In a groundbreaking study, NASA’s Jet Propulsion Laboratory (JPL) in Southern California reveals that the Greenland Ice Sheet has undergone a more substantial loss of ice mass over the last four decades than initially thought. The study, published in Nature on January 17, presents a meticulous analysis of satellite data, encompassing nearly a quarter million data points on glacier positions from 1985 to 2022.
The findings are staggering – approximately one-fifth more ice mass has melted compared to previous estimates. The research highlights a significant retreat in the majority of glaciers across the landmass, accompanied by an accelerated rate of icebergs calving into the ocean. Although this extra ice loss has not directly contributed to rising sea levels, it holds potential implications for future ocean circulation.
The study delves into the retreat patterns along the edges of the entire ice sheet, focusing on 207 glaciers. Astonishingly, 179 of these glaciers experienced significant retreat since 1985, while 27 maintained their positions, and only one displayed marginal advancement.
A notable revelation is that most ice loss occurred beneath sea level, particularly in Greenland’s fjords. These deep coastal valleys, once filled with ancient glacial ice, are now submerged in seawater. Consequently, the ice breaking off contributes minimally to rising sea levels. However, the study suggests that this loss may intensify the flow of ice from higher elevations, ultimately contributing to sea level rise.
“When the ice at the end of a glacier calves and retreats, it’s like pulling the plug out of the fjord, which lets ice drain into the ocean faster.” explains Chad Greene, the lead author of the study and a glacier scientist at JPL.
The study challenges previous assessments that focused on the direct contributions of the Greenland Ice Sheet to global sea level rise. The Ice sheet Mass Balance Inter-comparison Exercise (IMBIE) estimated a loss of 5,390 billion tons (4,890 billion metric tons) between 1992 and 2020, adding about 0.531 inches (13.5 millimeters) to global mean sea level. However, this did not account for ice lost due to the retreat of terminal glaciers along Greenland’s edges.
The new analysis quantifies this overlooked loss, revealing that the ice sheet lost about 1,140 billion tons (1,034 billion metric tons) from 1985 to 2022, 21% more than the IMBIE assessment. While not directly impacting sea levels, this additional ice represents a substantial influx of fresh water into the ocean.
Recent studies suggest that changes in the North Atlantic Ocean’s salinity from melting icebergs could weaken the Atlantic Meridional Overturning Circulation, potentially influencing global weather patterns and ecosystems.
Examining the comprehensive data on glacier positions, the study notes a consistent and alarming trend of ice retreat outpacing growth throughout the 21st century. Greenland’s ice extent remained relatively steady from 1985 to 2000, followed by a marked recession that continues to this day.
The study identifies specific glaciers, such as Zachariae Isstrom, Jakobshavn Isbrae, and Humboldt Gletscher, as major contributors to ice loss. Notably, Qajuuttap Sermia in southern Greenland experienced modest growth, but the gains were insufficient to offset losses from other glaciers.
The study’s co-author, JPL cryosphere scientist Alex Gardner, emphasizes the significance of this research, stating, “Previously, we had bits and pieces – lots of local studies. But what this study offers is a systematic and comprehensive view that has led to some pretty significant insights that we didn’t have about the ice sheet before.”
Additionally, the study reveals that glaciers with the most significant seasonal fluctuations in ice front positions exhibit the greatest overall retreat. This correlation suggests that glaciers sensitive to warming during the summer months will be most impacted by climate change in the coming decades.
Source:
Jet Propulsion Laboratory, California Institute of Technology, Nasa Study
Nature: Ubiquitous acceleration in Greenland Ice Sheet calving from 1985 to 2022 (link)