Between 1979 and 2016, Earth’s cryosphere – the planet’s frozen water – decreased by around 87,000 square kilometers (33,590 square miles of ice) per year, according to a 2021 study in Earth’s Future. The researchers examined data sets for snow cover, sea ice, and “near-surface frozen soils” to come to this conclusion.
The scientists determined that the cryosphere lost an average of 102,000 square kilometers (39,300 square miles) in the Northern hemisphere in each of those years, and gained around 15,000 square kilometers (5,790 square miles) in the Southern hemisphere annually. This Antarctic increase is largely the result of more sea ice in part of the Ross Sea, which could be related to circulation changes or other factors.
Arctic sea ice: 15 years of lows
Formed when ocean water freezes, Arctic sea ice is important for a variety of reasons. It serves as an insulating barrier to keep heat within the ocean, rather than allowing it to go up into the atmosphere. Thicker and older ice provides more insulation than thinner, recently formed ice. Melting sea ice can change the ocean’s nutrient balance, adversely affecting phytoplankton, which provides sustenance for many species. While sea ice melt isn’t a significant contributor to sea-level rise, since it is formed from water already in the ocean, its loss adversely affects the ecosystem … and in ways going well beyond its widely recognized role in providing needed habitat for animals such as polar bears.
For more than 40 years, researchers have used satellite data to calculate the “sea ice minimum,” measuring sea ice in September, when it is at its lowest for the calendar year. All of the 15 lowest recorded sea ice minimums have occurred during the past 15 years. In 2021, the ice was measured as the 12th lowest minimum recorded.
Researchers measure minimum sea ice after each summer, and in the spring they measure how much ice is present after the winter. In April 2021, they reported that the ice volume was the lowest found since 2010, and they shared that finding in NOAA’s Arctic Report Card. “The amount of older, biologically important multiyear sea ice at the end of summer 2021,” they wrote, “was the second-lowest since records began in 1985.” Less ice on top of the world means more ships can travel further into the Arctic, leading to concerns about everything from wildlife disturbance to pollution, oil spills, national security, and other concerns.
It’s important to underscore that when measuring sea ice, the expanse of ice, the number of square miles covered, is significant, but so too are depth and age of the ice crucial factors. Thicker, older ice is more resilient, and it also provides a better insulating layer. New, thinner ice can fracture and melt more easily, and it also moves more easily with winds and ocean currents.
Scientists have long known that light-colored or white sea ice reflects far more of the sun’s energy than does the dark open ocean. Now, researchers have found in a 2021 study in the Journal of Geophysical Research: Atmospheric conditions that open areas of water close to sea ice – called polynas – may actually lead to more cloud formation. They studied a polyna by Baffin Bay, finding more clouds and moisture over the polyna. These clouds can help trap heat, making it more difficult for the ice to refreeze, and as a result further contributing to warming of the atmosphere.
Diminishing sea ice could also cause more and stronger Arctic cyclones. In the Journal of Geophysical Research: Atmospheres, researchers studied Arctic storms and sea ice from 1979 to 2015. They found that from December to May, when there was less sea ice, more frequent and stronger cyclones overall were recorded.
Part of the ‘Last Ice Area’ – Wandel Sea
The Wandel Sea, north of Greenland, is considered part of the “Last Ice Area” in the Arctic. For ice-associated animals, like polar bears and some seals and walruses, this area is considered a last refuge.
The area is where scientists have expected thick, aged sea ice to remain the longest, but in the summer of 2020, they found record-low levels of sea ice. On August 14, 2020, they recorded about half the level of ice they would normally expect. These researchers published their findings in 2021 in Communications Earth & Environment. Using satellite data, they created models to study what was happening, learning that unusual wind patterns were likely pushing ice away, leaving open areas of water (polynyas) behind. They attributed 80% of the record-low ice level to wind and weather patterns, and the remaining 20% to human-caused climate change.
These patches of open water are not unique to the Wandel Sea. In a 2021 study in Geophysical Research Letters, researchers reported finding a large polyna north of Ellesmere Island, in another section of the “Last Ice Area.” Here, scientists often find ice up to 5 meters (16 feet thick), but in May 2020, they found a Rhode Island-sized hole that lasted for two weeks or so. Extreme winds were largely to blame for this occurrence, according to the scientists.
The 656,000-square-mile (1.7 million square kilometer) Greenland Ice Sheet is one of the world’s two major bodies of ice (along with the Antarctic Ice Sheet). In its 2021 Arctic Report Card, NOAA reported that the Greenland Ice Sheet has been declining in mass since 1998, with declines in all but a few of those years, setting records for ice loss in 2012 and 2019. In 2021, rain attracted widespread mainstream media attention: the first rainfall known to have fallen at the summit of the ice sheet, 10,500 feet in elevation.
Researchers of a study in Proceedings of the National Academy of Sciences, PNAS, found parts of the Greenland Ice Sheet might be veering towards instability and may be on the way to a tipping point. “We reveal early-warning signals for a forthcoming critical transition from ice-core-derived height reconstructions,” the researchers wrote, “and infer that the western Greenland Ice Sheet has been losing stability in response to rising temperatures.” They continued, “Our results suggest substantially enhanced melting in the near future.”
As researchers work to learn about ice in Earth’s far-northern stretches, they strive also to communicate how changes in the cryosphere can affect people and the environment worldwide. While some impacts of climate change are visible, such as large expanses of open water where there usually was sea ice, other changes are virtually invisible to the untrained eye, such as changes in ocean nutrients and phytoplankton. These changes in the cryosphere ripple and affect people and ecosystems far from the ice. Less ice to reflect the sun’s rays contributes to further warming of the world’s atmosphere, and significant melting of the Greenland Ice Sheet would substantially increase global sea-level rise and inundate highly populated low-lying communities around the world.
Also see: What the latest science says about Antarctica and sea-level rise