In a paper first-authored by Aaron K. Medford of the University of Maine, the team detailed its radiocarbon dating of plant remains uncovered as the ice cap has recently retreated. Their results suggest that moss and willow shrubs grew near the present boundary of the glacier during two very recent periods—the first being roughly 1000 years ago, and the second being roughly 500 years ago.
“The oldest ages are [approximately] 900-1000 [years old],” the scientists wrote in the paper, published in April in Quaternary Science Reviews. “Thus, when these plants lived, Renland Ice Cap must have been smaller than it was in A.D. 2011, allowing plants to grow in spaces that until recently have been covered by ice.”
The first period of speculated warming roughly corresponds to the Medieval Optimum, a warm period during which Viking explorers reached Greenland and the North American continent.
By studying sediments from lakes fed by the glacier, the researchers inferred that the Renland Ice Cap was smaller than it is today roughly 9,500 years ago, as well as during a period from roughly 7,000 to 4,000 years ago.
Kenneth Richard of Climate Depot highlighted the study, arguing that it supports the view that the Early Holocene, dated from roughly 12,000 years ago to roughly 8,500 years ago, and the Middle Holocene, dated from roughly 8,500 years ago to 4,200 years ago, were warmer than current temperatures in eastern Greenland, as well as the view that current ice coverage and temperatures are still consistent with a Holocene “cold stage.”
Medford and his team noted that their findings were consistent with other proxies for temperature in the region, including insect remains from Last Chance Lake near Scoresby Sund. The latter data “indicate warmer summer temperatures than today throughout the early and most of the middle Holocene,” the authors wrote.
In 2004, an international team reviewed paleoenvironmental data, including pollen macrofossils and various other proxies, from sites spanning the western Arctic. 120 of the 140 locations that they surveyed “provided clear evidence for warmer-than-present conditions,” supporting the existence of a regional Holocene Thermal Maximum during the Early Holocene.
In its 2007 Fourth Assessment Report (AR4), the Intergovernmental Panel on Climate Change (IPCC) noted that records from the North Atlantic, the Arctic, and other regions “provide evidence for local multi-centennial periods warmer than the last decades by up to several degrees in the early to mid-Holocene.”
Yet the IPCC emphasized that the extent and precision of proxy data “limit the ability to determine if there were multi-decadal periods of global warmth comparable to the last half of the 20th century.”
Summarizing recent studies, the IPCC’s 2013 Fifth Assessment Report noted that the mid to high latitudes of the Southern Hemisphere may have exhibited a cooling trend over the course of the Holocene, while the Northern Hemisphere’s mid to high latitudes may have been one degree Celsius warmer than current temperatures roughly 6,000 to 8,000 years ago.
The report, which also noted with “high confidence” that many glaciers were at times smaller than during the late 20th century in the Alps, Scandinavia, Greenland, Baffin Island, and Spitsbergen, concluded that mean Northern Hemisphere temperature between 1983 and 2012 marked it as “very likely the warmest 30-year period of the last 800 years (high confidence) and likely the warmest 30-year period of the last 1,400 years (medium confidence)” in that region.
The plant remains uncovered in eastern Greenland aren’t the first to emerge after several centuries on ice. On Ellesmere Island in northern Canada, mosses that had been covered in ice for 400 or more years started to regrow after emerging from a shrinking glacier in 2013.