Milankovitch cycles

Also called: Milankovitch oscillations · Topic: Climate Change: Causes, Evidence and the Global Response · NCERT: Class 11, Ch 11 "World Climate and Climate Change"

Meaning

Milankovitch cycles (Class 11 spells it "Millankovitch oscillations") are slow, regular changes in three things. These are the shape of the Earth's orbit, the tilt of its axis, and the wobble of that axis. Together they change how much insolation (incoming sunlight energy) the Earth gets, and where and when it falls.

• They matter because they are seen as the main pacemaker (the regular beat) of the glacial cycles (ice ages) of the last several million years [2].
• They act over thousands of years, so they cannot explain the warming since the Industrial Revolution.

Explanation

The three cycles

• The cycles are named after Milutin Milanković, a Serbian scientist. He worked on them from about 1920 to 1941.
• They are an astronomical cause of climate change. This means the cause comes from outside the Earth, from the Earth's path around the Sun.

Cycle	What changes	Range	Period
Eccentricity	Shape of the orbit, from nearly circular to slightly oval	about 0 to 0.06 [2]	about 100,000 and 413,000 years
Obliquity	Axial tilt: the angle of the Earth's axis to its orbit	22.1°–24.5°; now 23.44° and falling	about 41,000 years
Precession	Wobble of the axis, like a spinning top	—	about 26,000 years for the axis; about 19,000–23,000 years when combined with the turning of the orbit ("climatic precession") [2]

What each cycle changes

• Eccentricity changes the total sunlight the Earth gets over a year [2].
• Obliquity and precession change two other things [2]:
• where the sunlight falls (which latitudes)

• when it falls (which season)

• Obliquity in simple terms:

• A bigger tilt gives hotter summers and colder winters.
• A smaller tilt gives milder seasons.
• Today the tilt is 23.44° and falling, so the seasons are slowly becoming milder.

How a small orbital push becomes an ice age

• Step 1: weak summer sunlight in the far north
• Summer sunlight at high northern latitudes becomes weaker.
• Winter snow does not melt fully.

• Snow builds up year after year, and ice sheets grow.

• Step 2: the ice-albedo feedback

• Albedo means how much light a surface reflects.

• White ice reflects more sunlight back to space, so the Earth cools further.

• Step 3: the CO₂ feedback

• Colder oceans hold more CO₂.

• Less CO₂ in the air means less greenhouse warming, so the Earth cools still more.

• Result: these feedbacks (effects that strengthen the cause that started them) make the small orbital push much stronger. Ice ages begin. When the push reverses, ice ages end.

The key limit

• The cycles work over thousands of years, not decades.
• So they cannot explain the warming seen since the Industrial Revolution.

Where it occurs

• Whole Earth: the cycles change the orbit and axis of the entire planet. So they affect climate everywhere, not one region.
• High northern latitudes: this is the key zone for the theory. Weak summer sunlight here lets ice sheets grow.
• In time: they paced the glacial cycles (ice ages) of the last several million years [2].
• India and the world today: they are slow natural changes in the background. They do not drive present-day warming, which comes from human greenhouse gases.
• In NCERT: Class 11, Ch 11 "World Climate and Climate Change" lists them under the astronomical causes of climate change, next to sunspots.

Don't confuse with

• Sunspot (solar) cycle: this is also an astronomical cause, but it is a change in the Sun's own output over about 11 years. Milankovitch cycles are changes in the Earth's orbit and axis, and they take tens of thousands of years.
• Obliquity vs precession: obliquity is a change in the angle of the tilt (22.1°–24.5°, about 41,000 years). Precession is a change in the direction the axis points, a wobble like a spinning top (about 26,000 years). The angle does not change during precession.
• Volcanic cooling: this is a terrestrial cause (it comes from the Earth itself). Volcanic sulphate aerosols cool the Earth for only a few years. Milankovitch cycles act over millennia.
• Anthropogenic (human-caused) warming: this works over decades to centuries and comes from greenhouse gases. Milankovitch cycles are far too slow to explain it.

Prelims Hooks

• Match the cycles: eccentricity – orbit shape – about 100,000 years; obliquity – axial tilt – about 41,000 years; precession – wobble – about 26,000 years.
• Ordering by period (longest first): eccentricity (about 100,000) > obliquity (about 41,000) > precession (about 26,000).
• Earth's tilt ranges from 22.1° to 24.5°. It is now 23.44° and decreasing.
• Trap: only eccentricity changes the total yearly sunlight. Obliquity and precession mainly change how it is spread over latitudes and seasons [2].
• Named after Milutin Milanković (Serbian). The cycles are an astronomical, not terrestrial, cause of climate change.
• Trap: "Milankovitch cycles explain post-industrial warming" is wrong, because they act over thousands of years.

Mains Points

• Natural causes cannot explain modern warming (GS-I / GS-III attribution):
• Milankovitch cycles act over millennia, not decades.
• Solar output has stayed flat or fallen a little since 1950, while temperatures rose sharply.

• This leaves human greenhouse gases as the main cause. IPCC AR6 (2021) says human influence on warming is "unequivocal" (beyond doubt).

• Feedbacks show that the climate system is sensitive:

• A small orbital change, made stronger by the ice-albedo and CO₂ feedbacks, was enough to start and end ice ages.

• So even about 1 °C of human warming matters. It can set off similar feedbacks, such as melting ice reducing albedo.

• Value for understanding past climates: the cycles explain the regular rhythm of ice ages in the Earth's history. This helps scientists separate slow natural change from today's fast, human-made change.

Related concepts

• Causes of climate change
• Sunspots
• Volcanism and climate

Read more

• Causes of climate change: astronomical and terrestrial