Antarctica has a winter sea ice shortfall four times the size of Texas

Antarctica is missing over 1 million square miles of floating sea ice, even though it's currently the dead of winter in the Southern Hemisphere.

Why it matters: Scientists don't know what is driving the shortfall, but they are deeply concerned about its consequences, as sea ice influences the planet's climate, global ocean currents and marine ecosystems.

• The sea ice is still growing, but it's never been this low in 45 years of record-keeping. The shortfall is equivalent to nearly four times the area of Texas, according to the National Snow and Ice Data Center.
• To fill the gap, the sea ice would have to grow at unrealistic, record-breaking rates for the rest of the Southern Hemisphere's winter, Edward Doddridge, an oceanographer and research associate at the University of Tasmania, told Axios.

How it works: Sea ice in the Antarctic, which typically surrounds the icebound continent, is struggling to recover from vast melting during the summer.

• During the summer, ice extent plunged it to the lowest levels ever recorded since satellite observations began in the late 1970s.
• Floating sea ice in the Arctic and the Antarctic grows and shrinks with the seasons in both the Northern and Southern Hemispheres.
• In the Antarctic, sea ice extent — or the area of ocean where at least 15% of the surface is frozen — reaches its nadir in summer between February and March before reforming in the winter, and hits its growth peak between September and October.
• Unlike in the Arctic, which has experienced dramatic sea ice loss over several decades from human-caused climate change, scientists actually observed a slight expansion in total sea ice around Antarctica between 1979 to 2014. But that expansion plateaued in 2015 before sea ice coverage began rapidly declining starting in 2016.

What they're saying: It's too early to determine to what extent climate change is responsible for this year's sea ice gap, but it can not be ruled out, Eric Rignot of NASA's Jet Propulsion Laboratory and the University of California, Irvine told Axios.

• Rignot said he believes the minor ice growth seen over previous decades was from warming and changes in the ozone hole creating stronger winds that pushed Antarctic sea ice to fan out across a larger area.
• He said it's possible that around 2016, the sea ice could no longer overcome warming in the Southern Ocean caused by climate change.
• When declines began in 2016, Rignot said scientists were unable to say whether it was an anomaly or part of a longer trend.
• "Now, we can say with a bit more certainty that this is not anomalous behavior — it's a change of state," Rignot said.

Threat level: The survival of many Antarctic species are intertwined with sea ice.

• Plankton and other forms of marine algae that are key to the carbon cycle and are the base of aquatic food chains greatly depend on sea ice in order to bloom throughout the year.
• Recent studies have estimated that sea ice loss is disrupting algae blooms in the Arctic, with potentially large consequences for food webs and biodiversity. Other studies have indicated that this disruption may already be happening near parts of Antarctica.

• If the sea ice doesn't bounce back, many animals — including crustaceans, fish, penguins, seals, sea lions and whales — that depend on it for breeding and feeding grounds and protection could be affected, Doddridge said.
• "We have never seen these species live in a world where the ice hasn't been fairly consistent, and we don't know if they can survive in a world where it isn't," Doddridge said, adding that he thinks that ocean warming from climate change is the predominant cause of the ice deficit.

Be smart: Sea ice melting only slightly affects sea level rise because it's already in the ocean.

• However, the deficit in sea ice can indirectly speed up sea level rise by allowing milder ocean waters to reach the land-based Antarctic ice sheet, promoting faster melting.
• The sea ice forms a barrier between warmer ocean waters and Antarctic ice shelves — the thick slabs of ice attached to land-based glaciers.
• Over the long term, decreased sea ice levels could also contribute to the observed slowing of water circulation in parts of the Southern Ocean, which power the world's deep ocean currents that drive heat, carbon, oxygen and nutrients around the world.

Context: Lettie Roach, an associate research scientist at the NASA Goddard Institute for Space Studies and Columbia University, said she finds it especially concerning to see the sea ice shortfall occurring at the same time as scorching heat is breaking global temperature records.

• The globe set a record for the warmest June since at least 1940, and scientists predict that July will be Earth's hottest month ever recorded.

Go deeper: Study: Key Atlantic Ocean circulation could shut down by mid-century