Greenland Ice Sheet melting at unprecedented rate in past 350 years or more

The magnitude of recent Greenland Ice Sheet melting is "exceptional" compared to the historical records for the past 350 years, according to a new study by a team of researchers from the U.S. and the Netherlands.

Background: When it comes to Greenland and sea-level rise, the basics are well known — air temperatures are rising, causing ice to melt from above. The water percolates down through the ice, and eventually flows into the ocean, where it adds to sea level. At the same time, glaciers are accelerating their flow into the sea as warming ocean temperatures eat away at them from below.

Yes, but: The big question is — to what extent is the level of summer surface melting unusual?

Why it matters: Refining the dynamics of sea-level rise would help scientists to predict how much damage to expect in coastal regions of the world. It would also help them determine what to anticipate from a slowdown in a crucial ocean current that draws heat north from the equator, changing ecosystems and weather patterns.

What they did: The researchers collected and analyzed ice cores from Central West Greenland and a coastal location on the Nuussuaq Peninsula in 2015.

• They were able to detect when the ice melted and refroze, and how often and significantly it did so through time.
• These observations provide a critical window into how ice melt varies over time, as well as the intensity of the melt and how much water runs off the surface, which are the main ways the ice sheet is losing mass.
• The study co-authors put together a 330-year record of melt, percolation and refreezing in the west-central region of the island, as well as a 364-year record of the same variables at the more coastal location.

What they found: In recent decades, there was a clear departure toward more melting, water percolation through the ice, and refreezing each winter.

• The study found a 250%–575% increase in melt intensity in the last 20 years, compared to the pre-industrial era.

• And, the most recent decade had a more sustained and significant magnitude of melt than any other 10-year period in the ice core records.
• The core records matched with computer model simulations and satellite observations of the ice sheet as a whole.

The study concludes that as ice melts, the surface darkens, absorbing more heat and melting more ice. While this process has long been known, the new study underscores its significance, since it means the surface of the ice sheet can be extremely sensitive to seemingly small upticks in summer air temperatures.

"As a result, Greenland is more sensitive to temperature change today than just a few decades ago. Warming matters more than ever."

The bottom line: "This is a climate record you can easily put alongside a history book — clearly seeing [the] humans fingerprint on the Greenland Ice Sheet," Robin Bell, a research professor at the Lamont-Doherty Earth Observatory at Columbia University, tells Axios. Bell was not involved in the study.