified with the quasi-periodic 100 k.y. cycle of the Earth's eccentricity. (We will offer evidence that this identification was premature.) In addition another strong cycle was discovered with a 41 k.y. period that matched the cycle of changes in the Earth's obliquity (8). This 41 k.y. cycle appears to have dominated glacial changes from 1.5 to 2.5 Ma (6). The 100 k.y. cycle has dominated from the present back to 1 Ma.
ABSTRACT: Narrow spectral features in ocean sediment records offer strong evidence that the cycles of glaciation were driven by astronomical forces. Two million years ago the cycles match the 41 k.y. period of the Earth's obliquity. This supports the Croll/Milankovitch theory, which attributes the cycles to variations in insolation. But for the last million years, the spectrum is dominated by a single 100 k.y. feature, and is a poor match to the predictions of insolation models. The spectrum can be accounted for by a theory which derives the cycles of glaciation from variations in the inclination of the Earth's orbital plane.
100,000 Year Climate Cycles
The story of Global Warming
not sure how to connect this
http://en.wikipedia.org/wiki/Image:Five_Myr_Climate_Change.png
The observed isotope variations are very similar in shape to the temperature variations recorded at Vostok, Antarctica during the 420 kyr for which that record exists. Hence the right hand scale of the figure was established by fitting the reported temperature variations at Vostok (Petit et al. 1999) to the observed isotope variations. Hence, this temperature scale should be regarded as approximate and its magnitude is only representative of Vostok changes. In particular, temperature changes at polar sites, such as Vostok, frequently exceed the changes observed in the tropics or in the global average. A horizontal line at 0 °C indicates modern temperatures (circa 1950).
Labels are added to indicate regions where 100 kyr and 41 kyr cyclicity is observed. These periodicities match periodic changes in Earth's orbital eccentricity and obliquity respectively, and have been previously established by other studies (not relying on orbital tuning). For discussion of how such orbital changes might drive climate change, see Milankovitch cycles.
this is the real volstok chart
http://upload.wikimedia.org/wikipedia/en/7/77/Vostok_420ky_4curves_insolation.jpg
|
Chart Of
Climate Change For Last 90,000 Years As Extrapolated From The Ice Cores of Greenland and Antarctica line graph in portrait orientation by "Pages" Show as is and add second version with the Phoenix Event Horizons added as vertical lines. This chart published in 2006 is the most "finished" calibration of the paleo-climatology research which culminated with the findings of the ice core studies by Petit et al in in Antarctica and then sparked a major round of expansion in other "ice core" study projects. This particular chart shows the calibration which has been made by scientists to tie the evidence together at both ends of the Earth. How did they do it. They used primarily the Earth's orbital "eccentricity" cycle of 100,000 years. They also used the two other major orbital cycles (obliquity of the axis orientation to the polar stars and the precession of the axis orientation at Perihelion). Collectively these are known as the Milankovitch Cycles. By far, the most important is the cycle of expansion and contraction in the elliptical shape of the Earth's orbit around the Sun. This is called the eccentricity of the Earth and it varies by xxx to xxxx. This is more than enough to produce a very strong foot print in the climate of the Earth such that the 100.000 year swing can be clearly seen in nearly all Earthly phenomon which can be studied through such a long period of time. Please note that this chart is highly crafted to steer your perceptions. Missing for instnace is the last 10,000 years, which would show as a high plateau on the graph. How would that compare with the previous hills and valleys? Well...that becomes a very long story which boils down to a lot of hemming and hawing. Such questions could steer one away from focusing on the current topic of Global Warming, The institutionalized paleo researchers are not ready to deal with such issues and potential distractions at the current time.
