Data support chilling evidence of warming
© Copyright 2000 USA TODAY
September 8, 2000
By Traci Watson
A new study published today says lakes and rivers across the Northern Hemisphere are freezing later and thawing earlier, providing what some scientists say is further evidence that the Earth is warming.
The new results alone don't prove that the planet's temperature is rising, let alone that human activity is causing it. But the new ice data ''are generally consistent with'' other research measuring the human contribution to global warming, the study's authors say.
The study, which appears in the journal Science, relies on records collected from 1846 to 1995 on 26 lakes and rivers, in places ranging from Finland to Japan to Siberia. The study also includes 13 U.S. lakes and rivers, most in Wisconsin, New York and Minnesota.
Over a 100-year span, the lakes and rivers froze 5.8 days later and ice broke up 6.5 days earlier. Data on freezing came from 15 lakes and rivers, data on ice break-up from 24.
Those changes translate to a rise in global air temperature of about 2 degrees per 100 years.
''We'd seen this warming pattern in Madison. (But) so what?'' says lead scientist John Magnuson of the University of Wisconsin.
''The strength of this paper is in pulling all these records together . . . so people could see it was occurring at a more global scale.''
Most scientists think that the planet is heating up and that humans are behind that trend. They cite the 20th-century rise in the burning of fossil fuels, which creates gases that trap heat in the atmosphere.
However, today's results could be explained by increased human activity near the lakes and rivers, says climate researcher Konstantin Vinnikov of the University of Maryland. Deforestation, for example, heats up rivers.
Magnuson says that some of the sites were in wilderness areas and that it's unlikely so many of the records would've showed warming without a change in global climate. That could be caused by human activity, changes in solar energy or a combination of the two.
Others praised the study for providing a valuable new source of long-term climate data. Climate scientists often have to resort to data such as polar ice coverage measured by satellite images, which normally span only a few decades.
The ice data in the new study go back at least 150 years at all 26 sites. At three sites, record keeping began before 1800.
The people who started collecting the ice dates, including Shinto priests, Hudson's Bay Company employees and nature lovers, could have never imagined such a purpose. The ice data for Japan's Lake Suwa, for example, were collected as a marker of the appearance of ice bridges connecting two Shinto temples across the lake from each other.
Other data sets were first collected because rivers and lakes were important trade or transportation routes. Even after highways claimed those roles, people continued to take note of icing or thawing as a sign of the seasons.
''I think these dates were as important to them as airline schedules are today,'' Magnuson says.