AMHERST, Mass. - Five University of Massachusetts researchers, including a professor, a staff researcher, and three former graduate students, are among the group of scientists who have found that the Arctic region is getting warmer. The research is detailed in the Nov. 14 issue of Science.
Raymond Bradley, chair of the UMass geosciences department and one of the authors of the Science article, notes that weather instruments have been widely available for only the past few decades. This means that scientists who want to study climates previous to the advent of weather instruments must rely on "natural archives." These include lake sediments, ice core samples, and tree rings. These samples, analyzed in laboratories, reveal clues about environmental conditions of the past, enabling scientists to map out climate changes in the Arctic going back for four centuries – and in some cases, as far back as several thousand years. Taking a variety of samples allowed scientists to cover a broad geographic area and to cross-check their findings, according to Bradley.
"Before these studies began, we had only a few decades of instrumental measurements from the Arctic, so our view of climate variations in the region was very limited," said Bradley. "By extending the climate record through the use of these natural recorders of climate, we were able to place the recent changes in a longer term perspective." The five-year effort required UMass scientists to travel to two separate sites, roughly 100 miles apart, on Ellesmere Island, just west of Greenland. Some of the research sites were just seven degrees in latitude from the North Pole, or about 450 miles from the top of the world.
The UMass team’s contribution was in studying microscopically thin layers of sediment from the bottom of three Arctic lakes. A new layer is formed each summer, and another each winter. The thickness of the layers, and the materials contained in them, tell scientists about the area’s history of precipitation and temperature. Working from the surface of frozen lakes, the UMass team extracted samples of the layered sediments from beneath as much as 400 feet of water, coring approximately six feet into the lake beds. These cores were then cut extremely thinly and examined beneath a microscope. UMass researchers included Bradley, postdoctoral research associate Douglas Hardy, and alumni Michael Retelle, Scott Lamoureux, and Sheldon Smith. Retelle holds a doctorate from the University, Lamoureux and Smith hold master’s degrees.
The group’s results suggest that a combination of natural and human factors are responsible for the unprecedented changes in the Arctic environment. Natural factors may include increased energy from the sun, decreased volcanic activity, and factors within the climate system. In addition, the increasing concentration of greenhouse gases resulting from human activity may have supplemented the natural factors, scientists say. The changes scientists have documented in the Arctic climate fall in line with global warming predictions, as well as the expected environmental response to increased greenhouse gas concentrations. Arctic warming has already had dramatic effects on the area, causing glacial retreats, and the melting of permafrost and sea ice, as well as changing the terrestrial and lake ecosystems, Bradley says.
From the mid-19th century to the mid-20th century, and particularly after 1920, the Arctic warmed to its highest summertime temperatures in at least 400 years, according to researchers. While the warming has been relatively slight – up just 1 to 1.5 degrees Celsius(or about 1.5 to 2.5 degrees Fahrenheit) – even a slight change in summer temperature can have a major effect in the Arctic, Hardy notes. In the region where the UMass scientists worked, the average temperature between June and August is currently only 0.9 degrees Celsius, so a slight rise in the average temperature can mean many more days with temperatures above freezing.
The project was conducted along with researchers from other institutions, including the University of Colorado, the University of California Los Angeles, the University of Toronto, the University of Alaska, the University of Ottawa, Columbia University, the University of Alberta, the University of New Hampshire, Bates College, and the National Oceanographic and Atmospheric Administration. Much of the research was funded by the National Science Foundation through its Arctic System Science Paleoclimates of Arctic Lakes and Estuaries Initiative.