Comment: New research shows how rapidly ice sheets retreat Published on: 11 April 2023 Writing for The Conversation, Dr Christine Batchelor and her colleague Dr Frazer Christie discuss what their discovery about the speed of ice sheet retreat may mean for Antarctica. , and , The , which covers an area greater than the US and Mexico combined, holds enough water to raise global sea level by . This would flood hundreds of cities worldwide. And evidence suggests it is melting fast. Satellite observations have revealed that grounded ice (ice that is in contact with the bed beneath it) in coastal areas of West Antarctica has been lost at a rate of in recent years. But the satellite record of ice sheet change is relatively short as there are only 50 years鈥� worth of observations. This limits our understanding of how ice sheets have evolved over longer periods of time, including the maximum speed at which they can retreat and the parts that are most vulnerable to melting. So, we set out to investigate how ice sheets responded during a previous period of climatic warming 鈥� the last 鈥渄eglaciation鈥�. This climate shift occurred between roughly 20,000 and 11,000 years ago and spanned Earth鈥檚 transition from a glacial period, when ice sheets covered large parts of Europe and North America, to the period in which we currently live (called the ). During the last deglaciation, rates of temperature and sea-level rise were broadly comparable to today. So, studying the changes to ice sheets in this period has allowed us to estimate how Earth鈥檚 two remaining ice sheets (Greenland and Antarctica) might respond to an even warmer climate in the future. Our show that ice sheets are capable of retreating in bursts of up to 600 metres per day. This is much faster than has been observed so far from space. Pulses of rapid retreat Our research used of the Norwegian seafloor to identify small landforms called 鈥渃orrugation ridges鈥�. These 1鈥�2 metre high ridges were produced when a former ice sheet retreated during the last deglaciation. Tides lifted the ice sheet . At low tide, the ice sheet rested on the seafloor, which pushed the sediment at the edge of the ice sheet upwards into ridges. Given that there are two low tides each day off Norway, two separate ridges were produced daily. Measuring the space between these ridges enabled us to calculate the pace of the ice sheet鈥檚 retreat. During the last deglaciation, the that we studied underwent pulses of extremely rapid retreat 鈥� at rates between 50 and 600 metres per day. These rates are up to 20 times faster than the highest rate of ice sheet retreat that has so far been measured in Antarctica from satellites. The highest rates of ice sheet retreat occurred across the flattest areas of the ice sheet鈥檚 bed. In flat-bedded areas, only a relatively small amount of melting, of around half a metre per day, is required to instigate a pulse of rapid retreat. Ice sheets in these regions are very lightly attached to their beds and therefore require only minimal amounts of melting to become fully buoyant, which can result in almost instantaneous retreat. However, rapid 鈥渂uoyancy-driven鈥� retreat such as this is probably only sustained over short periods of time 鈥� from days to months 鈥� before a change in the ice sheet bed or ice surface slope farther inland puts the brakes on retreat. This demonstrates how nonlinear, or 鈥減ulsed鈥�, the nature of ice sheet retreat was in the past. This will likely also be the case in the future. A warning from the past Our findings reveal how quickly ice sheets are capable of retreating during periods of climate warming. We suggest that pulses of very rapid retreat, from tens to hundreds of metres per day, could take place across flat-bedded parts of the Antarctic Ice Sheet even under . This has implications for the vast and potentially unstable of West Antarctica. Since scientists began observing ice sheet changes via satellites, Thwaites Glacier has experienced and is now only 4km away from a flat area of its bed. Thwaites Glacier could therefore suffer pulses of rapid retreat in the near future. Ice losses resulting from retreat across this flat region could accelerate the rate at which ice in the rest of the Thwaites drainage basin collapses into the ocean. The Thwaites drainage basin contains enough ice to . The Fimbul Ice Shelf in East Antarctica. Christine Batchelor, Author provided Our results shed new light on how ice sheets interact with their beds over different timescales. can occur over decades to centuries where the bed of an ice sheet deepens inland. But we found that ice sheets on flat regions are most vulnerable to extremely rapid retreat over much shorter timescales. Together with data about the shape of ice sheet beds, incorporating this short-term mechanism of retreat into computer simulations will be critical for accurately predicting rates of ice sheet change and sea-level rise in the future. , Lecturer in Physical Geography, and , Postdoctoral Research Associate, This article is republished from under a Creative Commons license. Read the . 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