Temperature records are falling around the world as a strong El Niño brews in the Pacific Ocean and summer rises in the Northern Hemisphere. The planet recently experienced the hottest day and hottest June ever recorded. But some of the most alarming heat right now is occurring far away from most of humanity in Antarctica, where it’s currently winter.

The World Meteorological Organization reported last week that sea ice is at record low levels around Antarctica, 17 percent below the average for this time of year. Sea ice expands and shrinks with the seasons and the ice around Antarctica is still growing, but at the slowest pace seen since satellite observation began in the 1970s.

World Meteorological Organization

“It’s not something that we should be comfortable with,” Marilyn Raphael, a professor of geography at the University of California Los Angeles who studies Antarctic sea ice, told Vox. “It shouldn’t be as warm as it is. If that warming continues, it will make things go akilter.”

While its residents include just a handful of scientists (and millions of penguins), Antarctica is extraordinarily important for the rest of the planet. It’s home to 90 percent of the world’s ice, which comprises 70 percent of Earth’s fresh water. Most of that ice is on land, upward of three miles thick, and if it all melted, it would raise global sea levels by 190 feet. Fortunately, such a grim scenario is unlikely, but ice melt at the South Pole is accelerating. For the one-third of humanity that lives within 60 miles of an ocean shoreline, that will reshape their incomes, their diets, and where they can live.

Antarctica is also fringed by sea ice, which is formed when the ocean freezes. It doesn’t change the overall amount of water in the ocean, but ice reflects sunlight while the darker water tends to absorb it, thereby heating up. As sea ice retreats, the ocean warms and drives more melting. Water also expands slightly as it warms, which contributes to sea level rise.

Beyond water levels, Antarctica shapes both ocean currents, which move nutrients around the globe to nourish fisheries, and circulation patterns in the atmosphere, which can shape clouds, temperatures, and rainfall on every continent.

But Antarctica continues to puzzle scientists. For years, it defied climate patterns seen in other parts of the world: its sea ice expanded for a period, and some of its regions cooled while the rest of the planet warmed. The harsh environment still makes it difficult to get an accurate read of what’s happening on the ground. And as the climate changes, rising average temperatures will have some of their most profound effects on Antarctica, which in turn will ripple through the sky and the sea around the world. So it behooves everyone on Earth to pay attention to what’s happening at the South Pole.

“The sea ice and atmosphere and ocean all talk to each other,” Jeremy Bassis, a professor of climate and space sciences at the University of Michigan, said. “We just haven’t quite seen the size of the changes that are coming.”

Why it’s so concerning that the South Pole is so hot

The air temperature in Antarctica is unusually high right now. Along the Antarctic peninsula, the bit that juts toward South America, it’s more than 18 degrees Fahrenheit warmer than average for this time of year. Normally it’s about 14 degrees Fahrenheit.

Climate Reanalyzer

That’s still pretty chilly, especially compared to the weather up north, but it’s enough to alter air circulation patterns. The sea surface temperature around Antarctica is strangely warm as well. According to David Schneider, a research scientist at the National Center for Atmospheric Research and at the University of Colorado Boulder, that’s what matters most for sea ice. “If you look at maps of where the sea ice is low, it’s low next to places with warm sea surface temperatures,” Schneider said.

Losing sea ice around Antarctica can have serious consequences. Without sea ice as a barrier, warmer ocean water starts to lap against ice on land. Where ice stretches over the sea, forming ice shelves, warm water can erode it from below, out of sight of most scientific instruments. This is called basal melting, and it appears to be especially intense in western Antarctica around the Thwaites and Pine Island glaciers. The ice front around the Pine Island Glacier held for 60 years, but suddenly retreated 18 miles between 2015 and 2020. The Thwaites Glacier is also rapidly melting. On its own, it could raise global sea levels by two feet if it were to melt entirely. Further warming in the ocean would accelerate these trends.

Climate Reanalyzer

Why is this heat building up in the air and water right now? In part, for some of the same reasons the Northern Hemisphere is getting so toasty.

The Pacific Ocean is in its warm phase, known as El Niño, and this year it seems to be especially strong. El Niño years are generally associated with higher temperatures in much of the world, including Antarctica. That tends to disrupt the ordinarily circular pattern of high altitude air currents known as the jet streams. “El Niño is always associated with a weaker polar vortex and kind of a wavier jet stream,” Schneider said. Those undulations in the jet stream allow warmer air from higher latitudes to drift over the southern continent and heat it up.

But while El Niño is currently causing warming near the South Pole, climate trends on the continent can be mercurial: For decades, sea ice around Antarctica was actually increasing. Between 1979 and 2014, sea ice increased by roughly 1 percent per decade, according to NASA. “That was unexpected by most people,” Claire Parkinson, a climate scientist at the NASA Goddard Space Flight Center, said. “There’s still no consensus on why the sea ice was increasing.”

Around 2015, that trend changed, with sea ice seeing more fluctuations and declines around the South Pole, in some years even faster than the Arctic region. Scientists aren’t sure why. “The Antarctic case is definitely a puzzle to try to sort out,” Parkinson said.

With so little understanding of why sea ice around Antarctica expanded and then contracted, it’s not clear what the future holds. “I don’t really want to make a prediction for whether these sea ice anomalies are the new normal, or whether it’s going to bounce back,” Schneider said. “The jury is still kind of out on that.”

That uncertainty is adding urgency to research in the Antarctic in order to fill in the blanks. “Even today, we’re fairly undersampled,” Bassis said. “There’s lots of places where you could go out and make a measurement and you’d be the first person to make a measurement there.”

But while scientists sort out the year-to-year shifts in heat and ice, the overall trend still points toward a hotter world and all its ensuing effects. “I can tell you, with really high confidence, that globally, sea levels are going to continue to rise,” Bassis said.