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NSF PR 00-56 - September 7, 2000
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Tale of the Ice, Revealed
Records of lake, river, ice across
globe reveal major warming trend
Scientists funded by the National Science Foundation
(NSF) have amassed lake and river ice records spanning
the Northern Hemisphere that show a steady 150-year
warming trend. The records come from sources as diverse
as newspaper archives, transportation ledgers and
The study, which includes 39 records of either freeze
dates or breakup dates from 1846 to 1995, represents
one of the largest and longest records of observable
climate data ever assembled. University of Wisconsin-Madison
limnologist John Magnuson led a team of 13 co-authors
who contributed to the report, published in the September
8 issue of the journal Science.
"This research is important because it humanizes the
impacts of global environmental change by using a
simple measurement that is relevant and meaningful
to the public," says Scott Collins, director of NSF's
long-term ecological research program, which funded
All but one of the 39 ice records, which come from
sites ranging from Canada, Europe, Russia and Japan,
indicate a consistent warming pattern. The average
rate of change over the 150-year period was 8.7 days
later for freeze dates, and 9.8 days earlier for breakup
dates. A smaller collection of records going well
past 150 years also shows a warming trend, but at
a slower rate.
The findings also correspond to an increase in air
temperature over the past 150 years of plus-1.8 degrees
Celsius. A temperature change of 0.2C typically translates
to a one-day change in ice-on and ice-off dates. Freeze
dates were defined in the study as the observed period
the lake or river was completely ice covered; the
breakup date was defined as the last ice breakup observed
before the summer open-water phase.
The records in this study are the longest and most
intact of 746 overall records collected through the
project. Some individual records are of astonishing
lengths, with one dating back to the 9th century.
Another is from the 15th century, and two more date
to the early 1700s. For example, Lake Suwa in Japan
has a record dating back to 1443 that was kept by
holy people of the Shinto religion. The religion had
shrines on either side of the lake. Ice cover was
recorded because of the belief that ice allowed deities
on either side of the lake -- one male, one female
-- to get together.
Lake Constance, a large lake on the border of Germany
and Switzerland, has a peculiar record dating back
to the 9th century, also for religious regions. Two
churches, one in either country, had a tradition of
carrying a Madonna figure across the lake to the alternate
church, each year the lake froze. Two other long-running
records come from Canada's Red and McKenzie Rivers,
which date back to the early 1700s and were kept because
ice cover and open water were critical to the fur
trade. Records from Grand Traverse Bay and Toronto
Harbor, both on the shores of the Great Lakes, reflect
their prominence as shipping ports.
Another finding in the study, based on 184 ice records
from 1950 to 1995, showed that variability in freeze
and breakup dates increased in the last three decades.
Magnuson says that may be related to intensification
of global climate drivers such as the El Nino/La Nina
effects in the Pacific Ocean. The ecological effects
of global warming are only beginning to be studied.
But research has already been done that shows ranges
of some butterflies and birds extending northward.