According to a new international study, water flowing into the Arctic Ocean from the North Atlantic is the warmest it has been in the past 2,000 years. The study was based on work done by professors at the University of Colorado Boulder and was led by Robert Spielhagen of the Academy of Sciences, Humanities, and Literature in Germany. Findings showed that average water temperature in the Fram Strait – which runs between Greenland and Svalbard, an archipelago that makes up the northernmost extent of Norway – has risen 3.5 degrees Fahrenheit in the past century.
Today’s water temperatures are roughly 2.5 degrees F above what they were during the Medieval Warm Period, which affected the North Atlantic from about 900 – 1300 A.D. and altered the climates of Northern Europe and northern North America. The authors of the study hypothesize that this recent rise in water temperature in the Fram Strait is related to the amplification of global warming in the Arctic.
The CU-Boulder’s National Snow and Ice Data Center estimate that between 1979 and 2009, the total loss of Arctic Sea ice extent was larger in area than the state of Alaska. Such findings have led some scientists to predict that within the coming decades, the Arctic will be ice-free during summer months.
Based on their studies, the team of researchers behind the study believes that a number of recent trends (including the rapid warming of the Arctic, the loss of Arctic sea ice, and the warming of the North Atlantic) are interrelated. The new data and observations from the study allow the scientific community and the public to view the current warming trend in the North Atlantic in a new context. Specifically, the study offers substantial evidence that water temperatures in the Fram Strait fall well outside natural bounds of the past 2000 years. The weighty implication of this finding is that warmer temperatures in waters surrounding the Fram Strait may not fall within natural temperature fluctuations either.
According to Thomas Marchitto, paleoclimatologist at UC-Boulder and co-author of the new study, positive feedbacks between ice cover, the Arctic Ocean and the atmosphere could be accelerating the rate of Arctic sea ice decline. As temperatures rise, ice cover declines, the ocean absorbs more solar heat, and warmer water temperatures result in the further loss of ice cover.
Sea ice is critical in cooling the planet by reflecting sunlight back into space; however, cold seawater is crucial for the formation of sea ice, which is one of the reasons the recent findings are so alarming. In contributing to major loss of sea ice, warmer waters could lead to drastic changes in the Arctic, which in turn could have huge implications for the climates of Europe and North America.
The question that is inevitably asked when potentially catastrophic climatic scenarios are discussed is how scientists determine whether or not changes are anthropogenic or the result of natural variability. To address such doubts, the CU-Boulder team took core samples of ocean sediment dating back 2,000 years in order to determine past water temperatures. Researchers used foraminifera – microscopic, shelled protozoan organisms that thrive at specific water temperatures – as proxy historic thermometers. The team also used chemical analysis of foraminifer shells as a second, independent means of reconstructing temperature trends. Both methods demonstrated a sharp rise in the abundance of warmer-water foraminifera in the last 100 years; for the first time in 2,000 years, this species became dominant over a cold-water variety.
These findings are yet another indication that recent warming trends are atypical of historic climate fluctuations. Scientists who worked on the study say that the findings are also corroboration of the ‘hockey-stick’ graph, which was first published in the 1990s and showed a steep temperature rise in modern times.
Warming of Arctic waters also has implications beyond the Arctic climate and the loss of arctic sea ice. As a result of melting land ice and warmer seawater, the volume of the ocean is increasing. Some new studies offer persuasive evidence that after remaining fairly stable for the last 2000 years, the volume of the ocean began to rise only recently in conjunction with industrialization. Such observations suggest that sea level itself may be sensitive to the accumulation of atmospheric greenhouse gasses.
While the scientific jury is still out on how much of current oceanic trends can be attributed to human activity, a co-author of the CU-Boulder study recently stated he feels “fairly confident that what we are seeing today is largely an anthropogenic signal”. For those who accept this as true, the question now becomes what humans can do to reverse (or at least mitigate) such changes.
For a first-hand account of the process of carrying out climate change research at the poles, see this ongoing series of blog posts by scientists from Columbia’s Lamont-Doherty Earth Observatory, as they mount a geological study along the edges of the Antarctic ice sheet.