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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

2 hours ago - World

Special report: Trump's U.S.-China transformation

Illustration: Aïda Amer/Axios

President Trump began his term by launching the trade war with China he had promised on the campaign trail. By mid-2020, however, Trump was no longer the public face of China policy-making as he became increasingly consumed with domestic troubles, giving his top aides carte blanche to pursue a cascade of tough-on-China policies.

Why it matters: Trump alone did not reshape the China relationship. But his trade war shattered global norms, paving the way for administration officials to pursue policies that just a few years earlier would have been unthinkable.

McConnell: Trump "provoked" Capitol mob

Senate Majority Leader Mitch McConnell (R-Ky.) said on Tuesday that the pro-Trump mob that stormed the U.S. Capitol on Jan. 6 was "provoked by the president and other powerful people."

Why it matters: Trump was impeached by the House last week for "incitement of insurrection." McConnell has not said how he will vote in Trump's coming Senate impeachment trial, but sources told Axios' Mike Allen that the chances of him voting to convict are higher than 50%.

3 hours ago - Politics & Policy

GOP leaders skip Trump sendoff in favor of church with Biden

House Speaker Nancy Pelosi (D-Calif.), Senate Majority Leader Mitch McConnell (R-Ky.), Senate Minority Leader Chuck Schumer (D-N.Y.) and House Minority Leader Kevin McCarthy (R-Calif.) in July. Photo by Erin Scott-Pool/Getty Images

Congressional leaders, including House GOP leader Kevin McCarthy and Senate Majority Leader Mitch McConnell, will skip President Trump's departure ceremony in Maryland tomorrow morning in favor of attending mass with incoming President Joe Biden ahead of his inauguration, congressional sources familiar with their plans tell Axios.

Why it matters: Their decision is a clear sign of unity before Biden takes the oath of office.