The world’s oceans, which have absorbed 90% of the excess heat caused by human activities, are playing a crucial but complex role in climate change. This heat absorption has had a significant impact on Greenland’s ice sheet and shelves, accelerating their melting and contributing to sea-level rise.
Greenland’s ice sheet, resting on land, has already contributed to over 17% of sea level rise between 2006 and 2018. Moreover, the ice shelves of northern Greenland, which float on the ocean, have lost over a third of their volume since 1978 due to warm seawater eroding them from below. This is alarming as these ice shelves act like natural dams, regulating the flow of ice from the interior of the ice sheet into the ocean. Their deterioration leads to increased ice discharge into the ocean, which is a significant contributor to rising sea levels.
A recent study in Nature Communications used satellite data and modeling to examine the health of these ice shelves. Researchers found that the grounding lines, where the ice sheet becomes a floating ice shelf, are retreating inland due to the thinning of ice shelves. This retreat is particularly concerning because of the retrograde bedslope in Greenland, where the ground under the ice gets deeper towards the island’s center. This topography can lead to an unstoppable retreat of the grounding lines, exposing more ice to warm ocean waters, thereby increasing melting and discharge into the ocean.
The melt rates of northern Greenland’s ice shelves have surged since 2000, peaking in 2015, correlating with a rise in ocean temperatures. These findings are crucial for predicting future declines in Greenland’s ice and associated sea-level rise.
Compounding the issue, the Arctic region, including Greenland, is warming up to four times faster than the rest of the planet. This increased air temperature, along with higher ocean temperatures, is accelerating ice melt from both above and below. Additionally, the diminishing sea ice, which acts as a protective buffer for ice shelves, poses another threat to these structures.
Antarctica is experiencing similar challenges, with its ice shelves also being eroded by relatively warm seawater. This erosion is causing the retreat of grounding lines and accelerating the decline of its ice sheets.
The study underscores the multiple factors contributing to the degradation of Greenland’s ice sheet: higher air and ocean temperatures, decreasing sea ice, and weakening ice shelves. This complex interplay of factors is leading to faster glacier flows into the sea, a process that could have a profound impact on global sea levels.
https://www.wired.com/story/a-major-alarm-is-flashing-under-greenlands-ice/