Milankovitch Oscillation and Climate Change

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Introduction

Cycles have a big impact on the Earth's short-term weather and its long-term climate. About a century ago, the Serbian scientist Milutin Milankovitch argued that slow, repeating changes in the Earth's orbit around the Sun add up over thousands of years and become a major driver of long-term climate. He linked these orbital changes to the start and end of glacial periods, better known as Ice Ages. These notes explain the three Milankovitch cycles in simple terms, and then look at why they matter for the climate debate happening right now. For more study notes like this, browse our Resources library.

What are the Milankovitch cycles?

There are three separate movements of the Earth, each running on its own clock. Together they change how much sunlight different parts of the Earth receive, and when they receive it:

Eccentricity: the shape of Earth's orbit around the Sun.
Obliquity: the angle at which Earth's axis is tilted.
Precession: the direction in which Earth's spin axis is pointed.

Eccentricity: the shape of Earth's orbit

The Earth's yearly orbit around the Sun is not a perfect circle, but it comes close. The gravity of our solar system's two largest gas giants, Jupiter and Saturn, slowly pulls the shape of Earth's orbit from nearly circular to slightly elliptical and back again. Eccentricity is simply a measure of how far the orbit strays from a perfect circle, and it completes a cycle about every 100,000 years. These changes affect the distance between the Earth and the Sun. Even so, the eccentricity cycle has only a small effect on the total sunlight the Earth receives in a year, so its role in yearly seasonal changes is modest.

Obliquity: the tilt of Earth's axis

Obliquity is the angle at which the Earth's axis of rotation is tilted as the planet travels around the Sun. This tilt is the reason we have seasons at all. Over the past million years the angle has moved between 22.1 and 24.5 degrees, in a cycle that lasts about 41,000 years. The bigger the tilt, the more intense the seasons, because each hemisphere gets more solar energy in summer, when it leans towards the Sun, and less in winter, when it leans away. Larger tilt angles tend to encourage deglaciation, which is the melting and retreat of glaciers and ice sheets. This effect is not the same everywhere: higher latitudes, near the poles, see a much larger change in total solar energy than places near the equator.

The Earth's axis is currently tilted at 23.4 degrees, roughly halfway between its two extremes, and the angle is slowly decreasing. As obliquity shrinks, it gently makes our seasons milder, giving warmer winters and cooler summers. Over long stretches of time this lets snow and ice build up into huge ice sheets at high latitudes. As the ice cover grows, more of the Sun's radiation is reflected back into space, which cools the planet even further.

Precession: the wobble of Earth's axis

As the Earth spins, its axis wobbles slightly, much like a spinning top that is a little off-centre. This wobble is caused by the pull of the Sun and the Moon on the Earth's equatorial bulge. Axial precession describes how the direction of this wobble slowly changes compared with the fixed positions of the stars. Today the Earth's northern axis points close to Polaris, our current North Star, but a few thousand years ago it pointed towards different stars, Kochab and Pherkad. The axial precession cycle lasts about 25,771.5 years.

As the Earth moves through a precession cycle, the way the planet is angled changes with respect to perihelion and aphelion. Perihelion is the point where the Earth is closest to the Sun, and aphelion is where it is furthest. If a hemisphere is tilted towards the Sun during perihelion, it will be tilted away during aphelion, and the opposite is true for the other hemisphere. The hemisphere that faces the Sun at perihelion and away at aphelion ends up with sharper differences between its seasons.

At the moment, the southern hemisphere has its summer near perihelion and its winter near aphelion, which is why the southern hemisphere currently has more extreme seasons than the northern hemisphere. Because of precession, seasonal contrasts slowly grow stronger in one hemisphere and weaker in the other.

How the three cycles work together

No single cycle acts alone. Eccentricity, obliquity and precession overlap, sometimes adding up and sometimes cancelling out. When their combined effect reduces summer sunlight at high northern latitudes, snow survives from one year to the next, ice sheets grow, and the planet slides into an Ice Age. When the pattern reverses and summers become stronger, the ice melts and a warmer interglacial period begins. This is why the Milankovitch cycles are often called the pacemaker of the Ice Ages.

