What on Earth is Happening in Antarctica?

Things are changing in an unexpected way 9,300 miles from Washington DC

The hottest summer in recorded history is finally drawing to a close in the Northern Hemisphere. The US summer broke all kinds of records, with wildfires, drought, and extreme heat affecting nearly everyone. It may finally have convinced most Americans that climate change is neither happening to someone else nor happening sometime in the future. It's here, and it's now. 

In Antarctica, winter is ending. Right now, scientists are seeing the Antarctica winter enter uncharted territory. There's suddenly much less ice down there than their models would have predicted. We may be entering a phase shift, as the continent steps sharply into an era of low sea ice. Scientists are not exactly sure why these changes are happening, but they're worried. Government officials here in the US know that the consequences of melting in Antarctica for coastal cities on the East Coast of the US would be both profound and sudden. How profound, and how sudden, remains uncertain. Among the flurry of news stories about climate change around the world, this one may signal the greatest disruption of all.

Here's a graph that captures what's going on:

This graph is from a part of NASA called the National Snow and Ice Center, located at the University of Colorado in Boulder. (Nickname: "Snow and Ice.") 

We're used to large ups and downs with Antarctic sea ice, because each year about 15 million square kilometers of ice grows (over the Antarctic winter) and melts (in the Antarctic summer). The Snow and Ice graph shows that the reach of ice in Antarctica, its peak in the depth of winter, has stayed pretty constant since Snow and Ice started measuring it using satellites in 1979.

You can see from the graph that before 2014 there was a slight increase in ice extent over the long term. But since 2014, the direction of the graph has changed, with record lows in 2017, 2022, and now 2023. Most of the measurements for months following 2016 have been below average. And the extent of winter growth this year was substantially less than scientists expected: For the first time since 1979, the maximum extent of sea ice in Antarctica is less than 17 million square kilometers (6.56 million square miles). That number is, in turn, about a million square kilometers (386,000 square miles) less than the previous record low, which was in 1986. That difference from 1986 is larger than the combined areas of Texas and Colorado. We don't know why ice increased before 2014, and we don't know why it's decreasing so rapidly now. 

Here's another view of this data, by Zack Labe (@ZLabe, a post-doc at Princeton):

There was some speedy growth in September, but the entire 2023 line is very far away from what we saw between 1979 and 2010.  And this:

You can hum this visual. It goes up, it goes down, it goes up, and then, wham, it really goes down and stays there.

Here's a picture from Snow and Ice showing what this low-level of sea ice looks like on the surface of the Earth as of about a week ago:

The orange line in the picture shows the average extent of ice on the same day, September 13, between 1981 and 2010.

Why is this important? Sea ice is already floating in the ocean, so if it melts it doesn't affect sea levels around the world. But it does buffer the ice that is attached to the land in the form of ice shelves, keeping those shelves from being struck by waves. Those floating ice shelves, in turn, are just extensions of the giant ice sheets that we also call continental glaciers. And the giant ice sheets of Antarctica hold more than two-thirds of the freshwater on the planet.

If the sea ice is on a quickly melting path, that means the ice shelves and ice sheets are at greater risk than scientists had thought. Ice sheets are on land, so if they melt they raise the level of the ocean. We do know that melting from ice sheets has accounted for most of the sea level rise around the world since 2006, and that sea level rise is accelerating rapidly. 

Scientists are particularly worried about the West Antarctic Ice Sheet.That glacier actually lies below sea level, and it's enormous. It is thinning, and NASA's satellite data show it has lost a significant amount of mass over the last 20 years—an average of about 121 gigatons a year.

One gigaton is a billion tons. One gigaton weighs the same as about 10,000 aircraft carriers or 200 million elephants. So 121 gigatons is a lot of mass to lose. Now, there is a lot of ocean, so even all that loss caused what sounds like a small amount of sea level rise: 0.4 millimeters per year. But if the entire West Antarctic Ice Sheet melted and became one with the ocean around it, the waters around the world would rise by five meters, or 16.4 feet.

GRACE and GRACE-FO (Gravity Recovery and Climate Experiment (2002-2017) and GRACE Follow-On (since 2018)) are the names of the satellites NASA runs that track ice mass in Antarctica daily. The Eastern Antarctic Ice Sheet and the Antarctic Peninsula Ice Sheet are also losing mass, but most of the loss is happening to the Western Antarctic Ice Sheet.

Here's a useful map showing the location of the glaciers on Antarctica. 

People are particularly interested in the Thwaites Glacier, which is part of the West Antarctic Ice Sheet. If the Thwaites Glacier, also known as the Doomsday Glacier, melted, sea levels around the world would climb by more than two feet. Thwaites is acting as a kind of natural dam, holding back ice lakes behind it.

So there is suddenly, unexpectedly, less sea ice. There seems to be a downward trend happening to the extent of that ice. There's a significant loss of mass in West Antarctica. Thwaites is being undermined by Southern Ocean water.

Indeed, all of this is being affected by the Southern Ocean, which surrounds Antarctica (and lies beneath the WAIS). It is a hard-working body of water, responsible for capturing 75 percent of the heat and 50 percent of the carbon absorbed by the world's oceans. 

Here's the thing scientists are particularly worried about: We know that the surface of the Southern Ocean is cooling just slightly at least in part because of this sea-ice-melting, mass-loss-flowing happening in West Antarctica. But deeper layers of the Southern Ocean are actually getting substantially warmer. And that warm water, less salty and less dense, is rising upward. "Upwelling" is the term scientists use. And maybe warm water from the north is mixing into the upper ocean layer. There's something going on in this energy transfer between the upper and lower ocean that scientists can't explain, and the upwelling may be now happening faster and having effects that are speeding the melting of the Antarctic ice.

Is this natural variability? Is this a regime change?

If you live in a city on a coast, including the East Coast of the US, this should interest you. If all these contingencies happen, and land ice in Antarctica starts to run away into the Southern Ocean, a dramatic increase in sea level rise rates could take place well before the end of this century.