Epilimnetic temperatures from early 1980s through 2017 were analyzed for 12 Wisconsin (USA), German, and Finnish lakes. Seasonal temperature metrics exhibited large interannual variability with trends differing among regions. In the Wisconsin lakes, only late summer and fall temperatures increased significantly. In the 2 northeastern German lakes, temperatures increased in all seasons (not all significantly). The 3 Finnish lakes exhibited large spring temperature increases influenced by earlier ice-out; summer and fall temperatures also increased except for Konnevesi (central Finland) in early summer and polar Kevojärvi in midsummer. Kevojärvi also exhibited no increase in maximum recorded temperatures. Earlier records from 4 lakes were analyzed to elucidate longer-term epilimnetic temperature patterns. For Lake Mendota (southern Wisconsin), spring and late fall temperatures have increased modestly but significantly since 1894; summer temperatures have also increased modestly because of higher frequency of warm temperatures in recent summers and not from new record high temperatures. Trout Lake (northern Wisconsin) exhibited warm temperatures in some summers during the 1930s–1940s, similar to warm temperatures in some recent summers. Air–water temperature relationships coupled with long-term regional air temperature data also indicated summer epilimnetic temperatures in the study lakes were likely as warm in the 1930s–1940s as in recent years. Lake data confirmed cooler epilimnetic temperatures occurred in many summers during the 1950s–1980s coincident with cooler air temperatures. Because epilimnetic temperatures have not increased monotonically since 1900, our study supports continued temperature monitoring in lakes with extensive historical data to better understand and predict future effects of climate change on lake ecosystems.

分析了1980年代初至2017年的Epilimnetic温度，其中包括12个威斯康星州（美国），德国和芬兰湖泊。季节温度指标表现出较大的年际变化，各地区之间的趋势也不同。在威斯康星州的湖泊中，只有夏末和秋季温度显着升高。在德国东北部的两个湖泊中，温度在所有季节都升高（并非都显着升高）。受早期冰冻影响，芬兰的3个湖泊的春季气温升高幅度较大。除了夏季初的Konnevesi（芬兰中部）和仲夏的极地Kevojärvi外，夏季和秋季的温度也有所升高。Kevojärvi的最高记录温度也没有升高。分析了来自4个湖泊的早期记录，以阐明长期的外层温度模式。对于门多塔湖（威斯康星州南部），自1894年以来，春季和秋季末温度略有上升，但显着增加。夏季温度也有所上升，这是因为最近夏季的温暖温度较高，而不是新的创纪录高温。鳟鱼湖（威斯康星州北部）在1930年代至1940年代的某些夏季表现出温暖的温度，类似于最近一些夏季的温暖温度。空气与水的温度关系以及长期的区域空气温度数据也表明，1930至1940年代，研究湖泊夏季的lim外温度可能与近年来一样温暖。湖泊数据证实，在1950年代至1980年代的许多夏天，较低的上层温度发生在气温较低的同时。自1900年以来，外延温度没有单调增加，