--- title: "Laurentide Ice Sheet's Unexpected Reversal in Size Challenged Climate History Understanding" url: https://noti.group/laurentide-ice-sheet-s-unexpected-reversal-in-size-challenged-climate/ language: en publisher: "Noti Group" section: "Technology" published: 2026-10-24T11:00:09.000Z updated: 2026-10-24T16:50:00.155Z id: c6cd0afc-f77b-47df-961b-ebe748edd9dd source: "Ars Technica https://arstechnica.com/science/2026/10/ice-sheet-expansion-may-have-started-2000-years-go-but-we-canceled-that/" attribution: "Link to https://noti.group/laurentide-ice-sheet-s-unexpected-reversal-in-size-challenged-climate/ and name Noti Group when you quote or summarize this story." --- # Laurentide Ice Sheet's Unexpected Reversal in Size Challenged Climate History Understanding A new study published in Science reveals that the Laurentide Ice Sheet, which once covered most of Canada under a blanket of ice two miles thick, reached its smallest size approximately 3,600 years ago before starting to expand again around 2,000 years later. The remnants of the Laurentide Ice Sheet, which once covered most of Canada under a blanket of ice two miles thick, have yielded new evidence that challenges our understanding of climate history. Researchers have found that this massive ice sheet reached its smallest size approximately 3,600 years ago before starting to expand again around 2,000 years later. According to the study published in Science, this unexpected reversal suggests that a new glaciation may have been underway until it was halted by human-caused climate warming around 1960. The researchers' interpretation of their findings indicates that the Laurentide Ice Sheet was on the verge of advancing once more before it was stopped in its tracks. The Barnes Ice Cap, located on Baffin Island, is the last surviving fragment of the Laurentide's central dome. This remnant has provided critical insights into the ice sheet's history due to its unique geological characteristics. The researchers attribute this knowledge-gaining capability to the temperature at the base of the cap. The study's lead author, Nicolás Young, a geologist from Columbia University's Lamont-Doherty Earth Observatory, notes that the Barnes Ice Cap is the deflated core of what was once an enormous dome of ice two miles thick. The team's findings suggest that this massive ice sheet had retreated and then begun to re-grow approximately 2,000 years ago. The implications of these findings are significant, as they challenge our understanding of climate history and potentially alter our perspectives on the future of glaciation. However, more research is needed to fully grasp the extent of this phenomenon and its connection to current global climate trends. Research on ancient ice sheets has revealed a surprising phenomenon: the expansion of ice sheets may not be a recent occurrence. In contrast to most glaciers, which are warm-based and slide over their beds due to meltwater, the Barnes Ice Cap is cold-based, meaning it freezes directly onto the bedrock beneath it. This prevents it from sliding and erasing the record of what lies beneath. The unique behavior of cold-based ice was explained by Dr. Young, who noted that such ice acts like a sticker, sticking firmly to whatever surface it's on. A common example of this phenomenon is the formation of ice on car windshields during winter storms. As the Laurentide Ice Sheet retreated across the plateau, tundra plants colonized the newly exposed ground. When the ice sheet re-expanded later, it preserved these plants in place, holding them intact for two millennia. To pinpoint the exact moment when the ice sheet's expansion began, researchers used two independent dating methods. The first method involved measuring beryllium-10, an isotope that accumulates on rock surfaces exposed to the sky. The second dating method looked at dead plant remains, including mosses that had been rooted in the ground before being killed by the expanding ice sheet's margin. The team's radiocarbon dating method allowed them to pinpoint the exact moment when mosses died as the ice sheet advanced, providing crucial information for reconstructing the history of the ice margin. By analyzing multiple kill dates from different locations, scientists were able to create a map of the advancing ice margin. This process revealed a consistent pattern, with most radiocarbon dates clustering around 1800 CE, marking the peak of the Little Ice Age in the Northern Hemisphere. The Little Ice Age saw glaciers reach their maximum extent in recent millennia, and at Barnes, researchers believe this was just one late surge within an ongoing advance that had been underway for nearly two thousand years. This theory suggests a gradual expansion rather than a sudden event. To further investigate the timing of ice sheet expansion, Young's team turned to neighboring ice caps on the same plateau. These smaller ice caps share a similar climate with Barnes and have provided almost 200 kill dates from beneath them. Crucially, none of these dates are older than two thousand years. The implications of this research suggest that all nearby ice caps may have started expanding around the same time, roughly two thousand years ago. Given its proximity to these neighboring ice caps, it's likely that Barnes Ice Cap also began advancing at a similar period. The researchers believe that continued retreat of the Barnes Ice Cap may eventually reveal the samples they need to confirm their findings. If they were to return to the site in 20 years, as the ice margin has retreated further, they might be able to collect the plant material from around 2,000 years ago. The study suggests that the re-expansion of the ice sheet was driven by two opposing global forces. One force was the decline in solar energy reaching high northern latitudes, which peaked about 10,000 to 11,000 years ago and has been decreasing ever since. This decrease pushed the planet toward a new ice age. At the same time, atmospheric carbon dioxide levels rose by around 20 parts per million between 8,000 and 2,000 years ago, increasing the greenhouse effect and warming the atmosphere. According to Young, this increase in carbon dioxide had a relatively small impact compared to the drop in insolation and temperatures. The combination of these factors ultimately led to a significant drop in temperatures around 2,000 years ago. This cooling was enough to trigger the re-expansion of ice sheets, despite expectations that the next ice age would be postponed by tens of thousands of years. Young points out that there is no inherent contradiction between their findings and previous models, which suggested that orbital forcings and carbon dioxide levels would delay the onset of a new ice age. Instead, his team's data simply highlight the complex interplay of factors driving climate change. The definition of glacial inception has traditionally been tied to the size of glaciers and ice sheets, with scientists considering them to be in a new phase when they reach a certain threshold. This approach is reasonable given the lack of data on when an ice sheet first begins to expand. However, recent research has shed light on this process by analyzing geological evidence from the Laurentide ice sheet. It appears that human activities coincided with the re-expansion of this ice sheet, which had previously been in decline. Greenhouse gas levels have risen dramatically since the Industrial Revolution, with concentrations increasing by around 12 ppm between 1750 and 1850, another 50 ppm by 1960, and a further 138 ppm by 2024. This rapid increase in carbon dioxide has had a profound impact on the planet's climate. The consequences of this warming trend can be seen in the decline of the Barnes Ice Cap, which has lost its accumulation zone due to rising temperatures. In the summer months, the ice cap now melts entirely, with no new ice forming to replace it. According to Dr. Young, living through an ice age climate would be extremely challenging and vastly different from what we experience today. He suggests that by releasing large amounts of greenhouse gases into the atmosphere, humans may have inadvertently interrupted a natural cycle that was thousands of years in the making. This cycle, which has been consistent over the past 2.5 million years, is now believed to have been terminated by human activities and greenhouse gas emissions. --- Source: [Ars Technica](https://arstechnica.com/science/2026/10/ice-sheet-expansion-may-have-started-2000-years-go-but-we-canceled-that/) Published by Noti Group: https://noti.group/laurentide-ice-sheet-s-unexpected-reversal-in-size-challenged-climate/