Mer oppvarming. Merk fra nedenstående:
""Of course, 10,000 years ago the Midwest was covered by ice, so we know it's
getting warmer," he says. "What's troubling and scary to people is that
these rates in recent decades are so much faster.""
Karsten Johansen
http://www.newswise.com/articles/2000/9/LAKEICE.UWI.html
EMBARGOED FOR RELEASE AT 2 P.M. EASTERN TIME, THURSDAY, SEPT. 7, 2000
CONTACT: John Magnuson, (608) 262-3014; jmagnuson@mhub.limnology.wisc.edu
NOTE TO PHOTO EDITORS: High-resolution images to accompany this story may be
downloaded at: http://www.news.wisc.edu/newsphotos/lakeice.html
150-YEAR GLOBAL ICE RECORD REVEALS MAJOR WARMING TREND
MADISON - From sources as diverse as newspaper archives, transportation
ledgers and religious observances, scientists have amassed lake and river
ice records spanning the Northern Hemisphere that show a steady 150-year
warming trend.
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, to be published in the Sept. 8 issue of the journal Science.
Sites ranges from Canada, Europe, Russia and Japan. 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 breakup
dates. A smaller collection of records going well past 150 years also show a
warming trend, at a slower rate.
"We think this is a very robust observation: It is clearly getting warmer in
the Northern Hemisphere," says 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 says 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. However, 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 says.
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 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.
Ice records have valuable attributes for climate researchers, Magnuson says.
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," he says. "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,
approximately the length of the state of Wisconsin, Magnuson says.
The records in this study are part of a decade-long project led by Magnuson
and the UW-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
says. "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
peculiar 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 the variability in freeze and breakup dates 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.
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.
# # # --- Brian Mattmiller, (608) 262-9772; bsmattmi@facstaff.wisc.edu
Researchers who contributed to this study include: Dale Robertson at U.S.
Geological Survey, Middleton, Wis.; Barbara J. Benson at UW-Madison;
Randolph Wynne at Virginia Polytechnic Institute and State University,
Blacksburg; David Livingstone at Swiss Federal Institute of Environmental
Science and Technology, D?bendorf, Switzerland; Tadashi Arai at Rissho
University, Tokyo, Japan; Raymond Assel at National Oceanic and Atmospheric
Agency, Ann Arbor, Mich.; Roger Barry at University of Colorado, Boulder;
Virginia Card at Metropolitan State University, St. Paul, Minn.; Esko
Kuusisto at Finnish Enivronment Institute, Helsinki, Finland; Nick Granin at
Limnological Institute, Irkutsk, Russia; Terry Prowse at Environment Canada,
Saskatoon; Kenton Stewart at State University of New York at Buffalo; and
Valery Vuglinski at State Hydrological Institute, St. Petersburg, Russia.
This archive was generated by hypermail 2b29 : Tue Oct 17 2000 - 17:39:59 MET DST