Information about Orbital Forcing
Orbital forcing describes the effect on climate of slow changes in the tilt of the Earth's axis and shape of the orbit (see Milankovitch cycles). These orbital changes change the total amount of sunlight reaching the Earth by up to 25% at mid-latitudes (from 400 to 500 Wm-2 at latitudes of 60 degrees). In this context, the term "forcing" signifies a physical process that affects the Earth's climate.
This mechanism is believed to be responsible for the timing of the ice age cycles. A strict application of the Milankovitch theory does not allow the prediction of a "sudden" ice age (rapid being anything under a century or two), since the fastest orbital period is about 20,000 years. The timing of past glacial periods coincides very well with the predictions of the Milankovitch theory, and these effects can be calculated into the future.
It is sometimes asserted that the length of the current interglacial temperature peak will be similar to the length of the preceding interglacial peak (Sangamon/Eem), and from this conclude that we might be nearing the end of this warm period. However, this conclusion is probably mistaken: the lengths of previous interglacials were not particularly regular (see graphic at right). Berger and Loutre [1] argue that with or without human perturbations, the current warm climate may last another 50,000 years. The reason is a minimum in the eccentricity of Earth's orbit around the Sun. Also, Archer (2005) reports that probable future CO2 emissions may be enough to suppress the glacial cycle for the next 500 kyr.
Note in the graphic the strong 100,000 year periodicity of the cycles, and the striking asymmetry of the curves. This asymmetry is believed to result from complex interactions of feedback mechanisms. It has been observed that ice ages deepen by progressive steps, but the recovery to interglacial conditions occurs in one big step.
Orbital mechanics require that the length of the seasons be proportional to the swept 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. Today, when fall and winter in the northern hemisphere occur at closest approach, the earth is moving at its maximum velocity and therefore fall and winter are slightly shorter than spring and summer.
Today, summer is 4.66 days longer than winter and spring is 2.9 days longer than fall (source). As axial precession changes the place in the Earth's orbit where the solstices and equinoxes occur, winters will get longer and summers will get shorter, eventually creating conditions believed to be favorable for triggering the next ice age.
The arrangements of land masses on the Earth's surface are believed to reinforce the orbital forcing effects. Comparisons of plate tectonic continent reconstructions and paleoclimatic studies show that the Milankovitch cycles have the greatest effect during geologic eras when landmasses have been concentrated in polar regions, as is the case today. Greenland, Antarctica, and the northern portions of Europe, Asia, and North America are situated such that a minor change in solar energy will tip the balance between year-round snow/ice preservation and complete summer melting. The presence of snow and ice is a well-understood positive feedback mechanism for climate.
North America is a continent [1] in the Earth's northern hemisphere and (chiefly) western hemisphere. It is bordered on the north by the Arctic Ocean, on the east by the North Atlantic Ocean, on the southeast by the Caribbean Sea, and on the south and west
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This mechanism is believed to be responsible for the timing of the ice age cycles. A strict application of the Milankovitch theory does not allow the prediction of a "sudden" ice age (rapid being anything under a century or two), since the fastest orbital period is about 20,000 years. The timing of past glacial periods coincides very well with the predictions of the Milankovitch theory, and these effects can be calculated into the future.
)
Ice core data. Note length of glacial cycles averages ~100,000 years. Blue curve is temperature, green curve is CO2, and red curve is windblown glacial dust (loess). Today's date is on the left side of the graph.
Note in the graphic the strong 100,000 year periodicity of the cycles, and the striking asymmetry of the curves. This asymmetry is believed to result from complex interactions of feedback mechanisms. It has been observed that ice ages deepen by progressive steps, but the recovery to interglacial conditions occurs in one big step.
Orbital mechanics require that the length of the seasons be proportional to the swept 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. Today, when fall and winter in the northern hemisphere occur at closest approach, the earth is moving at its maximum velocity and therefore fall and winter are slightly shorter than spring and summer.
)
The length of the seasons is proportional to the area of the Earth's orbit swept between the solstices and equinoxes.
