Sea level rise

Where we are today

Sea level continues to rise at an accelerated rate. Global mean sea level for 2018 was around 3.7 mm higher than in 2017 and the highest on record. Accelerated ice mass loss from the ice sheets is the main cause of the global mean sea-level acceleration.

Source: WMO Statement on the state of the global climate in 2018

Where we are heading

Sea levels are expected to continue to rise with accelerating speed. Levels depend on the effort we undertake to mitigate climate change and a complex interaction of global and local/regional factors. Uncertainties are high, especially after 2050, but can nevertheless help improve decisions on coastal development. Beyond 2100, sea level will continue to rise for centuries and will remain elevated for thousands of years.

Sea level does not rise uniformly. Observations show that sea level shows substantial regional variability. The regional differences are due to a range of local factors, such as wind, flows of freshwater and melting of ice.

Drivers for sea level rise

There are a number of global and regional factors that drive sea level rise. Some of these are still not well understood and scientists are increasingly understanding the complex interactions.

Global drivers for sea level rise are:

The melting of ice sheets and ice shelves, mainly on Greenland and Antarctica
The melting of glaciers
Ocean heating, leading to a thermal expansion of sea water
Changes in terrestrial reservoirs of groundwater and surface water

Regional and local drivers for sea level rise are:

Winds
Currents
River runoff
Local ice processes
The distribution of water mass between land, ice and ocean, triggering changes in Earth’s gravity field and rotation

What it means

Sea level rise reduces the land available for settlement and agriculture and poses direct risk to lives and infrastructure. Currently around 370 million people are living in areas below 5 meters of elevation. Many of these would be directly affected. This number is likely to grow with increasing overall population and the ongoing move from rural areas to cities, many of which are at the coast.