The fact that these changes are happening at both ends of the Earth simultaneously, mostly, ties ALL climate change directly to the Solar Cycles ranging from the Solar Activity Cycle of 11 years through several historical length cycles up to about 3500 years in length (which are most likely related to Lunar and planetary influlcnces on the Earth's orbit) and then through the longer term Polar and Obital Cycles (Milankovitch, so-called). From the point of view of the Phoenix phenomenon, the Northern Greenland Ice studies are almost certainly the best best data. These ice sheets were the most impacted by the shiftings of the Spin Axis during the past 125,000 years, From other sources of data, we know that there were at least four primary shifts in the general location of the Spin Axis (mistaken widely by paleo people as "ice ages") and many smaller shifts. These can now be very well defined on this chart.
Blunier & Brook, 2001 Science 5 January 2001: Reports "Timing of Millennial-Scale Climate Change in Antarctica and Greenland During the Last Glacial Period" Thomas Blunier,1* Edward J. Brook2 A precise relative chronology for Greenland and West Antarctic paleotemperature is extended to 90,000 years ago, based on correlation of atmospheric methane records from the Greenland Ice Sheet Project 2 and Byrd ice cores. Over this period, the onset of seven major millennial-scale warmings in Antarctica preceded the onset of Greenland warmings by 1500 to 3000 years. In general, Antarctic temperatures increased gradually while Greenland temperatures were decreasing or constant, and the termination of Antarctic warming was apparently coincident with the onset of rapid warming in Greenland. This pattern provides further evidence for the operation of a "bipolar see-saw" in air temperatures and an oceanic teleconnection between the hemispheres on millennial time scales.
1 Department of Geosciences, Guyot Hall, Princeton University, Princeton,
NJ 08544, USA; Climate and Environmental Physics, Physics Institute,
University of Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland.
THIS IS THE BEST ONE http://en.wikipedia.org/wiki/Image:Epica-vostok-grip-ngrip-o18.png
Note that the GRIP and NGRIP Dansgaard-Oeschger events should be co-incident; but the timescales are not absolutely referenced. so they appear not to be. Note also that the NGRIP data is regular in time but the GRIP data in depth, hence the apparent greater variability of GRIP in the current interglacial is not real. The greater warmth of NGRIP than GRIP in the current interglacial, but roughly equal warmth in the glacial, is probably real. After 110 kyr the GRIP and NGRIP cores clearly differ: the NGRIP core is reliable, the GRIP core is unreliable due to ice folding near the base.
GRIP data from http://www.nsidc.org/data/gisp_grip/data/grip/isotopes/gripd18o.dat.
By William M. Connolley.
http://en.wikipedia.org/wiki/Image:Ice-core-isotope.png
Dansgaard-Oeschger events are rapid climate fluctuations during and at the end of the last ice age. Twenty-three such events have been identified between 110,000 and 23,000 years BP.
In the Northern Hemisphere, they take the form of rapid warming episodes, typically in a matter of decades, each followed by gradual cooling over a longer period. For example, about 11,500 years BP, averaged annual temperatures on the Greenland icepack warmed by around 8°C over 40 years, in three steps of five years (see Alley (2000), Stewart chap 13) - 5°C change over 30-40yrs more common.
The processes behind the timing and amplitude of these events (as recorded in ice cores) are still unclear. The pattern in the Southern Hemisphere is different, with slow warming and much smaller temperature fluctuations. Indeed, the Vostok ice core was done before the Greenland cores, and the existence of Dansgaard-Oeschger events was not widely recognised until the Greenland (GRIP/GISP2) cores were done; after which there was some reexamination of the Vostok core to see if these events had somehow been "missed".
Image in higher resolution (981 × 567 pixel, file size: 11 KB, MIME type: image/png) http://en.wikipedia.org/wiki/Image:Ngrip-epica-do18.png delta-O-18 from the NGRIP (black) and EPICA (blue) ice cores.
delta-O-18 is a temperature proxy. Higher values are warmer. The left hand side shows the current interglacial. The right hand side is the previous Eemian interglacial which is incomplete in the NGRIP data. During the glacial period the NGRIP core shows clear signs of Dansgaard-Oeschger events which are muted in the EPICA core.
