諏訪湖
As a shallow lake, Lake Suwa is highly sensitive to climactic variation. Recent studies have shown that Suwa's ice-free years correlate to increasing atmospheric CO2 levels. Research on ice breakup at Suwa and at the mouth of the Torne River in Finland suggest that climate change is driving the changes in seasonal ice cover. As a result, it is expected that Lake Suwa will remain ice-free for almost the entirety of the 21st century's winters.