Rising sea levels lengthen Earth’s days at unprecedented rate

Electric Time Co. employee Walter Rodriguez cleans the face of an 84-inch Wegman clock at the plant in Medfield, Mass. Thursday, Oct. 30, 2008. (AP Photo/Elise Amendola)

A new study suggests climate change is doing something few people would ever notice: it’s making the days on Earth slightly longer.

Researchers say rising sea levels caused by melting ice are slowing the planet’s rotation, stretching the length of day by tiny fractions of a second.

While the change is almost impossible to feel in daily life, scientists say the rate at which it’s happening is unlike anything seen in millions of years.

The findings were published in the journal of Geophysical Research: Solid Research by scientists from the University of Vienna and ETH Zurich, a public university in Switzerland.

Why climate change affects the length of day

Earth doesn’t spin at a perfectly constant speed. Its rotation can change due to several factors, the study said, including the gravitational pull of the moon and movements inside the planet.

But modern climate change is now playing a role.

As global temperatures rise, glaciers and polar ice sheets are melting. That water flows into the oceans, adding to rising sea levels and redistributing mass around the planet, the study said.

The study explained that when a spinning figure skater stretches their arms outward, their spin slows down. Pulling their arms inward makes them spin faster.

Earth behaves in a similar way when mass moves outward — in this case from ice sheets to oceans — the planet’s rotation slows, according to the study.

Between 2000 to 2020, scientists estimate the length of a day increased at a rate of 1.33 milliseconds per century, due to climate-related changes.

Scientists look back millions of years

To understand whether this kind of change has happened before, researchers examined fossil evidence going back 3.6 million years.

They used the remains of tiny marine organisms called benthic foraminifera, single-celled creatures that live on the ocean floor.

The study said their shells preserve chemical clues about past ocean conditions. By studying those chemical signatures, scientists can estimate ancient sea levels.

From those sea-level changes, the team was able to calculate how Earth’s rotation likely changed over time.

To analyze the complex data, the researchers also used a physics-informed, deep-learning model, a type of artificial intelligence that incorporates known physical laws to better interpret uncertain climate records.

Where today ranks in Earth’s history

The analysis shows that natural cycles of ice growth and melting during the past 2.6 million years — a period known as the Quaternary — did cause day-length changes in the past.

However, the modern rate of change is unusually fast.

The changes themselves are extremely small — just milliseconds, the study suggested.

But even tiny shifts in the Earth’s rotation matter for technologies that rely on extremely precise timing. For example, systems used in space navigation, satellite tracking and astronomical measurements must account for small variations in how fast Earth spins.

Researchers said that by the end of this century, climate change could influence the planet’s rotation more strongly than the moon, which has historically been the main factor in slowing Earth’s spin over long periods.

According to the study, this research is one of the first to connect ancient climate records with modern changes in Earth’s rotation.

Even if the difference is measured in milliseconds, scientists say it’s another signal of how profoundly the planet’s climate system is shifting.