Antarctica may have crossed a tipping point that leads to rising seas

Recent studies have raised alarm bells among scientists, suggesting that Antarctica may have crossed a critical climate tipping point. Evidence indicates a significant decline in sea ice since 2016, closely linked to human-induced ocean warming.

Historically, Antarctic sea ice levels showed remarkable stability despite a global temperature rise. This trend abruptly changed in 2016 when a notable decrease in sea ice extent began.

February 2023 marked a record low for Antarctic sea ice, representing the third consecutive summer of unprecedented low levels within a mere seven years. Likewise, September 2023 recorded the lowest maximum extent for Antarctic sea ice on record.

While climate models have long warned of accelerating sea ice loss in Antarctica, the recent velocity and scale of this decline have taken the scientific community by surprise. Researchers convened at the Royal Society in London recently to deliberate whether these changes signify a climate tipping point.

According to Marilyn Raphael from UCLA, the rapid shift cannot be attributed to natural climate variability. The satellite record for sea ice began in 1979; Raphael and her colleagues utilized proxy data from weather stations across Antarctica to extend historical records back to the early 1900s.

They found that based solely on historical data, the likelihood of experiencing the sea ice minimum recorded in 2023 was less than 0.1%. “We are truly witnessing extreme behavior regarding sea ice,” Raphael expressed at the Royal Society meeting.

The sharp decline in ice formation exhibits characteristics of a climate tipping point, as noted by Alexander Haumann from the Alfred Wegener Institute in Germany. He stated that these rapid changes are continent-wide and will likely have profound impacts on Antarctica’s broader climate and ecological systems.

“What we are currently observing is a collective response from all Antarctic sea ice,” Haumann remarked in an interview with New Scientist. “These transformations seem to have long-lasting effects within the ice system.”

Haumann attributes this phenomenon to a “superimposed change” affecting the sea ice. New insights suggest that warming ocean waters are a critical driver behind the rapid decline. The world’s oceans have absorbed about 90% of the excess heat generated by human activities.

Normally, warmer deep ocean waters remain isolated from surface waters by a layer of lighter freshwater. However, emerging findings led by Haumann indicate that shifts in wind patterns and salinity in the Southern Ocean have weakened this boundary layer since 2015, enabling warm deep water to rise to the surface and expedite ice loss. This deep water has been warming due to climate change, confirming previous research.

While natural climate variability may have instigated the changes in ocean salinity and winds, Haumann cautions that this has released the effects of human-induced warming trapped in deeper water. This implies that the repercussions of warmer ocean waters are beginning to surface in Antarctica, resulting in a decline in new sea ice formation.

The recent shifts in ocean circulation may only be reversed by reducing the upwelling of warmer water or by significant changes to the salinity of the Southern Ocean, such as a massive influx of freshwater from a melting glacier. However, as Haumann notes, the future response of the system remains highly unpredictable.

The potential consequences of this recent development are alarming. The sea ice surrounding Antarctica plays a crucial role in stabilizing glaciers and land ice sheets. A decrease in sea ice formation could accelerate their melting rates, posing a threat of extreme global sea level rise. Notably, the Antarctic ice sheet harbors enough water to raise global sea levels by an estimated 58 meters.

The retreat of Antarctic sea ice will also impact the Earth’s albedo, as darker ocean waters absorb more solar heat compared to reflective ice. This transition could further exacerbate global warming.

Additionally, hundreds of gigatonnes of carbon stored in deep Southern Ocean waters could be released into the atmosphere due to increased upwelling of deeper water, as suggested by ongoing research.

Scientists are just beginning to grasp how these complex feedback mechanisms will play out in Antarctica amidst a backdrop of decades spent wrestling with low-resolution models and inaccurate data.