By William M. Connolley.
NGRIP is an abbreviation for the North Greenland Ice Core Project.
The NGRIP drilling site is near the center of Greenland (75.1 N, 42.32 W, 2917 m, ice thickness 3085). Drilling began in 1999 and was completed at bedrock in 2003 [1]. The cores are cylinders of ice four inches in diameter that were brought to the surface in 3.5-meter lengths. The NGRIP site was chosen to extract a long and undisturbed record stretching into the last glacial, and it succeeded. The site was chosen for a flat basal topography to avoid the flow distortions that render the bottom of the GRIP and GISP cores unreliable. Unusually, there is melting at the bottom of the NGRIP core - believed to be due to a high geothermal heat flux locally. This has the advantage that the bottom layers are less compressed by thinning than they would otherwise be: NGRIP annual layers at 105 kyr age are 1.1 cm thick, twice the GRIP thicknesses at equal age.
The NGRIP record helps to resolve a problem with the GRIP record - the unreliability of the Eemian interglacial portion of the record. NGRIP covers 5 kyr of the Eemian, and shows that temperatures then were roughly as stable as the pre-industrial Holocene temperatures were. This is confirmed by sediment cores, in particular MD95-2042 [2].
In 2003, NGRIP recovered what seem to be plant remnants nearly two miles below the surface, and they may be several million years old. [3] "Several of the pieces look very much like blades of grass or pine needles," said University of Colorado at Boulder geological sciences Professor James White, an NGRIP principal investigator. "If confirmed, this will be the first organic material ever recovered from a deep ice-core drilling project," h
|
|
Cha 140,000
This
This |
|
Chart Of 140,000
This simple chart is one of the most important
This |
|
400,000 Year Climate Cycles The story of Global Warming is best begun with thming" Climate
400,000 Year Earth History Chart For CO2 & Temperature By U.N. GRID
UNEP Trend Data produced by GRID-Arendal, see http://www.grida.no/climate/vital/
Petit, J.R.& Jouzel, J. et al (international team of 18): “Climate And Atmospheric History Of The Past 420,000 Years From The Vostock Ice Core In Antarctica"; Nature 399, 429 - 436 (June 3 1999); doi:10.1038/20859 For summary chart produced from the ice-core data by Petit et al for the UNEP, go to http://www.grida.no/climate/vital/02.htm or download from http:/www.michaelmandeville.com/earthmonitor/atmosphere/400000_yr_co2temp.jpg
Petit, J.R et al (international team): “Historical isotopic temperature record from the Vostok ice core”, in Trends: “A Compendium of Data on Global Change; Carbon Dioxide Information Analysis Center”, produced by Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge TN, USA. http://cdiac.esd.ornl.gov/trends/temp/vostok/jouz_tem.htm. To access the data files for the charts, go to http://www.ncdc.noaa.gov/paleo/icecore/antarctica/vostok/vostok_isotope.html Correspondence and requests for materials should be addressed to J.R.P. (e-mail: petit@glaciog.ujf-grenoble.fr.) United Nations Environmental Program (UNEP) and the United Nations WMO: “Introduction To Climate Change”, produced by GRID-Arendal, 2001-2006, on the Iway at http://www.grida.no/climate/vital/ See especially http://www.grida.no/climate/vital/02.htm for the graphs from the Vostok Ice Cores which have become the stock in trade for displaying and talking about global warming and climate change. Questions about GRID-Arendal or environmental information: grid@grida.no
UNEP Programs, see http://www.grida.no/activities.cfm?pageID=2
UNEP Trend Data produced by GRID-Arendal, see http://www.grida.no/climate/vital/
UNEP anon analysts: “Observed Climate Change”; 2001-2006, GRID-Arendal, see http://72.14.203.104/u/grida?q=cache:FIiCTKV9-_8J:www.grida.no/climate/vital/17.htm+0.3+to+0.6%3FC+since+the+late+19th+century&hl=en&gl=us&ct=clnk&cd=2&ie=UTF-8
UN ICPP - Intergovernmental Panal On Climate Change: http://www.ipcc.ch/; by default, the greenhouse gas lobby
U.N. Intergovernmental Panal On Climate Change (UNEP under WMO), in a web document titled "Climate Change 2001", at http://www.grida.no/climate/ipcc_tar/wg1/105.htm#fig32 or http://www.grida.no/climate/ipcc_tar/wg1/fig3-2.htm These are the charts used by world weather experts which were built from the Keeling datafiles at Scripps in San Diego. UNEP: “Potential Impacts of Climate Change”, as of 2006, on the Iway at http://www.grida.no/climate/vital/impacts.htm].
