Abstract A simulation model for ice and snow covers is applied to dimictic and polymictic lakes of the temperate zone to project the effects of possible climate warming on ice and snow covers. The winter cover model is associated with a deterministic, one-dimensional water temperature model. The lake parameters required as model input are surface area ( A S), maximum depth ( H max), summer and Secchi depth as a measure of radiation attenuation and trophic state. The model is driven by daily weather data. The model has been validated with extensive data. Standard errors between simulated and measured values are 0.12 m for ice thicknesses, 0.07 m for snow covers and less than 6 days for ice formation dates. The model is applied to simulate effects of projected climate change on winter ice and snow covers on different types of lakes in Minnesota. Lake depth and latitude are shown to have the strongest influence on freeze-over dates. Lake morphometry causes variations of up to 6 days in the mean value of ice-in dates. The trophic state and shape of a lake have little effect on ice-out date, but latitude is important. The projected climate change due to a doubling of atmospheric carbon dioxide (2 × CO 2) is obtained from the output of the Canadian Climate Center Global Circulation Model (CCC GCM) and the Goddard Institute of Space Studies at Columbia University (GISS GCM). The 2 × CO 2 climate delays the ice formation by as much as 20 days, reduces maximum ice and snow thicknesses by 50%, and shortens the ice cover period by up to 60 days. These changes would eliminate fish winterkill in most shallow lakes, but would endanger snowmobiles and ice fishermen. To illustrate the effect of projected climate change on winter ice/snow cover characteristics, separate graphs are presented for values simulated with inputs of past climate conditions (1961–1979) and with a projected 2 × CO 2 climate scenario. Independent variables used on these plots are a lake geometry ratio A S 0.25 H max and Secchi depth. The lake geometry ratio measures the susceptibility of a lake to stratification.