The Earth is constantly shaped by fire and ice, and not in a poetic sense. These physical forces scorch or sweep across the surface of our planet with fiery eruptions or the unstoppable advance of glaciers. On the cold side, the Earth has experienced at least five ice ages, including some possible snowball or sleet episodes if we go deeper in time. We are indeed in a geological ice age right now, but we are currently in a warmer interglacial period, which began about 11,700 years ago, around the time many furry megafauna began to go extinct. These warmer periods fluctuate with colder, frigid periods hosting large glaciers, what we colloquially call “ice ages” and associate with woolly mammoths and shivering cave dwellers huddled over sparse fires. Our hot and cold history. (Dragons Flight/Wikimedia Commons/CC BY-SA 3.0) In reality, the next of these ice ages may have begun about 2,000 years ago, only to be interrupted by human-driven climate change, suggests a new study published in the journal Science. “It was just beginning, everything was normal, the next ice age was about to happen, and yet it stopped,” says Nicolas Young, a geochemist at Columbia University and first author of the study. in the Laurentide Ice Sheet (LIS), the largest structure of its kind from the Pleistocene, which covered much of the northern US and Canada around 95,000 to 20,000 years ago. At its maximum, it extended its icy domain from the Arctic Circle to Illinois, covering these ancient lands with up to 3 kilometers (2 miles) of ice. Its total ice volume may have been equivalent to around 80 meters (260 ft) of sea level change. The LIS became the majestic Barnes Ice Cap (BIC), the small but still beating heart of an entire ice age, the researchers suggest. The boundary of the Barnes Ice Cap (BIC), whose bedrock has only been revealed in the last decade, researchers say. (Nicolas Young) To reach that conclusion, the researchers created a chronology of the ice sheet using two main lines of in situ evidence, based on atomic dating methods. They focused on different types of rocks to measure the proportion of cosmogenic beryllium-10, an isotope (atomic variant) of the element beryllium. It occurs when cosmic radiation from huge exploding stars hits our planet. They also analyzed long-dead vegetation revealed as the BIC retreated, to measure the proportion of carbon-14, a benignly radioactive carbon with a predictable decay rate. Both measurements act as terrestrial chronometers. In rocks, the accumulation of beryllium-10 stops when the advance of glaciation protects the stones from the invisible bombardment of the Universe. Accumulation resumes when rocks are exposed as the ice retreats. For plants, the carbon timer begins when they are trapped under advancing ice, because dead vegetation no longer inhales carbon. The BIC and its revealing finish from the 1960s. (Nicolás Young) Together, the researchers put together a concise chain of climate change. The highest temperatures of our current interglacial period, called the Holocene, may have occurred around 11,000 to 10,000 years ago – at least in northern climates – driven by high solar irradiance due to the change in Earth’s orbit, known as “Milankovitch cycles.” The following millennia welcomed a cooling trend, but surprisingly, the LIS continued to shrink because its surface had sunk too much to continue growing, leaving it out of step with the climate. By 3,600 years ago, it had shrunk to a smaller size than it is today, and remained at that minimum until about 2,000 years ago. It was not until about 2,000 years ago that it began to expand, representing the beginning of the next ice age. rather, the starting point of a possible ice age, if not for the influence of warming summer temperatures starting in the 1960s, the researchers suggest. They report that the BIC reached its all-time high around 1960. Then, with its frozen mind presumably bent on world domination, anthropogenic warming reversed its growth, tilting it toward a negative mass balance, melting faster in the warm months than it could recover in the winter. Since then, their losses “can be explained almost entirely by rising summer temperatures,” which are shrinking other ice sheets in the Canadian Arctic and North Atlantic, the researchers say, in a culmination of rising greenhouse gas emissions dating back to around 1750. Around this time, the Industrial Revolution began to significantly pollute our atmosphere with greenhouse gases. 1780 to 1880. But what about the future? Models suggest that the old LIS, or the current BIC, or some future combination of these two terms, will be gone forever based on current climate profiles, a vestige of an old world lost forever. “Those will be the true last remains of Laurentide, disappearing forever,” Young concludes. “What had been an extremely natural and predictable phenomenon no longer exists.” The research has been published in Science. This article was fact-checked by Peter Dockrill and edited by Peter Dockrill. While we take pride in our process, we are human. If you spot an error, please let us know.
