Why are sea levels rising?

There are two big reasons why sea levels are rising.

The first big reason is that as water gets warmer its volume expands. You can try this at home. At room temperature, 1 litre of water weighs 1 kilogram. When this water is heated, its mass stays the same but its volume increases.

The second big reason is that ice sheets and glaciers around the world are melting, adding mass to the ocean. From around the start of the 21st century, melting ice has been the largest reason for sea level rise. Ice sheets in Antarctica presents our greatest challenge - did you know that if all the ice in Antarctica melted it would add around 58 metres in sea level height?!

But the ocean is always moving, how do we measure sea level rise?

The ocean surface is constantly moving, with waves, stormy weather, and tides. Scientists measure changes in sea level using lots of frequent measurements by hundreds of tide gauges around the world, some which have operated for more than 100 years. For over 30 years, satellites have also measured sea level from space, covering the wide expanses of ocean far from any tide gauge. These measurements are averaged to give local and global estimates of sea level trends, taking into account changing land height. Measurements tell us that on average, sea level is rising and at an increasing rate. Some places are rising faster than others, in some places sea level is falling, but most locations are currently seeing around 4mm/year in sea level rise.

What can be done?

The most important thing to do about sea level rise is to slow it down by stopping burning fossil fuels. However, even if global warming stopped tomorrow, sea levels would continue to rise, likely for centuries, because of the heat that is already in the oceans. For this reason, we need to prepare everyone connected to the coast for change and improve our knowledge of how sea level rise will affect different places.