Greenhouse-gas emissions are the main cause of rising sea levels since 1970

The current rise of sea levels is the fastest in the past 3000 years. New research shows that humanity's influence on the climate is the main reason for rising sea levels since 1970. The sea levels are expected to keep rising in a warming climate. Primary author Dr Aimée Slangen of Utrecht University publishes about this in Nature Climate Change. The research was financed by the Netherlands Polar Programme.

The article in Nature Climate Change shows that the biggest part of the observed rise of sea levels since the end of the 20th century is caused by human influence on climates. The researchers came to this conclusion after they compared the globally measured average rise of sea levels to estimates made by climate models. Scientists already suspected that the emission of greenhouse gases by humans is responsible for the rising sea levels, but this research project definitively showcases it.

The article shows that the driving force behind sea-level change has changed from natural to human in the course of the 20th century. Right now, human action is the dominant cause of the observed changes and it will probably stay that way as long as greenhouse-gas emissions are not reduced.

Natural influence versus human influence

The sea levels are rising primarily due to water expansion as a result of increasing temperatures and melting ice. In the beginning of the 20th century, human influence on the climate (due to the emissions of greenhouse gases and aerosols) was very small; only 15 per cent. However, human actions explain most of the observed sea-level risings, almost 70 per cent, since 1970. Internal climate variability and natural factors such as volcanic eruptions do influence sea levels on an annual basis, but their influence on the 20th century as a whole is very small.

The delayed reactions of the glaciers and ice caps to global warming after the Little Ice Age (1300-1870) explains many of the observed sea-level changes that occurred before 1950 (almost 70 per cent), but not after 1970 (less than 10 per cent).

When all known influences, both human and natural, are taken into account, the climate models explain about three quarters of the observed changes since 1900 and almost 90 per cent since 1970. These differences can be caused by the models themselves (such as underestimating the ice-cap contribution) and by the observational data (lesser quality before 1970).