Like a trio of canaries in a coal mine warbling at the top of their lungs, three recent studies warn of various ways that global warming is drastically changing the planet. Each study involves the cryosphere, or those regions on the planet where water freezes into ice or snow. Both the Arctic and the Antarctic are melting — and scientists are recording the consequences.
First is a study by researchers from the University of Colorado Boulder and published in the journal Nature Reviews Earth & Environment. After creating models based on past data chronicling sea ice area shrinkage in the Arctic Ocean, the scientists determined that we will soon enter an unprecedented future... one where during the summer there is no sea ice at all. Notably, this will happen regardless of whether humanity meets the emissions targets set during the Paris climate accord.
"The earliest ice-free conditions (the first single occurrence of an ice-free Arctic) could occur in 2020–2030s under all emission trajectories and are likely to occur by 2050," the authors write. This does not mean that the ocean will have literally zero ice in it, but rather that it meets the scientific definition of being "ice-free": When the entire Arctic Ocean has less than 1 square kilometer (or 0.386 square miles) of ice.
At that point, the quantity of ice will be less than 20% of the Arctic seasonal minimum from the 1980s. Because this is unprecedented in recorded history, scientists whose disciplines involve Arctic work will have to encounter a very different environment. There is a nuance to how the region's wildlife will be impacted, and how weather overall will change, based on whether there is occasional daily ice-free conditions, frequent monthly ice-free conditions or even ice-free conditions that last for as long as nine months. Experts will need to understand each different scenario "to assess the true impact of what the transition of the Arctic sea ice cover into its new seasonal sea ice regime means in a warming world."
That last scenario — one in which humanity blows past its emissions goals and the region is ice-free for stretches of up to nine months — would be disastrous.
“This would transform the Arctic into a completely different environment, from a white summer Arctic to a blue Arctic," Alexandra Jahn, associate professor of atmospheric and oceanic sciences and fellow at CU Boulder’s Institute of Arctic and Alpine Research and co-author of the paper, said in a statement. "So even if ice-free conditions are unavoidable, we still need to keep our emissions as low as possible to avoid prolonged ice-free conditions.”
Like the authors of the Nature Reviews Earth & Environment paper, the scientists behind a recent study for the journal Proceedings of the National Academy of Science (PNAS) used decades of data about sea ice to project future conditions. This time, though, the authors focused on the Antarctic, and their goal is to anticipate the proliferation of polynyas, or pockets of open water that can exist within sea ice. Led by researchers from the University of Otago, the authors were surprised to discover a dramatic increase in the area of polynyas around Antarctica. At this rate, coastal animals and plants may one day move onto the continent itself.
This is not entirely due to climate change. Some of it appears to be caused by cyclical factors, and could be fueled by phenomena such as the interactions between the Amundsen Sea Low and Southern Annular Mode. Yet the planet's ongoing warming — which is primarily caused by humans burning fossil fuels — is without question a factor too.
“Recent record low Antarctic sea ice coverage has been linked with ocean warming,” co-author Dr Ariaan Purich, a scientist at Monash University in Australia who studies ocean-atmosphere interactions, said in a press statement. “In coastal environments, large-scale atmospheric variability and trends can interact with changing ocean conditions to shape the extent of sea ice. These findings give us exciting insights that will help us predict coastal sea ice coverage in the future.”
In the study itself, the authors acknowledge that the "specific drivers remain unknown," yet emphasize that because climate change could put humanity in a "new age of Antarctic sea ice," advanced knowledge of both the cycle and the consequences of human activity "will, in turn, lead to more accurate predictions of environmental change, and its implications for Antarctic ecosystems."
Finally, there is another study from PNAS, this one about how Arctic sea life has responded to the loss of 1 million square kilometers of sea ice over the past 25 years. Specifically, the authors studied the seafloor for so-called "benthic primary producers (BPPs)," or the microalgae, macroalgae and seagrasses that are essential to Arctic ecosystems but were nonetheless previously poorly studied. "Primary production" is a term for the process through which some life forms create energy by absorbing organic compounds from the atmosphere, such as through sunlight. Although the scientists thought that the seafloor-dwelling primary producers might flourish in the warmer ocean waters caused by climate change, this did not prove to be the case.
"Microalgal benthic primary production has increased in only a few shelf regions despite substantial sea ice loss over the past 20 [years] as higher solar irradiance in the ice-free ocean is counterbalanced by reduced water transparency," the authors write. "This suggests complex impacts of climate change on Arctic light availability and marine primary production."
The reason they were surprised is that, although primary producers on the seafloor might theoretically benefit from climate change causing more heat, that is more than offset by how sediments, dissolved substances in the water and phytoplankton absorb all of that sunlight first. They can do this because the water is more transparent than before.
“Our study suggests that the impacts of climate change on sunlight availability and primary production in the Arctic Ocean are complex," co-author Dr. Karl Attard, a marine scientist and Assistant Professor at the Department of Biology in the University of Southern Denmark, said in a press statement. "Additionally, as the Arctic Ocean continues to warm, we may witness more species migrating from lower latitudes, potentially leading to a more productive marine environment than what exists today — at the cost of losing what is special for the Arctic."
