A new report from researchers from York University and the University of Wisconsin reveals the oldest inland water ice records in human history and the first documented evidence of global warming, revealing ancient trends toward ice-cover formation and earlier spring thaw since the beginning of the Industrial Revolution.
"These data are unique," said Sapna Sharma, a York University biologist and co-lead author of the study. "They were collected by humans viewing and recording the ice event year after year for centuries, well before climate change was even a topic of discussion."
Part of the data stems from records of Japan's Lake Suwa taken by Shinto priests, who conducted the analysis in an attempt to observed a legend about a male god who crossed the frozen lake to reach a female god. The other part stems from a local Finnish merchant who began collecting data on Finland's Torne River because its frozen or thawed status had important implications for trade, transportation and food acquisition.
Ice seasonality - whether a lake or river freezes over in the winter or thaws again in the spring - is strongly connected to climate and the trends revealed from the newly observed data are telling.
"Even though the two waters are half a world apart and differ greatly from one another, the general patterns of ice seasonality are similar for both systems," said John Magnuson, a University of Wisconsin limnologist and co-lead author of the study.
The study reveals that from 1443 to 1683, Lake Suwa's annual freeze data was moving to later in the year at a rate of 0.19 days per decade, a trend that eventually grew 24 times faster to 4.6 days per decade. Meanwhile, on the Torne River, similar findings revealed earlier ice breakup in the spring and a double in the speed that the river experienced earlier thaw dates. Together, the findings suggest rapid climate change during the last two centuries.
In terms of recent data, both waters have shown extreme ice dates that suggest increased warming - Lake Suwa experienced more years without full ice cover occurring, and Torne River has experienced extremely early ice breakup.
"Our findings not only bolster what scientists have been saying for decades, but they also bring to the forefront the implications of reduced ice cover," Sharma said, pointing to its effects on ecology, culture and economy. "Decreasing ice cover erodes the 'sense of place' that winter provides to many cultures, with potential loss of winter activities such as ice fishing, skiing, and transportation."
The findings were published in the April 26 issue of Scientific Reports.
