Nicolas van Nieuwenhove,The waters of the Fram Strait, which runs between Greenland and the Arctic archipelago of Svalbard, have warmed roughly 3.5 degrees Fahrenheit over the past 100 years, the study’s authors said. The water temperatures are about 2.5 degrees higher than during the Medieval Warm Period, a time of elevated warmth from A.D. 900 to 1300.
The findings are another indication that recent global warming is atypical in the context of historical climate fluctuations, said Thomas Marchitto, a paleoclimatologist at the University of Colorado, Boulder, and a co-author of the study.
“It doesn’t necessarily prove that the change that we see is man-made, but it does strongly point toward this being an unusual event,” Dr. Marchitto said. “On a scale of 2,000 years, it stands out dramatically as something that does not look natural.”
The scientists used cores of ocean sediment containing fossils of microscopic shelled organisms called foraminifera to reconstruct past water temperatures in the strait. They found that the abundance of a species of warmer-water foraminifera rose sharply in the last 100 years, becoming dominant over a cold-water variety for the first time in 2,000 years.
The scientists also tested the shells for levels of magnesium, which rise in tandem with water temperature.
“Both of those approaches gave us the same answers,” Dr. Marchitto said.
Scientists called the study yet another validation of the so-called “hockey stick” graph, a historical reconstruction of global temperatures first published in the late 1990s that showed a steep rise in temperatures in modern times.
“It’s one more piece of evidence that the past 100 years has been an anomaly,” Joshua Willis, an oceanographer at the Jet Propulsion Laboratory in Pasadena, Calif., told a science writer with the journal Nature.
The hockey stick graph has long been a target of climate skeptics, who assert that temperatures during the Medieval Warm Period, when vineyards were planted in England and southern Greenland was settled by Norse colonists, were probably higher than they are today. Were temperatures higher in the past, skeptics argue, then recent warming is more likely to be a result of natural variability than a consequence of human activity.