Lakes as sentinels of climate change

Abstract

While there is a general sense that lakes can act as sentinels of climate change, their efficacy has not been thoroughly analyzed. We identified the key response variables within a lake that act as indicators of the effects of climate change on both the lake and the catchment. These variables reflect a wide range of physical, chemical, and biological responses to climate. However, the efficacy of the different indicators is affected by regional response to climate change, characteristics of the catchment, and lake mixing regimes. Thus, particular indicators or combinations of indicators are more effective for different lake types and geographic regions. The extraction of climate signals can be further complicated by the influence of other environmental changes, such as eutrophication or acidification, and the equivalent reverse phenomena, in addition to other land-use influences. In many cases, however, confounding factors can be addressed through analytical tools such as detrending or filtering. Lakes are effective sentinels for climate change because they are sensitive to climate, respond rapidly to change, and integrate information about changes in the catchment.

Fig. 1

Long-term behavior of monthly mean near-surface temperatures since 1970 in January (T_Jan, A–D) and July (T_July, E–P) in various Northern Hemisphere lakes. (A) and (E) Lake Zürich (Switzerland); (B) and (F) Lake Constance (Germany, Switzerland, Austria); (C) and (G) Lake Washington (Washington); (D) and (H) Lake Tahoe (California, Nevada); (I) Greifensee (Switzerland); (J) Lake Vättern, Edeskvarva basin (Sweden); (K) Lake Mäleren, Görvaln basin (Sweden); (L) Stensjön (Sweden); (M) Müggelsee (Germany); (N) Lake Baikal (Russia); (O) Lake Champlain (Vermont); (P) Blue Chalk Lake (Canada). Monthly means were obtained by spline-interpolating measured temperatures at daily intervals and averaging the results. For each lake, the significance level of the Mann–Kendall test for the existence of a monotonic trend is indicated by one, two, or three asterisks (p < 0.1, p < 0.05, and p < 0.01, respectively) or a dash (no monotonic trend at the p < 0.1 level). The mean rate of change of T_Jan or T_July is also given, and the long-term linear trend is illustrated.