The article states:
For example, the study found that from 1443 to 1683, Lake Suwa's annual freeze date was moving almost imperceptibly to later in the year -- at a rate of 0.19 days per decade. From the start of the Industrial Revolution, however, that trend grew 24 times faster, pushing the lake's "ice on" date back 4.6 days per decade. ...
"Although there are local factors that are influencing both systems," says Sharma, "climate changes associated with increasing carbon dioxide emissions and air temperatures are important, perhaps overarching factors explaining the trends."
In recent years, she notes, both waters have exhibited more extreme ice dates corresponding with increased warming. For Lake Suwa, that means more years where full ice cover never occurs. Before the Industrial Revolution, Lake Suwa froze over 99 percent of the time, but beginning more recently, it does so only half the time. ...
"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," says Sharma -- with consequences for ecology, culture and economy.Lake Suwa sits high in the Japanese Alps. It is one of the few fresh water lakes in Japan, and, I believe, the largest. For that reason, at least when I was there as a missionary, there were several large manufacturing plants scattered around the lake operated by companies such as Seiko and Canon. The local economy was very dependent on electronics manufacturing. The lake not only provided water needed for their manufacturing processes, but was also a convenient place to discharge wastes, including hot water that had been used for cooling. (As an aside, those companies also funded what was the largest fireworks display in Japan at the time, set off over the lake, and some even on the surface of the lake--very awesome).
Pollution of the lake was a problem. One of the gentlemen I taught, while there, had been a tank driver in World War II. He said that during World War II, they could drive their tanks over the lake, the ice was so thick. At the time I was there (late 1980's), though, locals told us that the lake rarely had any ice at all. It also lacked fish and other wildlife around its edges. Suwa City had a large number of hotels and a very nice park along the lake shore, but they piped in bird sounds over loud speakers because there were no birds.
In short, the lake was polluted, which lowered its freezing point, and had hot water dumped into it. Ice cover was more complete and thicker as recently as World War II. In my mind, this raises serious questions regarding the conclusions of the climate researchers that the change in ice formation is due to atmospheric CO2.
Update (4/28/2016): An article and numerous comments at Watts Up With That regarding the research.