If you ever watched the hugely popular "Game of Thrones," the HBO drama television series that ran for eight seasons, you probably saw the colossal wall of ice that defended the Seven Kingdoms from all sorts of horrible-wicked invaders from the north. The ice wall in the drama was 700-feet tall.
Now picture Greenland's Jakobshavn glacier, the island's biggest, is over a half-mile thick or more than 3 times taller than the Game of Thrones ice wall. It meets the ocean in Disko Bay, about 2,500 feet of its face is in direct contact with the sea all the way down to bedrock. In other words, 10 million of square feet of it exposed to the ocean.
A bit like the Ice Dragon that burned down the Game of Thrones ice wall with his blue-flamed dragonfire, it was discovered that only small deviations in seawater temperature in contact with the massive glacier can have a profound impact on its growth or decline.
It is not just the air temperatures that control the amount of Greenland ice sheet melt; it is also the temperature of the oceans that surround it. Here is why:
To better understand this process, Jet Propulsion Laboratory (JPL) scientist Josh Willis and the NASA Oceans Melting Greenland (OMG) team have flown out of Greenland's airfields for years. They have deployed numerous bathythermograph (BT) buoys from a recently refurbished Douglas DC-3 cargo plane, which served in the Normandy Invasion in 1944, around Greenland's glaciers.
Throughout the world's oceans, you usually have a negative thermocline. In other words, as you fall deeper and deeper into the sea, the colder the water becomes until you reach a region referred to as cold deep-water thousands of feet down where the water becomes isothermal, with no temperature change all the way to the ocean's floor.
However, in the Arctic and Antarctic regions, the reverse is true; as you descend, the water’s temperature remains the same or even warms up. It is where the ocean is upside down.
OMG team member Ian Fenty noted, "It's rare anywhere on the planet to see 700 meters (2,300 feet) of no temperature variation."
Last year (2019), Greenland experienced record warm temperatures with a few locations reaching over 70 degrees Fahrenheit during the last week of July into the first week of August.
On average, the Greenland ice sheet is now losing about 281 billion tons of ice per year, but in 2019 a record for ice loss at 532 billion tons was reported.
Despite record ice loss in 2019, NASA's OMG project revealed Greenland's Jakobshavn Glacier grew due to the inflow of colder than normal seawater from the North Atlantic Ocean into different areas of the Arctic Ocean that surround Greenland, like Disko Bay.
Since 2017 the seawater temperature in front of Jakobshavn glacier has averaged 1.5 degrees Celsius or 34.7 degrees Fahrenheit. These colder seawater temperatures resulted in the growth of the glacier.
This year the OMG crew discovered that the ocean warmed in front Jakobshavn Glacier to 2.6 C or 36.7 F, which they expect will cause it to shrink a lot between now and summer of 2021. Two degrees of temperature change may not seem a lot, but water is approximately 780 times denser than air, which significantly increases it heat capacity and thermal transfer properties.
Dr. Willis noted that it was a near miracle that they could conduct this year's mission with the COVID-19 pandemic. You see, Greenland has very few cases of the virus, and understandably they want to keep it that way. They had to get permission from six different countries, and the crew was tested five different times for COVID-19 over the course of their mission.
Dr. Willis told me. "In the long run, this Atlantic Water will control just how fast the ice disappears from Greenland."
So far, the loss of ice has resulted in nearly a half an inch of sea-level increase throughout the world. If all the ice were to melt from Greenland, it would produce a 25-foot rise in sea level. Dr. Willis told me that about 40 percent of the recent sea-level increase is due to thermal expansion of the ocean, 30 percent from land glaciers, and 30 percent from the melting of the ice sheets in Greenland and Antarctica.
In the future, the rate of sea-level rise will increase, but the main contributor will be the melting of the ice sheets. Tragically, most of the land glaciers will be gone. In fact, by 2100, most climate scientists are expecting about a 47-inch increase in sea level.
John Lindsey is Pacific Gas and Electric Co.’s Diablo Canyon Power Plant marine meteorologist and a media relations representative. Email him at firstname.lastname@example.org or follow him on Twitter @PGE_John.
Get local news delivered to your inbox!
Subscribe to our Daily Headlines newsletter.