Earth’s orbit controlled sea-level rise for millennia but now it’s driven by man-made climate change, study reaffirms

Earth’s history of glaciation far more complex than previously thought, according to researchers at Rutgers University, reports Louise Boyle

Male, Maldives: the entire country could be submerged by 2100 due to sea-level rise (Getty/iStock)

Current sea-level rise is linked to human activities and not changes in Earth’s orbit, according to a new study, reaffirming scientific consensus on the effects of human-induced climate change.

The new research found that in the last 66 million years, the planet had almost ice-free periods when carbon dioxide (CO2) levels were not much higher than today’s measurements. The research also discovered glacial periods in times previously believed to have been ice-free.

The study, conducted by a team from Rutgers University’s Department of Earth and Planetary Sciences, concluded that minor variations in Earth’s orbit was the controlling force on ice volume and fluctuations in sea levels for millennia – the same which cannot be said today.

There is scientific consensus that global climate change is unleashing unprecedented crises on the planet. Among the consequences are rising sea levels which risk catastrophic flooding.

In the US, high-tide flooding is nine times more frequent that 50 years ago along areas of the coastline, the National Oceanic and Atmospheric Administration says.

Even if we curb global warming to the ambitious 1.5C goal set out by the UN’s Intergovernmental Panel on Climate Change (IPCC), by the end of the century, global sea level will likely rise at least 12 inches.

“Our team showed that the Earth’s history of glaciation was more complex than previously thought,” said lead author Kenneth G Miller, a professor in the Department of Earth and Planetary Sciences in the School of Arts and Sciences at Rutgers University-New Brunswick.

“Although carbon dioxide levels had an important influence on ice-free periods, minor variations in the Earth’s orbit were the dominant factor in terms of ice volume and sea-level changes – until modern times.”

The study was published today in the journal Science Advances. The paper reconstructed the history of sea levels and glaciation based on deep-sea geochemistry data.

Glacial periods were discovered during periods from 48-34 million years ago when the Earth was previously thought to have been ice-free.

Periods of ice-free conditions, from 17-13 million years ago, occurred when the concentration of atmospheric carbon dioxide was not much higher than today.

“We demonstrate that although atmospheric carbon dioxide had an important influence on ice-free periods on Earth, ice volume and sea-level changes prior to human influences were linked primarily to minor variations in the Earth’s orbit and distance from the sun,” Mr Miller said.

Carbon dioxide – a greenhouse gas driving climate change – is currently at a record high, the UN reported this month.

Around 20,000 years ago, during the last glacial period, sea levels took their largest recorded decline of 400 feet – slightly more than the height of the Statue of Liberty.

Following this drop, sea levels steadily climbed by about a foot per decade until around 10,000 years ago when the pace slowed.

From 2,000 years ago until the beginning of the 20th century, sea levels were stable until human-driven climate change caused them to begin to rise.

Further research reconstructing sea-level changes prior to 48 million years ago will help determine the role of atmospheric CO2 in glaciation and the cause of the natural fall in atmospheric CO2 before humans, the study noted.