Bad News from Thwaites Glacier
Area of West Antarctica showing 6 large glaciers, colorized to show velocity.
Even back in 2012, in my book High Tide On Main Street: Rising Sea Level and the Coming Coastal Crisis, I pointed to a few “mega glaciers” as being the key factor for future sea level rise. Each of them could raise global sea level by more than a foot, whenever they slid into the ocean. I named the three big ones: Jakobshavn in Greenland and Pine Island and Thwaites in Antarctica.
Since then I have mentioned them in several blog posts, such as in 2016, The Elephants of Antarctica and Greenland, figuratively meaning that those sources of higher sea level are the proverbial “elephants in the room.” (My 2012 blog post at https://johnenglander.net/wp/sea-level-rise-blog/west-antarctica-warming-3-x-faster-than-average/ had specifics about Thwaites.)
Last Thursday, January 30, 2019, NASA and JPL (Jet Propulsion Laboratory) put out a news release that raised the level of concern. The huge Thwaites Glacier was found to have a cavernous void far below the surface. The story made the mainstream news media, but the significance may not have been clear. The headline was:
“Huge Cavity in Antarctic Glacier Signals Rapid Decay”
As the story stated, this one glacier is roughly the size of the state of Florida. It is slowly sliding off of the Antarctic continent and into the ocean.That one glacier will raise global sea level approximately 2 feet (65 cm) when it fully moves into the sea. Because these giant “rivers of ice” grind along slowly on bedrock, moving down valleys and around the “hills” on the land underneath them, the forward speed is hard to predict. Speed varies greatly but a few miles a year towards the sea, is a good estimate.
The big news in this story last week was about the size of the cavern, where the glacier would normally be in contact with the bedrock of Antarctica. This diagram of its sister glacier, the Pine Island Glacier illustrates the situation. A large cavity means that more seawater can melt the glacier from below. Even though the water is very cold, it contains a lot more heat energy than does air and is able to melt the glacier much faster than from the topside.
Also, as the glacier is melted from below, moving the “grounding line” back, it makes it possible for the glacier to slide over the high spots in the bedrock labeled here as continental shelf. When enough ice is eaten away below, the glacier will be clear to slide into the ocean, raising sea levels globally.
Noteworthy in this story, is that new data collected by satellites and aircraft that can penetrate the miles deep ice with radar and mass detection devices showed that the cavity underneath Thwaites was a thousand feet high (300 meters) and nearly the size of New York City – far larger than previously believed.
The good news is that these glaciers cannot quickly raise sea level, in the way that a tsunami or hurricane can bring a “wall of water” in hours. Even at the fastest possible melt rate, global sea level rise is probably on the order of a foot or two a decade (50 cm). Of course even that rate of global sea level rise would cause havoc and devastation in coastal communities globally. It is because of uncertainty about the rate of melting and collapse of those mega glaciers that we cannot precisely predict the rate of sea level rise.
We are sliding down a slippery slope.The image below is from last week showing a large iceberg calving off the tongue of Thwaites Glacier. Our window of time to adapt to rising sea level is getting shorter and shorter. The new information from Thwaites should sound an alarm bell.
Large iceberg calving off from Thwaites Glacier, Antarctica. New data shows a gigantic cavern underneath raising sea level rise scenarios. (NASA Photo)