The chart above gives us information about what percentage of several north American lakes’ surface was frozen during two 20-year periods, from 1973 to 1992 as well as 1992 until 2012.
Overall, in 1973-1992 year more territory of all of the lakes was covered in ice. In the first two decades lake erie had the most ice-covered surface out of them all reaching 30%, in the next twenty years frame the percentage just dropped below 30.
We must take notice, numbers dipped sharpest in case of Lake Superior. In the years of 1973-1992 a little over 25% of superior was frozen, while in 1992-2012 period number fell to nearly 14%.
On the other hand, during both 20-year periods lake Ontario was the least ice-covered among all fime of them.