> Because while the winter maximum used to increase (5y average) in the last 40 years, the summer maximum decreased (5y average) over the same period. March e

> Because while the winter maximum used to increase (5y average) in the last 40 years, the summer maximum decreased (5y average) over the same period. March extent has neither decreased, nor increased. It hasn't been decreasing at all. The largest extent in march has occurred in the years 2008, 2013, 2014 and 2015.