The Heat Is Online

High Arctic summer temperatures not matched in 1,800 years

Norwegian Arctic Summers Warmest in 1,800 Years

Yale Environment 360, Sept. 30, 2012

Summer temperatures on the Norwegian archipelago of Svalbard in the High Arctic are now higher than during any time over the last 1,800 years, including a period of higher temperatures in the northern hemisphere known as the Medieval Warm Period, according to a new study. In an analysis of algae buried in deep lake sediments, a team of scientists calculated that summer temperatures in Svalbard since 1987 have been 2 to 2.5 degrees Celsius (3.6 to 4.5 degrees F) warmer than during the Medieval Warm Period, which lasted from roughly 950 to 1250 AD.

Scientists say this year's record declines in Arctic sea ice extent and volume are powerful evidence that the giant cap of ice at the top of the planet is on a trajectory to largely disappear in summer within a decade or two, with profound global consequences.

The Medieval Warm Period is often cited by climate change skeptics as proof that the planet has experienced periods of high temperatures in recent centuries unrelated to the burning of fossil fuels. "Our record indicates that recent summer temperatures on Svalbard are greater than even the warmest periods at that time," said William D'Andrea, a climate scientist at Columbia University. The algae, which make more unsaturated fats in colder periods and more saturated fats in warmer periods, reveal critical clues about past climates.

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Mild Little Ice Age and unprecedented recent warmth in an 1800 year lake sediment record from Svalbard

Abstract

The Arctic region is subject to a great amplitude of climate variability and is currently undergoing large-scale changes due in part to anthropogenic global warming. Accurate projections of future change depend on anticipating the response of the Arctic climate system to forcing, and understanding how the response to human forcing will interact with natural climate variations. The Svalbard Archipelago occupies an important location for studying patterns and causes of Arctic climate variability; however, available paleoclimate records from Svalbard are of restricted use due to limitations of existing climate proxies. Here we present a sub-decadal- to multidecadal-scale record of summer temperature for the past 1800 yr from lake sediments of Kongressvatnet on West Spitsbergen, Svalbard, based on the first instrumental calibration of the alkenone paleothermometer. The age model for the High Arctic lake sediments is based on 210Pb, plutonium activity, and the first application of tephrochronology to lake sediments in this region. We find that the summer warmth of the past 50 yr recorded in both the instrumental and alkenone records was unmatched in West Spitsbergen in the course of the past 1800 yr, including during the Medieval Climate Anomaly, and that summers during the Little Ice Age (LIA) of the 18th and 19th centuries on Svalbard were not particularly cold, even though glaciers occupied their maximum Holocene extent. Our results suggest that increased wintertime precipitation, rather than cold temperatures, was responsible for LIA glaciations on Svalbard and that increased heat transport into the Arctic via the West Spitsbergen Current began ca. A.D. 1600.

© Geological Society of America

http://geology.gsapubs.org/content/early/2012/09/18/G33365.1.abstract