Why it still matters today

The Milankovitch cycles are the natural, long-term rhythm of Earth's climate. But they are also at the centre of a live argument in today's climate debate. Some people claim that the warming we see now is "just a natural cycle." The science says otherwise, and the reason is all about speed and timing. You can explore the wider topic in our Learnacy Hub and in more Geography notes.

Milankovitch cycles work over tens of thousands to hundreds of thousands of years. The warming happening now has taken place over just decades and centuries, far too fast for orbital changes to cause. In fact, NASA points out that if humans had no influence on the climate, Earth's current orbital position should be slowly cooling the planet, not warming it, continuing a gentle cooling trend that began around 6,000 years ago.

Instead, the planet is heating up. NASA's climate models show that any nudge from the Milankovitch cycles is overwhelmed once carbon dioxide in the atmosphere passes about 350 parts per million, which it already has. Since 1750, the warming from greenhouse gases released by burning fossil fuels is over 50 times greater than the tiny extra warming from the Sun over the same period.

The numbers make this clear. According to the Copernicus Climate Change Service and the World Meteorological Organization, 2024 was the warmest year on record and the first full calendar year with a global average temperature about 1.55 degrees Celsius above the 1850 to 1900 pre-industrial level. The ten warmest years on record are all within the last decade.

If there were no human influences on climate, scientists say Earth's current orbital positions predict our planet should be cooling, not warming. (NASA)

So the Milankovitch cycles are not a rival explanation for modern warming. They are the slow natural background, and right now that background is pointing gently towards cooling. The rapid warming on top of it is the human-made part, driven by the greenhouse gases we are adding to the air.

Quick revision

Eccentricity is the shape of the orbit, on a roughly 100,000 year cycle, with a small effect.
Obliquity is the axial tilt, moving between 22.1 and 24.5 degrees on a 41,000 year cycle, and it controls how strong the seasons are.
Precession is the wobble of the axis, on a roughly 25,771 year cycle, deciding which hemisphere gets the most extreme seasons.
Together the cycles pace the Ice Ages, but they are far too slow to explain today's rapid, human-driven warming.

Sources

Key takeaways

Milutin Milankovitch proposed that slow, repeating changes in Earth's orbit around the Sun drive long-term climate and the timing of Ice Ages.
The three Milankovitch cycles are eccentricity (orbit shape), obliquity (axis tilt), and precession (axis wobble), each running on its own clock.
These cycles change how much sunlight different parts of Earth receives and when, working together to trigger Ice Ages when they reduce summer sunlight at high northern latitudes.
Current global warming happens over decades and centuries, far too fast for orbital changes which operate over tens of thousands to hundreds of thousands of years.
NASA states that without human influence, Earth's current orbital position should be slowly cooling the planet, but greenhouse gases have overwhelmed any natural orbital effect.

Test yourself

What are the three Milankovitch cycles?

Eccentricity, obliquity, and precession.

How long do the Milankovitch cycles take to complete?

They work over tens of thousands to hundreds of thousands of years.

What should Earth's orbital position be doing right now according to NASA?

Slowly cooling the planet, continuing a gentle cooling trend that began around 6,000 years ago.

Frequently asked questions

What are the three Milankovitch cycles, and how do they differ from one another?

The three Milankovitch cycles are eccentricity (shape of Earth's orbit), obliquity (tilt of Earth's axis), and precession (wobble of Earth's axis). Each cycle operates on a different timescale and alters how much sunlight Earth receives or when it is received, with eccentricity cycling every ~100,000 years, obliquity every ~41,000 years, and precession every ~25,771.5 years.

Why does Earth's orbital shape (eccentricity) have only a modest effect on yearly sunlight despite changing the distance to the Sun?

Eccentricity alters Earth's distance from the Sun, but the total sunlight Earth receives in a year changes only slightly because the variations in distance are relatively small compared to the overall solar energy received.

How does the tilt of Earth's axis (obliquity) influence the intensity of seasons?

A greater tilt angle intensifies seasonal differences because each hemisphere receives more solar energy in summer when tilted toward the Sun and less in winter when tilted away. This effect is strongest near the poles, where solar energy changes are most pronounced.

What is axial precession, and how does it affect climate over long periods?

Axial precession is the slow wobble of Earth's axis, which changes the direction the axis points relative to fixed stars over ~25,771.5 years. This alters the timing of seasons by shifting when Earth is closest or farthest from the Sun, indirectly influencing long-term climate patterns.

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