Images: NASA Earth Observatory, gif by Rosamund Pearce for Carbon Brief
Click to view the break up of Larsen B
Of the 4 Larsen ice shelves, Shelf A became the first ice shelf to collapse in Antarctica in 1995. Shelf B collapsed in 2002. The next southern shelf C, is on the verge of collapse and even further south only Shelf D will remain for the foreseeable future. This process has taken 20 years of warming to get us to this point. Shelf C is about the area of Scotland, "it is five times larger than the Larsen B (itself five times as large as the Larsen A), “so when Larsen C goes, it’s going to be a really big event,” Paul Holland, a researcher with the British Antarctic Survey, said."
Climate Central reports.
The loss of the Larsen A and B ice shelves caused the glaciers behind them to speed their flow to the sea, contributing to the rise of global sea levels that are already threatening the the more than 1 billion people that live along coastlines. Since the beginning of the 20th century, global sea levels have risen by 8 inches, making storm surges during events like Hurricane Sandy higher and more destructive than they once were and causing more regular minor floods in coastal areas.
snip
But on the Antarctic Peninsula — the arm that stretches northward from the continent toward South America — rising air temperatures are impacting the ice. The region is a global hotspot for warming, with temperatures that have risen by about 5°F in the past 50 years, while the globe as a whole has warmed by about 1.3°F.
A study published last year pointed the finger at this warming as the reason for the Larsen B collapse, arguing that the elevated temperatures caused excessive surface melt that led to significant cracks in the ice.
When it comes to the Larsen C shelf, both warming air and melting ice are potential culprits. The surface of the ice shelf has been getting lower and lower in recent decades, but it was unclear what the source of that lowering was. It could be that the layer of compacted snow at the surface, called firn, was melting and compacting further still, or it could be that ice from the bottom of the shelf was melting, causing the height of the glacier to adjust. Or it could be some combination of the two.
The
Carbon Brief explains the new study's finding on the two pronged attack to Larsen C.
The Antarctic Peninsula is one of the fastest warming regions on Earth. Temperatures have risen by 2.5C in the past 50 years, the researchers say.
A separate study last year found that warming air was the principal cause of the Larsen-B collapse. When warm air melts the top of an ice shelf, pools of water form on the surface. The water seeps into cracks in the ice, eroding and widening them until the ice shelf splits and pieces break off. This is how icebergs are formed, in a process called 'calving'. Larsen-B collapsed because of rapid and widespread calving, the researchers found.
Ice shelves can also melt from underneath as the ocean warms. As the ice thins, it loses support from the sea bed as it retreats. This can make it unstable and vulnerable to collapse.
Previously, scientists weren't sure whether the Larsen-C ice sheet was melting from the top down or the bottom up. In another video clip from BAS, Prof David Vaughan, who wasn't directly involved in the study, says the research shows it's actually both:
"All of the indications are that Larsen-C is thinning, and this current research tells us it's thinning from above and from below - a two-pronged attack."
Ice Shelf Stability
There are different factors that affect the stability of the ice shelf, today's paper says. Some would would trigger a collapse over many decades, but others could threaten it in a few years.
For example, a separate study earlier this year found a large crack in the Larsen-C ice shelf grew rapidly during 2014 - at one point extending 20 km in just eight months. This rift could cause a large section of ice to break off, generating "the largest calving event since the 1980s", presenting a significant risk to Larsen-C's stability, the study says.
While scientists might not be able to pin down exactly when the collapse of Larsen-C might be set in motion, today's paper suggests it could well happen without much warming.
We have known that many projections of climate change have been conservative. This is another instance of conservative projections being incorrect. The earths polar regions are warming much more than the rest of the planet. Our coastal populations are threatened even sooner then expected with rising sea levels.
The new study was published today in The Cryosphere.