The US decision is part of what has been widely described as an assault on climate science by the Trump administration. It also affects other work by NASA and the National Oceanic and Atmospheric Association, including hurricane forecasting, as reported by The Guardian US. This masthead sent questions to the US embassy in Australia and the Pentagon, but did not receive a response by deadline.
One important dataset under threat is the Sea Ice Index, which has continuous readings back to the late 1970s. It shows that until about 2015, sea ice was around average, or even a bit above average, but since 2016 it has been consistently low.
Doddridge said the satellites were past their mission life but remained operational, suggesting the data would still exist but not be shared for scientific work, forcing scientists to use sources with less reliability and continuity such as Japanese or Chinese satellites.
“We won’t lose complete access to sea ice data,” Doddridge said. “What we will lose is a long-term record of well-calibrated, interoperable satellite sensors. What that means is that we won’t be able to compare future extremes with past extremes anywhere near as accurately.”
The impacts of extremely low sea ice in Antarctica
The PNAS Nexus paper canvasses a wide range of impacts from extremely low sea ice, from ecological harm to feedback loops for global warming.
Emperor penguins needed landfast sea ice for breeding platforms, Doddridge said, while Adelie penguins relied on sea ice to stay dry while they underwent a “catastrophic moult”, in which they replace all their feathers over a few weeks and temporarily lose their waterproofing.
Crabeater seals give birth to their pups on large ice floes and need to stay with them for the two to three weeks between birth and weaning, but are vulnerable to predators such as leopard seals if the ice floes become smaller or harder to find.
Krill in blue water in Antarctica. Krill larvae rely on sea ice.Credit: Brett Wilks / AAPP
The paper also raises the spectre that low sea ice could affect the population of Antarctic krill, small crustaceans that are a main food source for a number of whale species, and which need sea ice in the larval stage.
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Perhaps the biggest impact of low sea ice is the feedback effect it could have on the destruction of the ice shelf – the part of the ice sheet of compacted snow that sits on the ocean rather than over rock – through iceberg formation or melting, and the corresponding effect on sea level rises.
Dr Sue Cook, a glaciologist and co-author on the PNAS Nexus paper, said sea ice suppressed ocean swells and waves close to the ice shelf. If the ice shelf was directly exposed to swell, it would start to bend and crack and might disintegrate into icebergs that then disperse out into the open ocean, Cook said.
The ice sheet is more exposed to waves without sea ice.Credit: Pete Harmsen / AAPP
“In the 15-year record that we looked at, the years with the least summer sea ice produced more than twice as many icebergs as the years with the most summer sea ice,” Cook said.
“This link between iceberg production and sea ice presence isn’t something that we include in any of our ice sheet models at the moment, and that means that we might be underpredicting how quickly the Antarctic margin will retreat as sea ice dwindles around the continent.”
She added that most models were based on 15 to 20 years of data, which included long periods of good sea ice coverage.
“If we shift to this state where summer sea ice is very low, but we continue using models based on the previous period, then we will definitely underestimate how quickly Antarctica will contribute to sea level rise,” she said.
Aerial view of a crack in the pack ice.Credit: Kim Newbery / AAPP
Dr Will Hobbs, a sea ice scientist with AAPP and co-author of the paper, said one of the most important roles of sea ice was the albedo effect, in which it essentially acts as a sunshade in summer. This works because snow-covered ice reflects about 90 per cent of the sunlight back into space, whereas the darker water of the open ocean absorbs 90 per cent of the sunlight, and warms accordingly.
Hobbs said that historically in the Southern Ocean, the system always resets in the midwinter, but the researchers found that in a year of extremely low ice, such as 2016, it would affect the next summer and take about three years to fully recover.
Hobbs said statistical analysis using reconstructions of the last century suggested there was a 0.1 per cent chance that the low sea ice trend was part of natural variability.
He said one reason why Antarctica had not already suffered sea ice loss on the scale of the Arctic was because it was connected to open ocean and any warmth at the surface was being transported northward by ocean currents to lower latitudes. The temperature of the waters north of Antarctica had been way above average for about five years now, far predating the current marine heatwave around Australia.
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