Summer temperatures on the archipelago of Svalbard, 400 miles north of Norway, are now higher than at any other period in the last 1,800 years, according to a new study in the journal Geology.
“We developed a quantitative record of summer air temperature that indicates that for the past two decades summer temperatures on western Svalbard have been warmer than at any time in (at least) the past 1800 years,” said the study’s lead author, William D’Andrea, a climate scientist at Columbia University’s Lamont-Doherty Earth Observatory. “This is significant because it helps us put the rapid and large changes we’ve seen very recently into a longer context and address the question, ‘How unusual is the recent warming in western Svalbard?’”
The Medieval Warm Period (MWP), a 400-year span of relatively hot climate in the North Atlantic region from about 950 to 1250 A.D. led some to argue that contemporary global warming is a natural occurrence. The climate reconstruction of Svalbard undercuts skeptics who deny evidence that we are scorching the planet with the release of high concentrations of heat-trapping greenhouse gases. Since 1987, summers on Svalbard have been 2 degrees to 2.5 degrees Celsius hotter than they were there during warmest parts of the MWP.
“The Arctic is a key region for studying past climate dynamics because temperature changes are amplified at high northern latitudes, projected future warming is greatest in the Arctic, and there are few long term temperature records to help us understand how the Arctic climate system responded in the past to various forcing and feedback mechanisms, said co-author of the study, Nicholas L Balascio, a Postdoctoral Research Associate at the Climate System Research Center at the University of Massachusetts. “Svalbard is particularly interesting because it is at the northern limit of influence of important North Atlantic Ocean and atmospheric circulation systems so small changes in their behavior will likely cause a significant climate response.”
The researchers also demonstrated that the period of most extensive glacier advance on Svalbard in the last 10,000 years (during another anomalous period the 18th and 19th centuries called “Little Ice Age”) was not characterized by very cold summers; rather, increased wintertime snowfall was responsible for the glacier advances.
Researchers reconstructed summer temperatures by analyzing alkenones, lipid biomarkers preserved in lake sediments. Alkenones are fats produced by certain algae. The algae alter their alkenones in response to the temperature of the water in which they grow. When they die, the fats sink to the bottom and are preserved in sediment. Scientists extract alkenones from ocean and lake sediment cores and use them to reconstruct changes in water temperature through time. Though most Arctic climate records are drawn from ice cores, which only preserve annual layers of cold-season snowfall and temperatures, ocean and sediment cores provide records on summertime temperatures. This is particularly useful to scientists interested in studying places where ice sheets are absent.
“We were able to overcome problems in dating lake sediment records in the High Arctic by identifying volcanic ash layers erupted from Icelandic volcanic eruptions,” said Dr. Balascio. “This record spans important climate periods of the last 2,000 years including the Medieval Climate Anomaly, the Little Ice Age, and 20th century and sheds light on the regional response of summer air temperature during these intervals.”Due to a combination of sea-ice loss and changes in atmospheric and oceanic circulation, climate models from the International Panel on Climate Change 2007 report suggests that Svalbard will warm more than any other landmass on earth by 2100. The National Snow and Ice Data Center reported that sea ice in the broader region was at an all-time low, covering about 1.32 million square miles, or 24 percent, of the surface of the Arctic Ocean. Naturally, the warming temperatures and melting arctic ice caps pose major threats to wildlife in the area.
“The spatial patterns of climate variability over the Holocene have been extremely complex, and there are a great number of research questions that remain unanswered during this interval of Earth’s history,” said Dr. D’Andrea. Though “the data does not attribute the recent warming to human activity… there is an enormous body of research that has linked anthropogenic greenhouse gases to the increase in global temperatures over the past few decades.”
Dr. Balascio added, “as we continue to compile paleoclimate data from different parts of the Arctic, we will be able to more clearly understand spatial patterns in the natural variability of the Arctic climate system and better predict the response of the Arctic to future changes.”
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