Editing Orbital forcing

{{Short description|Effect on the Earth's climate from slow orbital changes}}
'''Orbital forcing''' is the effect on [[climate]] of slow changes in the tilt of the [[Earth]]'s axis and shape of the Earth's [[orbit]] around the Sun (see [[Milankovitch cycles]]). These orbital changes modify the total amount of sunlight reaching the Earth by up to 25% at mid-latitudes (from 400 to 500 W/(m<sup>2</sup>) at latitudes of 60 degrees).{{Citation needed|date=February 2019}} 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 (sudden 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.

Milankovitch cycles are also associated with environmental change during [[Greenhouse and icehouse Earth|greenhouse]] periods of Earth's climatic history. Changes in lacustrine sediments corresponding to the timeframes of periodic orbital cycles have been interpreted as evidence of orbital forcing on climate during greenhouse periods like the [[Early Paleogene]].<ref>{{cite journal |last1=Shi |first1=Juye |last2=Jin |first2=Zhijun |last3=Liu |first3=Quanyou |last4=Huang |first4=Zhenkai |last5=Hao |first5=Yunqing |date=1 August 2018 |title=Terrestrial sedimentary responses to astronomically forced climate changes during the Early Paleogene in the Bohai Bay Basin, eastern China |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018217301566 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=502 |pages=1–12 |doi=10.1016/j.palaeo.2018.01.006 |s2cid=134068136 |access-date=12 January 2023|url-access=subscription }}</ref> Notably, Milankovitch cycles have been theorised to be important modulators of biogeochemical cycles during [[oceanic anoxic event|oceanic anoxic events]], including the [[Toarcian Oceanic Anoxic Event]],<ref>{{cite journal |last1=Kemp |first1=David B. |last2=Coe |first2=Angela L. |last3=Cohen |first3=Anthony S. |last4=Weedon |first4=Graham P. |date=1 November 2011 |title=Astronomical forcing and chronology of the early Toarcian (Early Jurassic) oceanic anoxic event in Yorkshire, UK |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2011PA002122 |journal=[[Paleoceanography and Paleoclimatology]] |volume=26 |issue=4 |pages=1-17 |doi=10.1029/2011PA002122 |access-date=5 April 2023|doi-access=free }}</ref> the [[Mid-Cenomanian Event]],<ref name="CoccioniGaleottiMidCenomanianEvent">{{cite journal |last1=Coccioni |first1=Rodolfo |last2=Galeotti |first2=Simone |date=15 January 2003 |title=The mid-Cenomanian Event: prelude to OAE 2 |url=https://www.researchgate.net/publication/223718129 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=190 |pages=427–440 |doi=10.1016/S0031-0182(02)00617-X |access-date=22 January 2023}}</ref> and the [[Cenomanian-Turonian oceanic anoxic event|Cenomanian-Turonian Oceanic Anoxic Event]].<ref name="MitchellEtAl2008EPSL">{{cite journal |last1=Mitchell |first1=Ross N. |last2=Bice |first2=David M. |last3=Montanari |first3=Alessandro |last4=Cleaveland |first4=Laura C. |last5=Christianson |first5=Keith T. |last6=Coccioni |first6=Rodolfo |last7=Hinnov |first7=Linda A. |date=1 March 2008 |title=Oceanic anoxic cycles? Orbital prelude to the Bonarelli Level (OAE 2) |url=https://www.sciencedirect.com/science/article/abs/pii/S0012821X07007546 |journal=[[Earth and Planetary Science Letters]] |volume=267 |issue=1–2 |pages=1–16 |doi=10.1016/j.epsl.2007.11.026 |access-date=2 January 2023|url-access=subscription }}</ref><ref>{{cite journal |last1=Kuhnt |first1=Wolfgang |last2=Holbourn |first2=Ann E. |last3=Beil |first3=Sebastian |last4=Aquit |first4=Mohamed |last5=Krawczyk |first5=Tim |last6=Flögel |first6=Sascha |last7=Chellai |first7=El Hassane |last8=Jabour |first8=Haddou |date=11 August 2017 |title=Unraveling the onset of Cretaceous Oceanic Anoxic Event 2 in an extended sediment archive from the Tarfaya-Laayoune Basin, Morocco |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1002/2017PA003146 |journal=[[Paleoceanography and Paleoclimatology]] |volume=32 |issue=8 |pages=923-946 |doi=10.1002/2017PA003146 |access-date=5 April 2023|url-access=subscription }}</ref>

