The calving front of the Pine Island Glacier, seen by a NASA aircraft in 2016. Image: NASA IceBridge.

An iceberg about five times the size of Manhattan has broken off the Pine Island Glacier in West Antarctica over the past 24 hours, an ominous sign of the continued retreat of this fast-flowing mass of ice. Like many other marine terminating glaciers in Antarctica, this glacier is retreating over time, and increasing the movement of ice into the sea.

Why it matters: While this iceberg itself is not record-breaking — it ranks as the sixth-largest iceberg to break off the Pine Island Glacier since 2001 — it illustrates the continued instability of marine-terminating glaciers in parts of the icebound continent.

The details: The iceberg had first appeared as a rift across Pine Island Glacier in September, before leading to the calving of about 300 square kilometers, or 116 square miles, of ice. The largest individual iceberg measures about 226 square kilometers in area, or 87 square miles.

Stef Lhermitte, a geoscientist at the Netherlands' Delft University of Technology who closely tracks Antarctic ice, tweeted that the glacier front, where the ice meets the sea, has now receded by about 5 kilometers, or close to a mile inland compared to recent decades.

  • Ice shelves, such as the one at the Pine Island Glacier, act like door stops to the land-based ice behind it. Once they diminish, due to a combination of warming from the ocean below and air temperatures above, it's more likely that inland ice will collapse into the sea, raising global sea levels.

Determining the amount of future ice loss from Antarctica is the biggest source of uncertainty in sea level rise projections, but recent studies have suggested that Antarctic ice melt is likely to be at the higher end of the scale.

  • Recent research published in Nature Climate Change, found that "ice losses from Antarctica have accelerated during the past 25 years," and that 40% of the continent's sea level rise contribution has occurred during just the past 5 years.
  • Antarctica lost 1,883 billion tons of ice between 2007 and 2017, which was significantly higher than scientists estimated in a seminal report published in 2013.

The bottom line: The new iceberg is significant for reflecting trends taking place around Antarctica, which many climate scientists find worrisome.

Go deeper: West Antarctic ice melt poses unique threat to U.S., Antarctica has lost nearly 3 trillion tons of ice since 1992

Go deeper

Grand jury indicts ex-officer who shot Breonna Taylor for wanton endangerment

A memorial to Breonna Taylor in downtown Louisville, Kentucky on Sept. 23. Photo: Jeff Dean/AFP via Getty Images

A grand jury has indicted Brett Hankison, one of the Louisville police officers who entered Breonna Taylor's home in March and shot her at least eight times, on three counts of wanton endangerment.

The state of play: None of the three officers involved in the botched drug raid will face charges related to the actual death of Taylor, such as homicide or manslaughter.

FDA chief vows agency will not accept political pressure on coronavirus vaccine

Food and Drug Administration Commissioner Stephen Hahn promised that "science will guide our decision" for a coronavirus vaccine at a Senate hearing on Wednesday.

Why it matters: More Americans are expressing doubt about a first-generation vaccine, despite President Trump's efforts to push an unrealistic timeline that conflicts with medical experts in his administration.

CEO confidence rises for the first time in over 2 years

Data: Business Roundtable; Chart: Naema Ahmed/Axios

A closely-watched CEO economic confidence index rose for the first time after declining for nine straight quarters, according to a survey of 150 chief executives of the biggest U.S. companies by trade group Business Roundtable.

Why it matters: The index, which still remains at a decade low, reflects corporate America's expectations for sales, hiring and spending — which plummeted amid uncertainty when the pandemic hit.

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