  The variation in the Arctic sea ice is dominated by the seasonal cycle with
little inter-annual correlation. Though the mean sea ice area has decreased
steadily in the period of satellite observations, a dramatic transition in the
dynamics was initiated with the record low September ice area in 2007. The
change is much more pronounced in the amplitude of the seasonal cycle than in
the annual mean ice area. The shape of the seasonal cycle is surprisingly
constant for the whole observational record despite the general decline. A
simple explanation, independent of the increased greenhouse warming, for the
shape of the seasonal cycle is offered. Thus the dramatic climate change in
arctic ice area is seen in the amplitude of the cycle and to a lesser extend
the annual mean and the summer ice extend. The reason why the climate change is
most pronounced in the amplitude is related to the rapid reduction in perennial
ice and thus a thinning of the ice. The analysis shows that a tipping point for
the arctic ice area was crossed in 2007.
