evidence: Despite this clear upward trend, global mean sea level does not increase in a perfectly linear fashion. It exhibits temporary ups and downs due to various natural phenomena and seasonal variations. One that is very noticeable is an annual cycle that results from changes that happen in our climate over the course of a year. In each hemisphere the oceans warm and expand in summer, and cool and contract in the winter. Sea levels in each hemisphere are higher in summer and early autumn, and lower in winter and early spring. In addition, there is an increase of water stored on land in the Northern Hemisphere winter and thus less in the ocean, leading to a lower global average sea level at this time of year. While these annual changes happen at different times of the year in each hemisphere, they average together to a noticeable shift in globally averaged sea level over the course of the year. In the global average, this shift is around 1 inch (2 cm) on average, although the annual cycle can be much larger in local sea levels.