By Paul Voosen , Science.  Excerpt: For nearly 4 decades, researchers have tracked one of the most prominent harbingers of global warming—dwindling Arctic sea ice—with data from aging weather satellites run by the U.S. military. But this continuous record is now at risk, after the Department of Defense (DOD) quietly told climate scientists it would be “deprioritizing” access to the data. The move comes as Arctic sea ice approaches a possible new record low. “The [satellites] are up there and functioning,” says Walt Meier, a remote-sensing scientist at the U.S. National Snow and Ice Data Center (NSIDC). “But we’re not getting all the data anymore, at least regularly.” NSIDC and Europe’s Copernicus Climate Change Service compile the two most prominent global records of sea ice, and both groups rely on these data. The only options for similar observations come from either an  aging Japanese satellite , launched in 2012, or a series of Chinese weather satellites, which the country...

By Sophie Hardach, BBC.  Excerpt: A photographer's iconic shot of polar bears in abandoned buildings on a Russian island shines a spotlight on wider changes in their behaviour. ...Smith notes that polar bears are  spending more time on land  due to the climate-change-driven  loss of sea ice . They are also shifting their dens from the ice onto the land, to avoid the risk of denning on the increasingly unstable sea ice,  research in northern Alaska  shows. Without the sea ice, the  bears can't hunt  for their  preferred, ideal diet  of  blubber-rich seals , and may  resort to land-based food , be it prey or rubbish. ...A 2022 research paper warns that food from human sources – especially waste – is an  emerging threat  to polar bears. The supply of such human-provided food including from dumps is growing, according to the paper. As a consequence, some communities in the Arctic have seen startling incursions of dozens o...

By Julienne C. Stroeve et al, Science.  Abstract: Under current nationally determined contributions (NDCs) to mitigate greenhouse gas emissions, global warming is projected to reach 2.7°C above preindustrial levels. In this review, we show that at such a level of warming, the Arctic would be transformed beyond contemporary recognition: Virtually every day of the year would have air temperatures higher than preindustrial extremes, the Arctic Ocean would be essentially ice free for several months in summer, the area of Greenland that reaches melting temperatures for at least a month would roughly quadruple, and the area of permafrost would be roughly half of what it was in preindustrial times. These geophysical changes go along with widespread ecosystem disruptions and infrastructure damage, which, as we show here, could be substantially reduced by increased efforts to limit global warming....  Full article at https://www.science.org/doi/10.1126/science.ads1549 .  See...

By Louise C. Archer et al, Science.  Summary: ...polar bear populations have declined over the past 50 years as the extent of sea ice has decreased. Archer  et al . used data collected from polar bears in the western Hudson Bay Area over nearly all of that time.... Energetic patterns at the individual level successfully predicted larger-scale population dynamics. A single driver, energy limitation, emerged as being responsible for the population decline, confirming that polar bears face food shortages due to the loss of ice. —Sacha Vignieri....  Full article at https://www.science.org/doi/10.1126/science.adp3752 . 

https://www.science.org/doi/10.1126/sciadv.adf3326 By MICHAEL V. WESTBURY et al, Science Advances.  Excerpt: The Arctic is among the most climatically sensitive environments on Earth, and the disappearance of multiyear sea ice in the Arctic Ocean is predicted within decades. As apex predators, polar bears are sentinel species for addressing the impact of environmental variability on Arctic marine ecosystems. ...we investigate how Holocene environmental changes affected polar bears around Greenland. We uncover reductions in effective population size coinciding with increases in annual mean sea surface temperature, reduction in sea ice cover, declines in suitable habitat, and shifts in suitable habitat northward. ...[over the past 11,000 years...Whenever temperatures rise, polar bear populations crash. For example, about 4500 years ago, sea surface temperatures climbed by 0.2°C, sea ice cover shrank by about 3%, and polar bear populations dropped by about 20%. Several thousand ...

https://www.sciencenews.org/article/ice-melting-dipole-arctic-oscillation By arolyn Gramling , Science. Excerpt: From 2007 to 2021, winds over North America and Eurasia were circulating in such a way that  they reduced the influx of warmer Atlantic water into the Arctic , researchers report in the Sept. 1  Science . That helped slow the rate of sea ice loss during that time period —  even as atmospheric warming ramped up  ( SN: 8/11/22 ). But that grace period may come to an end within just a few years. When the winds shift back, enhanced “Atlantification” of the Arctic may speed up sea ice loss, by giving an extra oomph of warming from below. “This phase has lasted about 15 years. We’re about at the end,” says physical oceanographer Igor Polyakov of the University of Alaska Fairbanks. ...From 1979 to 2006, the Arctic Dipole was in a “negative” phase, with winds rotating counterclockwise over North America and clockwise over Eurasia. That brought more Atlantic w...

  https://eos.org/articles/sea-ice-is-going-but-when-will-it-be-gone By  Saima May Sidik , Eos/AGU.  Excerpt: Every September since 1979, the U.S. government has  measured the extent of sea ice  in the Arctic. And the picture is not a pretty one—more than 2 million square kilometers have been lost in that time, leaving about 4.67 million square kilometers of sea ice intact. ...climate models underestimate the melting that’s been observed in recent years, leaving scientists uncertain of whether they can use these models to make predictions. Two new publications have added to this discussion.  The first , published in  Nature Communications , provided evidence that the Arctic will become seasonally sea ice free in the next few decades even under low-emissions scenarios.  The second , published in  Nature Climate Change , proposed that the extent of Arctic sea ice will decline more slowly than previously thought because the effect of wind has no...

https://www.science.org/content/article/dwindling-sea-ice-may-speed-melting-antarctic-glaciers By Paul Voosen, Science.  Excerpt: In February, on an icebreaker off the coast of West Antarctica, Robert Larter, a marine geophysicist with the British Antarctic Survey (BAS), came on deck to a startling sight: open gray water as far as the eye could see. There was no ice at all for the ship to break. The next day, satellite surveys would find sea ice around the continent hitting a record low. Unlike fast-shrinking Arctic sea ice, the sea ice ringing Antarctica seemed more resistant to climate change—until recently. But now a long-term decline may have set in, and it could have unexpected and ominous domino effects, according to several recent studies. Dwindling sea ice could strengthen a whirling current called the Ross Gyre, bringing warm waters closer to land and hastening the  collapse of the West Antarctic ice sheet , which locks up enough water to  raise global sea levels...