Study Shows How Earth’s Orbit Affects Ice Ages

A recent study suggests the next ice age will likely begin in about 11,000 years unless emissions change the effects of natural climate cycles.

An ice age is a period of reduced temperatures causing ice to cover large areas of the northern and southern parts of the world.

A group of scientists studied changes in the shape of the Earth’s orbit around the sun, the tilt of the Earth’s axis and the movement of the axis itself, called a wobble. These three motions are believed to happen in cycles. The Serbian scientist Milutin Milankovitch developed a theory about 100 years ago that these cycles affected Earth’s long-term climate.

The team noted that small changes in Earth’s orbit around the Sun caused predictable cycles of warming and cooling over a period of about 100,000 years.

These findings permitted the team to determine how the three factors of tilt, wobble, and the shape of Earth's orbit might have affected the Earth’s climate over the last 900,000 years.

The group published its findings in Science on February 27.

The scientists examined a million-year record of climate by looking at ice sheets across the northern half of the world and deep ocean temperatures.

They then compared this data with small but regular changes in Earth’s orbit over time.

The lead writer of the study is Stephen Barker, a professor at Cardiff University in Britain. He told the French News Agency (AFP) that for many years it has been difficult for scientists to show exactly how small changes in Earth’s orbit have led to huge changes between warm and cold periods.

Earth is believed to go through cycles of ice ages and warm periods. The last ice age is thought to have ended around 11,700 years ago. Scientists, such as Milankovitch, have long seen a connection between Earth's orbit and climate.

However, researchers have struggled to precisely date when each of the climate changes happened. It has also been difficult for them to know exactly which orbit positions affect the start and stop of cold or warm periods.

Barker said his team of researchers studied slow changes in temperature over long periods of time instead of only looking at shorter periods of change between cold and warm climates.

Barker told AFP, "We would expect a glaciation to occur within the next 11,000 years, and it would end in 66,000 years' time."

Lorraine Lisiecki is a professor at the University of California, Santa Barbara, and a co-writer of the study. She said the study shows that changes in climate over tens of thousands of years are not random.

The team aims to expand its findings to investigate the long-term effects of human activity on climate. They also want to find out how it might affect Earth’s natural climate cycles.

I’m Andrew Smith.

Issam Ahmed wrote this story for Agence-France Presse. Andrew Smith adapted it for VOA Learning English.

emissions –plural n. gases released into the atmosphere

tilt –n. not straight up and down but set to the side at an angle

axis –n. the imaginary line around which the Earth revolves, or turns

cycle -n. an action or set of actions that repeat over a regular period

sheet -n. a flat, wide extent of a material such as paper or ice

precisely -adv. exactly

factor -n. something that affects a process or development

wobble -n. an apparently unsteady side-to-side motion

glaciation –n. a period in which large areas of ice form and move

random -adj. showing no particular order or period

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