Ice records from 9th century show global warming

A unique study of 39 historic records of when ice appeared and melted on lakes and rivers around the world has confirmed that the planet is now a markedly warmer place than it was 150 years ago.

A unique study of 39 historic records of when ice appeared and melted on lakes and rivers around the world has confirmed that the planet is now a markedly warmer place than it was 150 years ago.

Detailed records of when the first freeze or the first break-up of ice occurred at sites ranging from Canada and Europe to Russia and Japan have revealed a consistent pattern of warming between 1846 and 1995.

Scientists from the University of Wisconsin-Madison found that in the annual cycle the first freeze now comes 8.7 days later, and the first break-up 9.8 days earlier than 150 years ago.

A smaller collection of records going back even further also showed a warming trend, although at a slower rate.

The results, published in the journal Science, support the view that the global warming is the result of the release of carbon dioxide from industrialisation in the 19th century.

John Magnuson, a freshwater biologist at the university and leader of the study, said: "We think this is a very robust observation: it is clearly getting warmer in the northern hemisphere. 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."

The scientists concluded that although the latest data do not prove that global warming is caused by the release of man-made greenhouse gases, such as carbon dioxide, the results are "consistent" with the computer models used to estimate what effect such pollution would have had over 125 years.

Researchers predict a doubling of greenhouse gases over the next 30 years, which could potentially move climate boundaries for fish and other organisms north by 300 miles.

The records investigated by the scientists date back to the 9th century. One set, from the 15th century, was collected by Shinto monks at Lake Suwa in Japan, where ice was thought to allow two deities, one male and one female, to come together. Another was from two churches next to Lake Constance on the German-Swiss border, where the ice was crossed to carry a Madonna figure from one church to the other.

Ice records were also kept on the Red and McKenzie rivers in Canada to monitor open water for fur trading from the 1700s.