The arrangements of land masses on the Earth's surface are believed to reinforce the orbital forcing effects. Comparisons of plate tectonic continent reconstructions and paleoclimatic studies show that the Milankovitch cycles have the greatest effect during geologic eras when landmasses have been concentrated in polar regions, as is the case today. Greenland, Antarctica, and the northern portions of Europe, Asia, and North America are situated such that a minor change in solar energy will tip the balance between year-round snow/ice preservation and complete summer melting. The presence of snow and ice is a well-understood positive feedback mechanism for climate.
References
- Archer, D. and A. Ganopolski (2005), A Movable Trigger : Fossil Fuel Co2 And The Onset Of The Next Glaciation, Geochemistry Geophysics Geosystems 6 : Art . No . Q05003 May 5 2005
- The NOAA page on Climate Forcing Data includes (calculated) data on orbital variations over the last 50 million years and for the coming 20 million years
- The orbital simulations by Varadi, Ghil and Runnegar (2003) provide another, slightly different series for orbital eccentricity
Further reading
- J.D Hays, John Imbrie, and N.J. Shackleton, "Variations in the Earth's Orbit: Pacemaker of the Ice Ages," Science, 194, no. 4270 (1976), 1121-1132.
- Hays, James D., 1996: Encyclopedia of Weather and Climate, Oxford University Press, Stephen H. Schneider, ed. pp 507-508.
- Lutgens, Frederick K. and Edward J. Tarbuck, 1998: The Atmosphere, Prentice-Hall, Inc., 434pp.
- National Research Council, Solar Variability, Weather, and Climate, Washington, D.C.: National Academy Press, 1982, p. 7.
Climate is the average and variations of weather over long periods of time. Climate zones can be defined using parameters such as temperature and rainfall.
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EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001. Their greatest hit, their debut single "time after time", peaked at #13 in the Oricon singles chart.
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ORBit is a CORBA compliant Object Request Broker (ORB). The current version is called ORBit2 and is compliant with CORBA version 2.4. It is developed under the GPL license and is used as middleware for the GNOME project.
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Milankovitch cycles are the collective effect of changes in the Earth's movements upon its climate, named after Serbian civil engineer and mathematician Milutin Milanković.
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ice age is a period of long-term reduction in the temperature of Earth's climate, resulting in an expansion of the continental ice sheets, polar ice sheets and mountain glaciers.
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The Eemian interglacial era (known as the Sangamon interglacial in North America, the Ipswichian interglacial in the UK, and the Riss-Würm interglacial in the Alps) is the second-to-latest interglacial era of the Ice Age. It began about 131,000 years ago.
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100,000 year problem is a discrepancy between the climate response (as measured by proxies for the temperature and extent of glaciations) and the forcing from the amount of incoming solar radiation, or insolation, which has little power on a 100,000 year (
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Precession refers to a change in the direction of the axis of a rotating object. In physics, there are two types of precession, torque-free and torque-induced, the latter being discussed here in more detail.
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Plate tectonics (from Greek τέκτων, tektōn "builder" or "mason") is a theory of geology that has been developed to explain the observed evidence for large scale motions of the Earth's lithosphere.
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A geologic era is a subdivision of geologic time that divides an Eon into smaller buckets. The Phanerozoic Eon is divided into three such timeframes: the Paleozoic, Mesozoic, and Cenozoic represent the major stages in the macroscopic fossil record.
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Nunarput utoqqarsuanngoravit
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Europe is one of the seven traditional continents of the Earth. Physically and geologically, Europe is the westernmost peninsula of Eurasia, west of Asia. Europe is bounded to the north by the Arctic Ocean, to the west by the Atlantic Ocean, to the south by the Mediterranean Sea,
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Asia is the world's largest and most populous continent. It covers 8.6% of the Earth's total surface area (or 29.4% of its land area) and, with almost 4 billion people, it contains more than 60% of the world's current human population.
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North America is a continent [1] in the Earth's northern hemisphere and (chiefly) western hemisphere. It is bordered on the north by the Arctic Ocean, on the east by the North Atlantic Ocean, on the southeast by the Caribbean Sea, and on the south and west
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