She got in touch with Dr. Hamilton, who is an expert in the analysis of complex ecological field data, particularly the use of statistical techniques to discern real trends in the messy ups and downs of nature. The center in Santa Barbara financed the collaboration.

Baikal is a place of unusual biodiversity, with many species found nowhere else. Among them are giant shrimp, bright green sponges that grow in shallow water forests and the Baikal seal, the world’s only exclusively freshwater seal. In 1996, the United Nations Educational, Scientific and Cultural Organization, or Unesco, designated the lake a World Heritage Site.

Although it is known that warming is more intense at high latitudes, as in the Baikal area, and that water is warming in other major lakes, including Lake Tahoe in Nevada and Lake Tanganyika in central Africa, many scientists had thought that Lake Baikal’s enormous volume and unusual water circulation patterns would buffer the effects of global warming.

Instead, the researchers report, surface waters in Lake Baikal are warming quickly, on average by about 0.4 degrees Fahrenheit every decade. At a depth of about 75 feet, the increase is about 0.2 degrees per decade, they say, enough to jeopardize species “unable to adapt evolutionarily or behaviorally.”

Over the last 137 years, the researchers say, the ice-free season has lengthened by more than two weeks, primarily because ice forms later in the year. The database, including data on chlorophyll that the family started collecting in 1979, suggest that the “growing season” for plankton and algae has lengthened in the lake. Chlorophyll levels have tripled since measurement began, the researchers said.

Ordinarily, the researchers said in their report, this increased plant growth would be accompanied by decreases in water clarity, but that is not what the data show at Lake Baikal. This finding, they said, “highlights the importance of establishing monitoring for ‘early warming’ before a need for monitoring may be perceived visually.”