April 30 (Bloomberg) -- The world's largest lake is warming faster than the atmosphere, challenging the idea that large bodies of water can withstand global warming, according to U.S. and Russian scientists.

Siberia's Lake Baikal, which holds 20 percent of the world's fresh water, has warmed by 1.21 degrees Celsius (2.16 degrees Fahrenheit) since 1946, said Marianne Moore, assistant professor of biological sciences at Wellesley College in Massachusetts. Global temperatures have risen 0.76 degrees Celsius since industrialization, a UN panel on climate change said in March.

The lake holds more than 2,500 plant and animal species, including the world's only exclusively freshwater seal, and some could become extinct by continued warming, said Moore, co-author of a report on Lake Baikal to be published in May in the journal Global Change Biology. The study challenges the idea that thermal inertia of oceans, seas and large lakes would make them more resistant to climate change, Moore said.

``The warming that we're seeing in this lake is of more concern than that of any other lake because of the extraordinary biodiversity,'' Moore said in an interview. ``You could potentially lose the Baikal seal.''

Carbon dioxide, produced mainly from burning petroleum fuels, is the chief pollutant blamed for global warming. Rising global temperatures driven by human emissions of greenhouse gases is causing Arctic ice to melt and rain to decline in parts of Africa and the Mediterranean, according to the UN.

Family Project

Beginning in the 1940s, data on Lake Baikal was collected by Mikhail Kozhov, a professor at Irkutsk State University in Siberia. The research was carried on by his daughter and granddaughter, Lyubov Izmest'eva, a co-author of the journal article.

The family members took samples of the lake every 7 to 10 days since 1946, amassing a history that Moore analyzed using modern statistical techniques. The data revealed that the lake's average summer temperature has increased by 2.4 degrees, Moore said.

``My jaw just dropped to the floor when I hear this,'' Moore said. ``I was extremely surprised that the data set even existed.''

Lake Baikal is the world's deepest lake and holds more water than all of the U.S. Great Lakes combined. It's also the oldest, dating back 25 million years, predating humans.

Warming has reduced the amount of time the lake is frozen in winter, threatening the seal and other species that depend on the ice to hunt. In 1996, the UN Educational, Scientific and Cultural Organization declared Baikal a ``World Heritage Site'' because of its biological diversity.

``The predictions are that that lake is going to lose ice each year by another two weeks to two months in this century,'' Moore said. ``If that happens, that is going to hammer the bottom and the top of the food chain.''

To contact the reporter on this story: Jim Efstathiou Jr. in New York at jefstathiou@bloomberg.net.

Last Updated: April 30, 2008 16:33 EDT