By Tim Radford
They are different worlds, one an ocean, the other a continent. But a polar link keeps them in touch with each other.
LONDON, 30 November, 2020 − The Arctic and Antarctica are literally a world apart, but for an unlikely polar link. Change in the mass of ice in the north can and does precipitate change in the furthest reaches of the southern hemisphere.
According to 40,000 years of geological evidence, when the Arctic Ocean ice retreats, global sea levels rise to start washing away the sea ice around the shelf of the vast frozen continent at the other extreme of the planet.
This pattern of action at a distance is confirmed by computer simulations: the planet’s two hemispheres are in a kind of conversation, according to a new study in the journal Nature.
“Our results highlight how interconnected the Earth system is, with changes in one part of the planet driving changes in another,” said Natalya Gomez, of McGill University in Canada, who led the study.
“In the modern era, we haven’t seen the kind of large ice sheet retreat that we might see in our future warming world. Looking to records and models of change in Earth’s history can inform us about this.”
“Ice sheets can influence each other over great distances. It’s as though they were talking to one another about sea level changes”
Although both extremes of cold are vulnerable to global heating driven by profligate fossil fuel use and global-scale loss of forests, climate scientists have tended to consider them as separate cases.
But a closer look at geological records − ice cores and samples from the ocean bottom that offer evidence of iceberg drift across the millennia − revealed a connection. The polar link is real.
At the height of the last ice age more than 20,000 years ago, the mass of ice in the north lowered global sea levels and the Antarctic ice shelf advanced. As the world began to warm again, ice in the north began to flow into the sea. Sea levels rose in the southern hemisphere and this began to force a retreat of the Antarctic ice.
“Ice sheets can influence each other over great distances due to the water that flows between them. It’s as though they were talking to one another about sea level changes,” Dr Gomez said.
“Polar ice sheets are not just large static mounds of ice. They evolve on various different time scales and are in constant flux, with ice growing and retreating, depending on the climate and the surrounding water levels.
“They gain ice as snow piles up on top of them, then spread outwards under their own weight, and stream out into the surrounding ocean where their edges break off into icebergs.”
The evidence showed that sea level change in Antarctica and ice mass loss in the Arctic were linked, over a sequence of at least 40,000 years.
“These ice sheets are really dynamic, exciting and intriguing parts of the Earth’s climate system. It’s staggering to think of ice that is several kilometres thick, that covers an entire continent, and that is evolving on all of these different timescales with global consequences,” Dr Gomez said.
“It’s just motivation for trying to better understand these really massive systems that are so far away from us.” − Climate News Network