150 Year Record of Freezes Shows Warming Trend
By Cat Lazaroff
MADISON, Wisconsin, September 8, 2000 (ENS) - A 150 year record
of freeze and ice breakup dates for lakes and rivers in locales
as far apart as Wisconsin and Japan chronicles a steady warming
trend.
The report offers more evidence that the Earth is experiencing a
period of global climate change, said the 13 coauthors of the
study, which appears today in the journal "Science."
From sources as diverse as newspaper archives, transportation
ledgers and religious observances, the scientists gathered lake
and river ice records spanning the Northern Hemisphere.
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.
The team's method of gathering information stands in contrast to
the many global warming studies that draw their conclusions from
computer modelling, yet the study's findings are consistent with
those of computer generated models.
The group studied sites ranging from Canada, Europe, Russia,
Japan and the United States. Of those, 38 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 ice breakup
dates.
A smaller collection of records going back in time past 150 years
also show a warming trend, though at a slower rate.
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 very
difficult to refute in any general way."
Magnuson said the observational nature of the study is "both its
strength and its weakness," and the results do not offer specific
proof that greenhouse gases are driving the warming trend.
The findings are consistent with computer generated models that
have been developed to estimate climate change from greenhouse
gases over a 125 year time period, he said.
Greenhouse gases which trap the heat of the sun near the surface
of the Earth are generated by the burning of coal, oil and gas.
These fuels powered the factories of the Industrial Revolution
that spread across Europe and North America from the early 1800s.
The temperature increase could be related to other "drivers" of
climate change, such as fluctuations in solar activity, as well.
The findings also correspond to an air temperature increase of
1.8 degrees Celsius over the past 150 years. A temperature change
of 0.2 degrees Celsius typically translates to a one day change
in freeze and ice breakup 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.
Ice records are valuable to climate researchers, Magnuson said.
They can be gathered across a wide range of the globe, and in
areas traditionally without weather stations. Their primary
weakness is that early observers did not document the methods
used.
"Of course, 10,000 years ago the Midwest was covered by
ice, so we know it's getting warmer," said Magnuson. "What's
troubling and scary to people is that these rates in recent
decades are so much faster."
Climate models have predicted a doubling of total greenhouse
gases in the next 30 years or so, a change that could potentially
move the climate boundaries for fish and other organisms
northward by about 300 miles, about the length of the state of
Wisconsin, Magnuson said.
"This is exciting as a climate indicator because it's a simple,
direct measure of climate change that humans can relate to," said
Magnuson. "Climate change can be relatively abstract, but when
these changes are easily observed in places as familiar as a
nearby lake or river, they become more relevant."
The records in this study are part of a decade long project led
by Magnuson and the University of Wisconsin-Madison Center for
Limnology to build a database of lake and river ice records from
around the world. The project was supported by the National
Science Foundation's Long-Term Ecological Research program, which
emphasizes tracking and understanding global changes.
"It's kind of a new science, you might call it network science,"
Magnuson said. "We reached out to colleagues around the world and
asked for these records. It turned out some people had very rich
stores of data."
The records in this study represent the longest and most intact
of 746 records collected through the project. Some individual
records are of astonishing lengths, with one dating back to the
9th century, another to the 15th century and two more 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 record dating back to the 9th century. Two
churches, one in either country, had a tradition of carrying a
Madonna figure across the lake to the alternate church each year
it froze.
Two other long 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.
Other records included in the study are from lakes Mendota,
Monona and Geneva from Wisconsin; lakes Detroit and Minnetonka
from Minnesota; lakes Oneida from New York and Moosehead from
Maine; Lake Kallavesi from Finland; and the Angara River and Lake
Baikal from eastern Russia.
Another finding in the study, based on the 184 ice records from
1950 to 1995, showed that the variability in freeze and breakup
dates have increased in the last three decades. Magnuson says it
might be related to intensification of global climate drivers
such as the El Nino /La Nina effects in the Pacific Ocean.
"One of the things that we are beginning to do with these types
of data is to separate out the effects of different climate
signals, like El Niņo. We are optimistic that these long and
geographically widespread ice cover records can play some role in
sorting out the effects of greenhouse warming as well," said
Magnuson.
Magnuson says the ecological effects of global warming are only
beginning to be studied. But studies already exist that have
shown the northern ranges of some butterflies and birds have been
extending northward.
Magnuson and colleagues hope to expand on this part of their
analysis in future studies, taking a closer look at interannual
variability, and expanding and updating the database to look at
other climate oscillations. In particular, they would like to
fill in a crucial gap in their study - the last five years.
"We would like to know what has happened with these ice records
in the recent years, especially in light of other climate data
that show a warming trend over this time period," Magnuson said.
The researchers have deposited the compiled data from their study
in a publicly accessible database, with the hope that scientists
and public policy officials will incorporate their findings in
future analyses of global warming.
SOURCE: Environment News Service (ENS)
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