==Overview==
[[File:Vostok Petit data.svg|thumb|upright=1.75|Ice core data. Note length of glacial cycles averages ~100,000 years. Blue curve is temperature, green curve is CO<sub>2</sub>, and red curve is windblown glacial dust (loess). Today's date is on the right side of the graph.]]
It is sometimes asserted that the length of the current interglacial temperature peak will be similar to that of the preceding interglacial peak ([[Eemian Stage|Sangamonian/Eem Stage]]). Therefore, 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 (2002) 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.”<ref name="Berger2002">{{cite journal|last=Berger|first=A.|author2=Loutre, M. F.|title=An Exceptionally Long Interglacial Ahead?|journal=Science|date=23 August 2002|volume=297|issue=5585|pages=1287–1288|doi=10.1126/science.1076120|pmid=12193773|s2cid=128923481}}</ref> Also, Archer and Ganopolski (2005) report that probable future CO<sub>2</sub> emissions may be enough to suppress the glacial cycle for the next 500 kyr.<ref name="Archer2005">{{cite journal|last1=Archer|first1=David|author-link=David Archer (scientist)|last2=Ganopolski|first2=Andrey|title=A Movable Trigger: Fossil Fuel CO<sub>2</sub> And The Onset Of The Next Glaciation|journal=Geochemistry, Geophysics, Geosystems|date=5 May 2005|volume=6|issue=5|pages=Q05003|doi=10.1029/2004GC000891|bibcode=2005GGG.....6.5003A |doi-access=free}}</ref>

Note in the graphic, the strong [[100,000 year problem|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 in progressive steps. However, the recovery to interglacial conditions occurs in a single large 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 last substantially longer. Today, when autumn and winter in the Northern Hemisphere occur at closest approach, the Earth is moving at its maximum velocity and therefore autumn and winter are slightly shorter than spring and summer. 
[[File:SeasonDuration.png|400px|left|The length of the seasons is proportional to the area of the Earth's orbit swept between the solstices and equinoxes.]]
Today in the Northern Hemisphere, summer is 4.66 days longer than winter and spring is 2.9 days longer than autumn.<ref name="Benson2007">{{cite web|url=https://sites.google.com/site/bensonfamilyhomepage/Home/ice-age-and-global-warming|title=Global Warming, Ice Ages, and Sea Level Changes: Something new or an astronomical phenomenon occurring in present day?|last=Benson|first=Gregory|date=11 December 2007}}</ref> As [[axial precession]] changes the place in the Earth's orbit where the [[solstices]] and [[equinoxes]] occur, Northern Hemisphere winters will get longer and summers will get shorter, eventually creating conditions believed to be favourable for triggering the next glacial period.

The arrangements of land masses on the Earth's surface are believed to reinforce the orbital forcing effects. Comparisons of [[plate tectonic]] continent [[Plate reconstruction|reconstructions]] and paleoclimatic studies show that the [[Milankovitch cycles]] have the greatest effect during [[geologic era]]s 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 in the [[climate of the Arctic]], between [[Arctic ice pack|year-round snow/ice preservation]] and complete summer melting. The presence or absence of snow and ice is a well-understood [[positive feedback]] mechanism for climate.

==See also==
* {{slink|Paleocene–Eocene Thermal Maximum|Orbital forcing}}{{Broken anchor|date=2024-04-20|bot=User:Cewbot/log/20201008/configuration|target_link=Paleocene–Eocene Thermal Maximum#Orbital forcing|reason= The anchor (Orbital forcing) [[Special:Diff/1219844739|has been deleted]].}}{{Broken anchor|date=2024-04-20|bot=User:Cewbot/log/20201008/configuration|target_link=Paleocene–Eocene Thermal Maximum#Orbital forcing|reason= The anchor (Orbital forcing) [[Special:Diff/1219844739|has been deleted]].}}

==References==
{{Reflist|2}}

==Further reading==
{{Refbegin|2}}
* {{cite journal |last=Hays |first=J. D. |author2=Imbrie, John |author3=Shackleton, N. J.  |year=1976 |title=Variations in the Earth's Orbit: Pacemaker of the Ice Ages |journal=Science |volume=194 |issue=4270 |pages=1121–1132 |doi=10.1126/science.194.4270.1121 |pmid=17790893 |bibcode=1976Sci...194.1121H |s2cid=667291 }}
* {{cite book |last=Hays |first=James D. |editor=Schneider, Stephen H. |title=Encyclopedia of Weather and Climate |year=1996 |publisher=Oxford University Press |location=New York |isbn=0-19-509485-9 |pages=507–508 }}
* {{cite book |title=The Atmosphere. An Introduction to Meteorology |last=Lutgens |first=Frederick K. |author2=Tarbuck, Edward J. |year=1998 |publisher=Prentice-Hall |location=Upper Saddle River, N.J. |isbn=0-13-742974-6 }}
* {{cite book |title=Solar Variability, Weather, and Climate |author=National Research Council |year=1982 |publisher=National Academy Press |location=Washington, D.C. |isbn=0-309-03284-9 |page=7 }}
{{Refend}}

* Cionco, Rodolfo G., and Pablo Abuin. "On planetary torque signals and sub-decadal frequencies in the discharges of large rivers." Advances in Space Research 57.6 (2016): 1411–1425.
==External links==
* [http://www.ncdc.noaa.gov/paleo/forcing.html 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
* [https://web.archive.org/web/20060210012245/http://www.astrobiology.ucla.edu/OTHER/SSO/ The orbital simulations by Varadi, Ghil and Runnegar (2003)] provide another, slightly different series for orbital eccentricity

{{Global warming}}
{{Climate oscillations}}

[[Category:Climate forcing]]