September 7, 2000
MADISON, Wisconsin (CNN) -- Records from riverboat captains,
Shinto monks and others dating to the 15th century confirm a
dramatic warming trend in the Earth's recent history, scientists
said Thursday.
Studying climate observations from dozens of sites in the
Northern Hemisphere, an international team of researchers
concluded that temperatures have risen steadily for at least 150
years.
They compiled data on lake and river ice cover from newspaper
articles, business journals and individual diaries, some as far
back as 1443.
Piecing together a historic portrait, the researchers said the
Northern Hemisphere has experienced increasingly shorter winter
seasons since 1840.
"The thing that makes this catchy is that this is a very simple
way of looking at what happened over the last 150 years," said
John Magnuson, lead author of the report, to be published Friday
in the journal Science.
"These are direct observations of people. Some were religious
people, some were fur traders," said Magnuson, a freshwater
expert at the University of Wisconsin in Madison.
They include:
• Holy men in Japan who kept precise records at Lake Suwa, where
deities were believed to have traveled on surface ice.
• Clerics in Central Europe who walked a Madonna statue over Lake
Constance when it first froze each season.
• Fur traders and riverboat skippers in Canada who measured river
ice levels.
The records, which also come from the United States, Russia and
Finland, indicate that lakes and rivers now freeze an average of
8.7 days later and ice cover begins disintegrating 9.8 days
earlier than 150 years ago.
The findings are consistent with an increase in air temperatures
during the time of 1.8 degrees C (almost 4 degrees F). Climate
records confirm a rise of at least 1 degree C (2 degrees F) over
the past century.
The trend corresponds with the rise of the Industrial Revolution.
Yet significant warming takes place well before its peak,
suggesting other causes besides greenhouse gas emissions from
human activities.
"These increases are generally consistent with scenarios for
greenhouse gas-forced climate warming, but they may be related to
other drivers, such as changes in solar activity," wrote Magnuson
and his colleagues in Science.
Reuters contributed to this report.
SOURCE: CNN
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