Sea Level Variations - Measuring present-day changes

Sea levels can vary if the volume of the oceans increases or if changes of the temperature of the oceans causes thermal expansion. Both of these would occur as a consequence of global warming. Accurate knowledge of variations in sea level is essential for our society.

How do we measure sea level? Relative sea level (the height of the water relative to the land) can be measured using tide gauges but it then becomes critical to know whether the land itself is moving before knowing whether the absolute height of the oceans is changing. Satellite altimetry measures the distance between an Earth-orbiting satellite and the surface of the ocean. Knowing accurately the position of the satellite we can know the height of the ocean relative to the centre of the Earth.

Are sea levels changing? Yes, they are. There is strong scientific evidence that sea levels are rising and it has been suggested that it may be accelerating (Church and White, GRL, 2006). But improving the accuracy with which we can measure changes in sea level - and hence understand better the processes of climate change - remains an ongoing task.