Figure 4.7. Trends in (a) freeze-up and (b) breakup dates observed at lakes in Canada over the period 1965 to 1995. Downward pointing arrows indicate a trend towards earlier dates; upward pointing arrows, a trend towards later dates. Open symbols indicate that the trend is not significant while solid symbols indicate that the trend is significant at the 90% confidence level (modified from Duguay et al., 2006).