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By Douglas McCauley and Paul DeSalles
(The views expressed are those of the authors, not necessarily Mongabay.)
1. U.S. Drops Out of Paris
In our 2015 ocean top 10 list, we celebrated the adoption of the Paris agreement as a monumental achievement for slowing the warming, acidification and deoxygenation of our global oceans. In 2017, remaining nations like Afghanistan, Nicaragua and Syria ratified the agreement, bringing the total number of ratifying nations to 171. But in a radical about-face of global leadership on climate action, the Trump administration officially declared that the U.S. would withdraw from the Paris agreement, citing unfair impacts on the American economy.
EcoWatch Daily Newsletter
By Ilissa Ocko and Mason Fried
Scientists watched with alarm this week as the fourth-largest ice shelf in Antarctica rapidly broke apart, causing an enormous, Delaware-size iceberg to float into the Southern Ocean.
The iceberg, which will likely be dubbed A68, weighs more than a trillion tonnes, has a volume twice that of Lake Erie, and is about 5,800 square kilometers in size—roughly the size of Delaware.
"The Larsen C Ice shelf in Antarctica is primed to shed an area of more than 5000 square kilometers [approx. 3,100 square miles] following further substantial rift growth," wrote the Project MIDAS team, which has been studying the ice shelf.
"After a few months of steady, incremental advance since the last event, the rift grew suddenly by a further 18 kilometers [about 11 miles] during the second half of December 2016."
During the last Antarctic winter, the rift averaged about three miles per month of growth. In December, NASA released a set of images that found the crack measured 70 miles in length, 300 feet wide and one-third of a mile deep.
The sudden acceleration of the split in the ice has scientists convinced that a massive calving event is imminent.
"If it doesn't go in the next few months, I'll be amazed," Professor Adrian Luckman, project leader from Swansea University, told BBC News.
By itself, the iceberg that is set to break off won't lead to a rise in sea levels, as the ice shelf already floats on the ocean. However, the Larsen ice shelf acts as a buttress against continental glaciers that could then be free to slide into the sea. BBC reports that if all the ice that Larsen C holds back were released into the ocean, global waters would rise by 10 cm, or four inches.
Globally, sea levels have risen about eight inches since 1901. Its effects can be seen in increased flooding in South Florida, coastal erosion in Louisiana, intrusion of seawater into ground aquifers and stronger storm surges such as those seen in Superstorm Sandy.
Long-term satellite observations show that Antarctic glaciers are rapidly retreating. A separate rift in the East Antarctic is forcing a British research station to relocate.
The Larsen C is the latest section of the huge ice shelf to break off. Larsen A collapsed in 1995. In 2002, Larsen B began to break apart. Within six weeks, a 1,235 square mile chunk of ice slipped away.
When the Larsen C ice shelf breaks off, it "will fundamentally change the landscape of the Antarctic Peninsula," said the U.K.-based Project MIDAS team.
An 80-mile long crack in the Larsen C ice shelf threatens to dislodge a chunk of ice measuring about 2,300 square miles, nearly the size of Delaware and twice the size of the massive Larsen B ice shelf collapse in 2002.
As the long Southern Hemisphere polar night is ending, satellites have been able to see that the rift has grown nearly 14 miles, or about three miles per month, since it was last observed in March 2016. The fracture in the ice has also widened from 200 meters (656 feet) to about 350 meters, or 1,148 feet. According to Project MIDAS, a UK-based Antarctic research project, "As this rift continues to extend, it will eventually cause a large section of the ice shelf to break away as an iceberg."
Researchers who have reviewed satellite imagery dating back to 1963 have determined that destabilization of the Larsen B ice shelf was already underway at that time, and began accelerating in more recent decades. Prior to that, it had been stable for 12,000 years. Between January and April of 2002, the ice shelf began to break apart, eventually losing a 1,235 square mile area into the sea. At that time, it was the largest collapse ever seen.
Antarctic ice shelves, which ride atop ocean waters, ring the continent and hold back land-based glaciers. The most vulnerable regions are in West Antarctica and the Antarctic Peninsula. Ice shelves in this region protect a very large portion of glacial ice. The Earth's crust jumped upward following the collapse of Larsen B. Sensitive GPS instrumentation around the ice shelf show that tectonic uplift is now 1.8 centimeters per year as the disappearance of glaciers allows the Earth below to rebound.
However, some of the ice in the shelves is considered "passive" by scientists, in that it doesn't play any role in buttressing glaciers. Some scientists think this may be the case with the Larsen C ice shelf.
The most recent event was the disintegration of the Wilkins Ice Shelf in 2009, the tenth major ice shelf collapse in modern times. Scientists cannot predict the timing of the Larsen C collapse, but say it could happen in the next two to three years. A study published in 2015 showed that Larsen C is rapidly thinning, having lost four meters, or 13 feet, between 1998 and 2012. As the ice thins, it is susceptible to melting from underneath.
Of itself, the loss of this portion of the ice shelf will not raise sea levels as it is already floating on the water. However, as these ice shelves disintegrate, the land-locked glaciers they hold back may begin sliding into the sea. If all of the ice the Larsen C ice shelf holds back slides into the ocean, it will raise sea levels globally by four inches.
Warmer air temperatures were blamed for the collapse of Larsen B. By melting the top layer, pools of meltwater form and seep through crevasses causing fracturing of the ice. This process is now being seen on the Langhovde Glacier in East Antarctica, on the opposite side of the continent from the Larsen ice shelf.
Temperatures at the Antarctic Peninsula, where the Larsen ice shelf is found, have risen by 2.5 degrees Celsius in the past 50 years. On March 24, 2015, a record high of 63.5 degrees Fahrenheit was recorded on the peninsula at Esperanza Base.