Historical trends in lake and river ice cover in the Northern Hemisphere

Freeze and breakup dates of ice on Lakes and rivers provide consistent evid ence of Later freezing and earlier breakup around the Northern Hemisphere f rom 1846 to 1995, Over these 150 years, changes in freeze dates averaged 5. 8 days per 100 years Later, and changes in breakup dates averaged 6.5 days per 100 years earlier; these translate to increasing air temperatures of ab out 1.2 degrees C per 100 years. Interannual variability in both freeze and breakup dates has increased since 1950. A few Longer time series reveal re duced ice cover (a warming trend) beginning as early as the 16th century, w ith increasing rates of change after about 1850.