Melting Ice on the Rocky Mountains Reveals 6000-Year-Old Secret About Earth’s Climate History

About 6,000 years ago, the Greater Yellowstone Ecosystem cradled within its mountains, a lush forest springing with thickets and trees. Then, due to declining summer solar radiation, the forest began to cool, eventually becoming the alpine tundra that exists today. As the mountainous landscape got engulfed in ice, the green of this forest faded away, leaving some of its trees entombed deep in the glacial ice. Recently, some archaeologists exploring the Beartooth Plateau in this ecosystem discovered a woodlot of 30 trees, once part of a 5,900-year-old whitebark pine forest. Buried deep in the icy crypt, the trees tell the mysterious story of melting ice and changing climate, as per the study published in the journal Proceedings of the National Academy of Sciences.

Beartooth Plateau is a segment of the Rocky Mountains, located in southcentral Montana in Wyoming, near Yellowstone National Park. The plateau gets its name from Beartooth Peak, which has the appearance of a bear’s tooth. Famous for its “biscuit board topography,” the plateau is punctuated with scalloped uplands and cliff faces that resemble a tray of biscuits. Its flourishing alpine tundra features striking trails of rugged mountains, hanging valleys, 300 lakes, jagged granite knolls, moraines, and cirques carved by glacial erosion.

The habitat is dotted with groves of conifers, aspen, cottonwoods, lodgepole pine, spruce, and fir. Mossy lichens add brushstrokes on its ancient crystalline rocks that also trap quarries of gold, silver, and platinum. And now these additional 30 trees emerged from melting ice when a team of archaeologists was surveying the Beartooth plateau. The trees were found to be approximately 10,140 feet above sea level, 590 feet higher than the present tree line. Also known as a timberline, a treeline is the boundary or edge of a habitat above which trees cannot grow due to harsh environmental conditions like low temperatures, lack of moisture, and extreme snowpack.

This “offers us a window into past conditions at high elevations,” Cathy Whitlock at Montana State University, told New Scientist, “Whitebark pines don’t grow at this elevation now, so these ones had to grow at a time when the climate was warmer.” To unleash the mystery of this lost forest, Whitlock and her team sampled eleven tree rings and analyzed them with radiocarbon dating. They found that the trees thrived 5,950 to 5,440 years ago, a period when temperature began to lower at a rapid scale.

The team also included the data from Arctic ice core samples in their research, mainly to understand what the climate looked like during this period, also known as the “mid-Holocene.” The data suggested that the falling temperature was attributed to massive volcanic eruptions in the northern hemisphere. As these volcanoes erupted, they spewed so much debris and lava that this material blocked sunlight from reaching the forest, causing the temperature to drop. Eventually, the forest became so cool that its trees got buried under icy gulches and sags.

For the next 5,000 years, the trees lay flat and entombed in ice, protected from the elements, which makes them a “valuable time capsule,” as paleoclimatologist Kevin Anchukaitis told New Scientist. “The plateau seems to have been the perfect place to allow for ice patches to establish and persist for thousands of years,” said lead author Greg Pederson, in a statement. This vestige of ancient forest also reveals a motley of insights about climate change and how it is spurring the risk of wildfires in this region. “While such discoveries are scientifically interesting, they are also a sad reminder of how fragile alpine ecosystems are to climate change.”