Published in Nature Climate Change: CSIRO researchers have confirmed that the majority (70%) of the observed sea level rise since the late 20th century is due to human influence.
Previous studies have already examined the influence of two major drivers of sea level change - the expansion of oceans as they get warmer and the contribution of mass loss of melting glaciers.
But the CSIRO research has now also included other contributors of rising sea levels. Its major finding is that drivers of climate variability, such as El Niño, solar variability and volcanic activity, are secondary contributors to the rise in sea levels over the past century, which has been at a much faster rate than in previous millennia.
The researchers base this conclusion on a comparison of the observed global mean sea-level change to sea level estimates from models.
Over the 20th century as a whole, the impact of internal variability and natural drivers (such as volcanic eruptions) was found to have been small and could explain little of the observed sea-level trend.
The research also shows that the delayed response of the glaciers and ice sheets to the warmer temperatures after the Little Ice Age (1300 to around 1870 AD) contributed a lot to the observed sea-level change before 1950 (nearly 70%), but very little after 1970 (less than 10%).
By contrast, the combined influence of human forcing (greenhouse gases and aerosols) was small in the beginning of the century (only 15%), but after 1970 the majority of the observed sea-level rise can be attributed to human influence (nearly 70%), with an increasing percentage up to the present day.
Overall, the models were able to explain about three quarters of the observed rise since 1900 and almost all (almost 90%) of the rise since 1970. This, the scientists believe, could be the result both differences in the model estimates (for instance an underestimated ice sheet contribution) and in the lower quality sea level observations prior to the satellite record.