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Earth orbit changes linked to Antarctic warming that ended last ice age, study finds

For more than one-hundred years scientists have been aware that the planet’s ice ages are the result of the wobbling of the Earth’s orbit, which alters its orientation to the sun and impacts the quantity of sunlight extending to higher latitudes, especially the polar regions.

According a news release from the University of Washington, the Northern Hemisphere’s crowning ice age finished approximately 20,000 years ago, and most evidence has shown that the ice age in the Southern Hemisphere finished approximately 2,000 year later, indicating that the south was reacting to warming in the north. However, new research reveals that Antarctic warming started at least two, maybe even four, millennia earlier than previously believed.

Most prior evidence for Antarctic climate change has emerged out of ice cores drilled in East Antarctica, the highest and coldest part of the continent. However, a team of researchers examining a new ice core from West Antarctica discovered that warming in that region was well under way 20,000 years ago.

“Sometimes we think of Antarctica as this passive continent waiting for other things to act on it. But here it is showing changes before it ‘knows’ what the north is doing,” said lead corresponding author T.J. Fudge, a University of Washington doctoral student in Earth and space sciences.

The results come from an in-depth analysis of an ice core obtained from the West Antarctic Ice Sheet Divide, a region where there is very little horizontal flow of the ice so that data are acknowledged to be from a location that remained consistent over long periods.

The ice core is more than two miles deep and covers 68,000 years. So far, however, data have been examined only from layers extending back 30,000 years. Closer to the surface, one meter of ice covers one year, but at greater depths the yearlong layers are compacted to centimeters.

Fudge recognized the yearlong layers by placing two electrodes along the ice core to determine higher electrical conductivity linked to each summer season. Evidence of greater warming showed up in layers linked to 18,000 to 22,000 years ago, the start of the last deglaciation.

“This deglaciation is the last big climate change that that we’re able to go back and investigate,” Fudge noted. “It teaches us about how our climate system works.”

West Antarctica is divided from East Antarctica by a significant mountain range. East Antarctica has a much higher elevation and is liable to be a lot colder, though there is recent evidence that it is also warming.

Very quick warming in West Antarctica in recent decades has been recorded in previous research by Eric Steig, a University of Washington professor of Earth and space sciences. Steig’s laboratory generated the oxygen isotope data utilized in the study. The new data authenticate that West Antarctica’s climate is more powerfully influenced by regional conditions in the Southern Ocean than East Antarctica is.

“It’s not surprising that West Antarctica is showing something different from East Antarctica on long time scales, but we didn’t have evidence for that before,” Fudge noted.

Fudge pointed out that the warming in West Antarctica 20,000 years ago is not accounted for by an alteration in the Sun’s intensity. Instead, how the Sun’s energy was dispersed over the region was a much greater factor. The Sun’s energy not only warmed the ice sheet but also warmed the Southern Ocean that encircles Antarctica, especially during the summer months when more sea ice melting could transpire.

Alterations in the Earth’s orbit today are not a significant factor in the rapid warming that has been detected recently, according to Fudge.

“Earth’s orbit changes on the scale of thousands of years, but carbon dioxide today is changing on the scale of decades so climate change is happening much faster today,” Fudge posited.

The study’s findings are described in greater detail in the journal Nature.