Although it may not be immediately obvious when we visit the beach, sea-level rise is affecting coastlines all over the world. For low-lying countries such as the Netherlands, sea-level rise and tidal surges are a constant threat. Our oceans are rising as a consequence of climate change. As the temperature of seawater increases it expands and the ice melting from ice sheets and glaciers adds more water to the global ocean. We know this because satellites high above our heads measure the temperature of the sea surface and of our changing ice.
While the global averaged trend is towards rising levels, there are many regional differences so that in some places it is rising and in other places it is falling. Satellites carrying altimeter instruments systematically measure the height of the sea surface so that sea-level rise can be closely monitored. Altimetry measurements over the last 25 years show that on average sea-level is rising about 3 mm a year and this rise is accelerating.