Weather From the Past

Centuries-Old Records Show Global Warming Trend

Bering Glacier in Alaska has shrunk by 10-12 kilometers in length during the past century, losing 130 square kilometers in area. (Daniel Beltra/Greenpeace/AP Photo)

W A S H I N G T O N, Sept. 7— River captains long dead, 15th-century Japanese priests, and records kept by Swiss believers who liked to carry a statue of the Madonna across a frozen lake confirm that global warming is a real trend, scientists said today.
    An international team of researchers has pieced together records kept from as far back as 1443 to show that temperatures are not only rising — they are changing the way lakes and rivers freeze in the Northern Hemisphere.
     “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 of the University of Wisconsin in Madison, who led the study.
     Many studies conclude that global temperature took a sudden upward turn at around the turn of the last century — when the Industrial Revolution reached its peak and people started pumping so-called greenhouse gases into the atmosphere. 

Holy People, Fur Traders
Climate records confirm a rise of at least 1 degree C (2 degrees F) over the past century or so, and various computer models show a consistent pattern.
     But Magnuson and colleagues wanted to see what effect this warming pattern had on people.
     “These are direct observations of people, five generations of people,” said Magnuson, who specializes in the study of freshwater bodies.
     “Some were religious people, some were fur traders. They have looked out and said ‘the lake, the bay, the river is open today.’”
     For example, holy people of Japan’s Shinto religion kept careful records at Lake Suwa, where deities from shrines on either shore were believed to have used surface ice to visit back and forth.
     At Lake Constance, on the border of Germany and Switzerland, congregations at two churches, one in each country, had a tradition of carrying a Madonna figure back and forth across the lake when it froze. 

Confirming El Niño
In Canada, the shipping and fur trade meant records of river freezing were kept as far back as the early 1700s.
     Writing in the journal Science, Magnuson and colleagues say these and other collected records tell a very clear story — lakes and rivers now freeze an average of 8.7 days later than they did 150 years ago and ice cover starts breaking up 9.8 days earlier.
     These findings correspond to an increase of nearly 4 degrees Fahrenheit (1.8 degrees Celsius) in air temperature over the past 150 years.
     And the records, which also come from Finland, Russia and the northern United States, also correspond with known patterns caused by ocean currents, such as the El Niño Southern Oscillation and the North Atlantic Oscillation, Magnuson said.
     “Yes, it is warming and it’s important to understand why,” Magnuson said. He pointed out that his study does not answer that question.