An historical survey of rivers and lakes in the Northern Hemisphere during the past 150 years shows they have been thawing earlier and freezing later each year, an indication the temperate regions of the world have been warming.
Thirteen researchers from around the world, led by University of Wisconsin-Madison limnologist John Magnuson, contributed to the report, which will be published in the Sept. 8 issue of the weekly journal Science. One of the co-authors is the University of Colorado at Boulder聮s Roger Barry, director of the university-headquartered National Snow and Ice Data Center.
The records in the study came from nine countries, including the United States, Canada, Russia, Japan and several European countries. The sources were as diverse as transportation ledgers, newspaper articles and religious observances. The average rate of change over the 150-year period was nearly nine days later for freeze dates and almost 10 days earlier for ice break-up dates, according to the study.
"It is clearly getting warmer in the Northern Hemisphere," said Magnuson. "The importance of these records is that they come from very simple, direct human observations, making them difficult to refute in any general way."
The research project was supported by the National Science Foundation聮s Division of Environmental Biology.
Some of the individual records collected during the project are extremely long. Lake Suwa in Japan, for example, has a lake ice-off and freeze-up record dating to 1443 that was meticulously kept by the holy people of the Shinto religion. Freeze and thaw dates of the lake were recorded because of the belief that ice allowed deities on either side of the lake 聳 one male, one female 聳 to get together.
Another important finding from the same data base -- gleaned from 184 ice records from 1950 to 1995 -- showed the variability in freeze and break-up rates has increased in the past three decades. That data has been published by researchers at Wisconsin-Madison聮s NSF-funded long term ecological research site. The shift could be due to the increasing influence of El Nino and La Nina events in the Pacific, said Magnuson.
The CU-Boulder-headquartered NSDIC is now making plans to distribute the collection of ice records prepared by Wisconsin-Madison聮s Center for Limnology to the public, according to Florence Fetterer, a project manager for NSIDC. The records include contributions from nine countries and were used by the authors to help research and prepare the Sept. 8 Science paper.
"This is an impressive data set," said Fetterer, who noted the collection consists of ice records for 746 water bodies. Of these, 422 of the records for individual bodies of water are longer than 19 years, 165 are longer than 50 years and 27 are longer than 100 years.
Fetterer, who is leading the development of a method to make the data collection accessible to the public over the Internet, said trends in lake and river ice formation are an important source of temperature information and can provide a valuable record of climate change.
In addition, seasonal records of lake ice formation and break-up dates relate to studies of aquatic ecosystems with important ramifications for recreation, transportation, fishing and freshwater resource management, she said.
"This data collection represents years of painstaking work, and we are delighted to archive it at NSIDC," Fetterer said. The collection is expected to be available to the public by December 2000.
The NSIDC is part of the Cooperative Institute for Research in Environmental Sciences, a joint venture of CU-Boulder and the National Oceanic and Atmospheric Administration. Visit the NSIDC web site: for further information.