It is winter in the Southern Hemisphere, when ice typically
forms around Antarctica. But this year, that growth has been stunted, hitting a
record low by a wide margin.
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Alarming scientists and raising concerns about the vital role of
the ocean
The sharp drop in sea ice is alarming scientists and raising
concerns about its vital role in regulating ocean and air temperatures,
circulating ocean water and maintaining an ecosystem crucial for everything
from microscopic plankton to the continent’s iconic penguins.
“This year is really different,” said Ted Scambos, a senior
research scientist at the University of Colorado Boulder and an Antarctica
expert at the National Snow and Ice Data Center. “It’s a very sudden change.”
Global consequences to follow
A continued decline in Antarctic Sea ice would have global
consequences by exposing more of the continent’s ice sheet to the open ocean,
allowing it to melt and break off more easily, contributing to rising sea
levels that affect coastal populations around the world.
Less ice also means less protection
Less ice also means less protection from solar rays, which can raise
the water temperature, making it harder for ice to form.
At the end of June, ice covered 4.5 million square miles, or
11.7 million square kilometers, of ocean around the continent, according to
NSIDC data. That’s nearly 1 million square miles less than the expected average
from approximately 40 years of satellite observations.
The clear departure from previous years is startling, since sea
ice around Antarctica has been slower to respond to climate change than ice in
the Arctic Ocean.
Antarctic sea ice also set a record low in 2022, but this year’s
ice cover is almost 500,000 square miles smaller.
“The Antarctic Sea ice extent low in 2023 is unprecedented in
the satellite record,” Liping Zhang, a project scientist at the National
Oceanic and Atmospheric Administration’s Geophysical Fluid Dynamics Laboratory,
wrote in an email.
Scientists are still investigating this question
The record low might signal a shift in the sea ice system to a
new, unstable state where extremes become more common, but Zhang cautioned that
scientists are still investigating this question.
Sea ice around Antarctica typically freezes from February to
August and then melts until the next Southern Hemisphere winter. Several ocean
and atmosphere patterns influence how much ice grows or shrinks, and the
overlapping interactions between these forces are complicated.
On top of these natural, short-term patterns is the long-term
influence of humans burning fossil fuels that add greenhouse gases to the
atmosphere. Some researchers suspect that we are finally seeing the effects of
this slow burn on Antarctica’s previously resilient sea ice.
This year’s change, within the context of several years in a row
with less sea ice, is “very, very concerning,” said Marilyn Raphael, a
geography professor and director of the Institute of the Environment and
Sustainability at University of California, Los Angeles. “That is not within
natural variability,” she said.
Raphael has been working to extend the historical record of
Antarctic Sea ice past the 1970s, when satellite observations began. She and
her colleagues recently published a new data set going back to 1905, using
weather observations to reconstruct the extent of sea ice during earlier years.
While it is still limited data, the longer record captures more
cycles of natural variability. Raphael and other experts think that the ocean,
which warms up more slowly than the atmosphere and has absorbed much of the
heat from the burning of fossil fuels, may have reached a point where that heat
is affecting Antarctic Sea ice.
Sea surface temperatures have broken records this year, and
there are currently three patches of unusually warm water around Antarctica.
While other factors are also at play, these hot spots line up with the areas on
the coast where sea ice has been unusually slow to form, Scambos said.
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