United Nations International Strategy for Disaster Reduction (UN/ISDR) & the Louvain Research Center in Belgium (CRED): “Disasters Increase By 18 Per Cent In 2005, But Death Rates Drop”; press release of January 30, 2006. http://www.unisdr.org/eng/media-room/press-release/2006/PR-2006-02-Disasters-increase-18-per-cent-2005-but-death-rates-drop.pdf]
|
|
Chart Of 1890-2006
This
|
|
Chart 400,000 Vostok_420ky_4curves_insolation.jpg This
|
|
Exp90-2006 distorts the horizontal...these are Earth's Orbital Cycles much is made in the literature about a "switch" from 100 kyr EO cycle to 41 kyr EO cycle as "climate cycles" both components are still in the chart no matter what the time frame, but the obliquity signal is not as apparant during the past 400 kyr. what is the difference? a shift in the general location or oscillation pattern of the Spin Axis which easily account for this result in the climate records. That, or a direct change in the orbit spin of the Earth. making for instance, the obliquity smaller. that what do it. So from the point of view of paleo climate, ONE of the major and rather important mysteries, is what is the Event in the Horizon of 500 to 900 kyrs? orbital or axial? if axial, what axial?
line graph in portrait
orientation
|
|
Oxygen-18
Profile For Five Million Years Of Climate
This
This |
|
Chart Of 1890-2006
This
http://en.wikipedia.org/wiki/Image:Phanerozoic_Carbon_Dioxide.png This figure shows estimates of the changes in carbon dioxide concentrations during the Phanerozoic. Three estimates are based on geochemical modeling: GEOCARB III (Berner and Kothavala 2001), COPSE (Bergmann et al. 2004) and Rothman (2001). These are compared to the carbon dioxide measurement database of Royer et al. (2004) and a 30 Myr filtered average of those data. Error envelopes are shown when they were available. The right hand scale shows the ratio of these measurements to the estimated average for the last several million years (the Quaternary). Customary labels for the periods of geologic time appear at the bottom.
Direct determination of past carbon dioxide levels relies primarily on the interpretation of carbon isotopic ratios in fossilized soils (paleosols) or the shells of phytoplankton and through interpretation of stomatal density in fossil plants. Each of these is subject to substantial systematic uncertainty.
Estimates of carbon dioxide changes through geochemical modeling instead rely on quantifying the geological sources and sinks for carbon dioxide over long time scales particularly: volcanic inputs, erosion and carbonate deposition. As such, these models are largely independent of direct measurements of carbon dioxide.
Both measurements and models show considerable uncertainty and variation; however, all point to carbon dioxide levels in the past that have been signifcantly higher than they are at present.
[edit] Copyright
This figure was prepared by Robert A. Rohde from published data and is incorporated into the Global Warming Art project. Note that d-O-18 is a proxy for temperature: more negative is colder; the period from 20 to 10 kyr shows the rise in temperature at the end of the last ice age. Note the Dansgaard-Oeschger events visible in the NGRIP core but barely, if at all, in the Antarctic cores. The period around 120 kyr is the previous interglacial; before that (140 kyr) is the previous glacial.
|
|
Chart Of
http://aa.usno.navy.mil/cgi-bin/aa_geocentric.pl |