Milankovitch cycles

Milankovitch cycles describe how changes in the Earth's movements affect its climate over thousands of years. These cycles are named after Milutin Milanković, a Serbian geophysicist and astronomer. He studied how the Earth's shape, tilt, and wobble change how much sunlight reaches different parts of the planet. This change in sunlight influences the Earth's weather patterns over long periods. Learning about Milankovitch cycles helps scientists understand past climate changes and predict future ones.

Past and future Milankovitch cycles via VSOP modelGraphic shows variations in five orbital elements: Axial tilt or obliquity (ε). Eccentricity (e). Longitude of perihelion (sin(ϖ)). Precession index (e sin(ϖ))Precession index and obliquity control insolation at each latitude: Daily-average insolation at top of atmosphere on summer solstice ( Q ¯ d a y {\textstyle {\overline {Q}}^{\mathrm {day} }} ) at 65° NOcean sediment and Antarctic ice strata record ancient sea levels and temperatures: Benthic forams (57 widespread locations) Vostok ice core (Antarctica)Vertical gray line shows present (2000 CE)

Earth movements

The Earth's rotation around its axis, and revolution around the Sun, change over time due to gravitational interactions with other bodies in the Solar System. These changes affect the climate.

The Earth's orbit shifts between nearly circular and slightly elliptical. When the orbit is more stretched out, the distance between the Earth and the Sun changes more during the year, affecting the amount of solar radiation. The tilt of the Earth's axis also changes a little, making seasons more extreme when the tilt is greater. Finally, the direction the Earth's axis points shifts over time, changing which part of the year the Earth is closest to the Sun.

Milankovitch studied how these movements change the amount and location of sunlight reaching the Earth. This affects the Earth's temperature, especially at 65° north where there is a lot of land. Land changes temperature faster than oceans, which stay cooler because of mixing in deeper waters. The large oceans also slow down changes in the Earth's average temperature.

Orbital eccentricity

Main article: Orbital eccentricity

The Earth's orbit is almost round but can be slightly stretched out. When it is more stretched, the distance from the Sun changes more, causing bigger changes in sunlight. The shape of the orbit changes mainly because of the gravity of Jupiter and Saturn.

Axial tilt (obliquity)

Main article: Axial tilt

Planets orbiting the Sun follow elliptical (oval) orbits that rotate gradually over time (apsidal precession). The eccentricity of this ellipse, as well as the rate of precession, are exaggerated for visualization.

The tilt of the Earth's axis changes between 22.1° and 24.5° over about 41,000 years. When the tilt is greater, seasons are more extreme, with warmer summers and colder winters. The current tilt is about halfway between these extremes.

Axial precession

Main article: Axial precession

The direction the Earth's axis points shifts over about 25,700 years. This means that over time, different stars appear to be the north star. This shift affects which season the Earth is closest to the Sun during.

Apsidal precession

Main article: Apsidal precession

The Earth's orbit also shifts its orientation in space over about 112,000 years. This change happens mainly because of the gravity of Jupiter and Saturn.

Orbital inclination

Main article: Orbital inclination

The angle of the Earth's orbit also changes over time, moving up and down relative to its current path. This movement has a cycle of about 70,000 years and affects the Earth's climate patterns.

Season durations
Year	Northern hemisphere	Southern hemisphere	Date (UTC)	Season duration
2005	Winter solstice	Summer solstice	21 December 2005 18:35	88.99 days
2006	Spring equinox	Autumn equinox	20 March 2006 18:26	92.75 days
2006	Summer solstice	Winter solstice	21 June 2006 12:26	93.65 days
2006	Autumn equinox	Spring equinox	23 September 2006 4:03	89.85 days
2006	Winter solstice	Summer solstice	22 December 2006 0:22	88.99 days
2007	Spring equinox	Autumn equinox	21 March 2007 0:07	92.75 days
2007	Summer solstice	Winter solstice	21 June 2007 18:06	93.66 days
2007	Autumn equinox	Spring equinox	23 September 2007 9:51	89.85 days
2007	Winter solstice	Summer solstice	22 December 2007 06:08

Theory constraints

Scientists study things from Earth, like ice and ocean water, to learn about past climates. Ice from Antarctica has tiny air bubbles that help us understand past temperatures. These studies show that changes in how much sunlight Earth gets affect its climate.

Research from deep-ocean samples and lake levels also helps prove these ideas. For example, rock samples from Arizona and New England show patterns that match changes in Earth’s orbit.

Tabernas Desert, Spain: Cycles can be observed in the colouration and resistance of different sediment strata

100,000-year issue

Main article: 100,000-year problem

Milankovitch thought that changes in Earth’s tilt had the biggest effect on climate, suggesting a 41,000-year cycle for ice ages. But later studies found that ice ages over the last million years happen every 100,000 years, matching changes in Earth’s orbit shape. Scientists have different ideas about why this happens.

Transition changes

Main article: Mid-Pleistocene Transition

From 1 to 3 million years ago, climate cycles followed a 41,000-year pattern. But after one million years ago, the pattern changed to a 100,000-year cycle. Scientists think this shift might be linked to changes in carbon dioxide levels and other natural processes.

420,000 years of ice core data from Vostok, Antarctica research station, with more recent times on the left

Interpretation of unsplit peak variances

Even the most precise climate records from the last million years don’t perfectly match the expected shape of Earth’s orbit changes. Some researchers think the records show a single 100,000-year cycle instead of two smaller cycles. However, this split has been observed in very old rock samples.

Unsynced stage five observation

Deep-sea samples show that a warm period called marine isotope stage 5 started 130,000 years ago, which is 10,000 years earlier than expected based on changes in sunlight from Earth’s orbit.

Present and future conditions

Past and future estimations of daily average insolation at top of the atmosphere on the day of the summer solstice, at 65° N latitude. The green curve is with eccentricity e hypothetically set to 0. The red curve uses the actual (predicted) value of e; the blue dot indicates current conditions (2000 CE).

Because we can predict how Earth's orbit changes, scientists can use models to guess future climate. However, there are two important things to remember: we don't fully understand how these orbit changes affect climate, and other factors like human actions that increase greenhouse gases can also play a big role in making the planet warmer.

One old model from 1980 said that a cooling trend that started about 6,000 years ago would keep going for the next 23,000 years. Another study suggests that sunlight at 65° North will get stronger in about 6,500 years, then weaken back to today's levels in about 16,000 years. For the next 100,000 years, Earth's orbit will change less, so the main effect will come from tilt changes. These changes won't be enough to start a new ice age in the next 50,000 years.

Other celestial bodies

Mars

Since 1972, scientists have wondered if the layers in Mars polar regions are linked to the planet's orbit and climate changes. In 2002, they found that the amount of ice in these layers changes with the amount of sunlight Mars receives in the summer at its north pole, much like climate changes on Earth. They also discovered that Mars' tilt changes every about 51,000 years, its wobble every about 120,000 years, and its orbit shape every 95 to 99 thousand years. Mars does not have a large moon to keep its tilt steady, so its tilt has varied a lot over time.

Outer Solar system

Saturn's moon Titan might have a cycle of about 60,000 years that could move the location of its methane lakes. Neptune's moon Triton has similar changes that could cause its solid nitrogen deposits to shift over very long periods.

Exoplanets

Scientists using computer models have studied how extreme tilts of planets might affect their climates. They found that while very high tilts could create big climate changes, this might not make a planet unable to support life. Most such planets could still allow simple and more complex life to develop.