After last week’s Arctic-fueled cold snap — dubbed the ‘Polar Vortex’ — brought freezing temperatures and claims of climate change denial to the attention of the general public, the situation has now returned to normal. Or the new normal at least — in which climate change happens out-of-sight and out-of-mind for many Americans.
One of the latest indicators that climate change is progressing whether we’re looking or not comes from a study in the journal Nature Climate Change finding that one of the largest glaciers in Antarctica has started melting irreversibly.
An international team of researchers found that Antarctica’s Pine Island Glacier, the single largest Antarctic contributor to sea-level rise, could add as much as one centimeter to ocean levels within the next 20 years.
The glacier “has started a phase of self-sustained retreat and will irreversibly continue its decline,” Gael Durand, a glaciologist with France’s Grenoble Alps University, told Australian Broadcasting Corporation.
The team of researchers used state-of-the-art ice-flow models and field observations to help determine how the glacier’s ice flows will change in coming years.
“At the Pine Island Glacier we have seen that not only is more ice flowing from the glacier into the ocean, but it’s also flowing faster across the grounding line — the boundary between the grounded ice and the floating ice,” Dr. G. Hilmar Gudmundsson, a researcher on the project, told Planet Earth Magazine.
The glaciologists found that that glacier’s grounding line, which has already receded up to 10 kilometers this century, is “probably engaged in an unstable 40-kilometer retreat.”
Pine Island Glacier is one of the main avenues for ice to flow from Antarctica into the ocean. As the tip of the glacier melts and thins, the glacier is discharging more ice into the sea. The glacier has been losing about 20 billion tonnes of ice a year for the last two decades, but scientists see this rising to 100 billion tonnes a year in the coming decades.
Pine Island Glacier accounts for about one-fourth of the total ice melt from the West Antarctic Ice Sheet. If the entire West Antarctic Ice Sheet retreated it could cause sea level to rise by more than 10 feet. The entire Antarctic Ice Sheet, covering an area bigger than the continental U.S., contains nine-tenths of the ice on Earth and could raise sea level by over 200 feet if it melted.
Understanding how climate change causes glaciers to melt and thus sea level to rise is an important part of future climate modeling and planning.
According to the latest research, Antarctic ice melt has caused global sea level to rise by about 0.02 centimeters a year for the last 20 years. Last year’s Intergovernmental Panel on Climate Change report stated that there was “high confidence that ice shelves around the Antarctic peninsula continue a long-term trend of retreat and partial collapse that began decades ago.”
Another recent study found that attributing the eroding of the West Antarctic Ice Sheet to simple and steady ocean warming is too straightforward, and that depletion of Antarctic glaciers is more susceptible to climate variability over a wide range of time scales.
“These new results show that how much melt the Antarctic ice sheet experiences can be highly dependent on climatic conditions occurring elsewhere on the planet,” study co-author Eric Steig, a University of Washington professor of earth and space sciences, said.
Researchers found that melting ice flows from glaciers in the West Antarctic Ice Sheet decreased by half between 2010 and 2012. They believe this unexpected phenomenon can be attributed to ocean cooling caused by winds associated with a La Niña event that led to less warm water flowing into the area. If these conditions continued, the edge of the Pine Island Glacier could even start to rebuild — however this is unlikely.
“2012 was probably just a rare event,” Steig said. “I expect that a return visit to Pine Island area would find conditions much more similar to those observed in earlier years.”