Antarctica appeared to be the only region of the planet that had not received the message about climate change for a considerable amount of time. The floating sea ice surrounding the southern continent continued to grow, obstinately, almost defiantly, while the Arctic was losing ice at an alarming rate. It was once referred to by researchers as the planet’s heartbeat, a term that now seems almost nostalgic. Then 2016 arrived. The ice did not simply retreat. It fell apart.
Scientists are quietly uneasy about what has transpired since. Sea ice extent had dropped so much below the long-term average by the winter of 2023 that statisticians estimated the likelihood of it happening by chance was about one in three and a half million. That wobble is not insignificant. That is a violation of the system. And no one could adequately explain it until recently.
It turns out that the solution was there all along. A complex combination of salinity, wind, and ocean churn is suggested by a recent study headed by Stanford polar oceanographer Earle Wilson. A fleet of Argo floats—torpedo-shaped devices about the size of a person that drift through the Southern Ocean, sinking thousands of feet before bobbing back up to beam data to satellites—performed the grunt work. It may sound dull, but the idea is that they float passively. They have discreetly documented what the ocean is truly doing under its frozen surface year after year.
This is where things start to get interesting. When you dive into most oceans, the surface is warmer than the bottom. It’s reversed around Antarctica. While warmer, saltier water lurks beneath the surface, the bitterly cold air chills it. That arrangement lasted for decades. Sea ice could easily form, the salty warmth remained trapped below, and fresh precipitation kept the top layer light and buoyant. In a way, it served as insulation. The sea was concealing its own heat from itself.
The winds then shifted. They started functioning like a slow pump, pulling that deep warm water upward year after year, strengthened first by the ozone hole and then by greenhouse warming. Storms were able to complete the task by 2015 because the barrier had sufficiently thinned. “What we witnessed was basically this very violent release of all that pent up heat from below that we linked to the sea ice decline,” Wilson stated. It’s difficult not to read that line twice because it’s so striking. In a few seasons, decades of patient accumulation were undone.
Researchers are now concerned that the system appears to be self-sustaining. Warm water melts ice and carries salt with it as it rises. Because saltier surface water is denser and easier to mix with subsurface water, it generates more heat and melts more ice. It’s a feedback loop, and in the field of climate science, feedback loops are rarely positive. They usually don’t stop.
This has a deeper significance that is worth considering. Policymakers rely on climate models, which did not anticipate this on this timeline. The cautious giant of the climate system, Antarctica, was meant to undergo gradual change. The fact that it hasn’t implies that there may be gaps in our understanding of how the earth reacts to warming. Perhaps significant ones.
The stakes are high. If all of the frozen water in the Antarctic ice sheet disappeared, the world’s sea levels would rise by 190 feet. No one is claiming that will happen soon. However, sea ice protects the ecosystems that rely on it by reflecting sunlight, buffering currents, and acting as a sort of shield. It is home to nearly all emperor penguins, which were formally designated as endangered earlier this year. People are more likely to remember that particular detail than statistics.
As I watch this happen, I get the impression that something has changed that won’t be changing back anytime soon. The robots will continue to dive. The information will continue to flow in. Another question is whether the models will be able to catch up in time.
