Global sea levels have always varied in response to changes in climate. During the last ice age - about 10 000 years ago - a vast amount of water was trapped on land as ice, and sea levels were about 100 metres lower than today. As the ice melted, sea levels began to rise - a process that is still going on.
"The further into the 20th century, the faster the rise in sea level: this acceleration has continued into the 21st century, though there is some indication that it has dropped a little in the last 6-7 years" says SMHI oceanographer Thomas Hammarklint.
Reports from sea level stations throughout the world indicate rising sea levels, and this is confirmed by satellite observations. This accelerated rise in sea level is partly due to the expansion of the seas as they warm up (so-called thermal expansion) and partly due to the increased flow of water into the ocean from land-based ice such as glaciers and the Greenland and Antarctic ice sheets. This is caused by global warming.
"Continuous sea level measurements are important for our understanding of global warming. The Swedish measurement series are extremely useful, as SMHI has measured sea level around the Swedish coast since 1886" continues Thomas.
Increase of 3 mm/year since 1980
Since 1886, sea level around the Swedish coast has risen by almost 20 cm - equivalent to an annual rise of 1.5 mm. "Over the last 30 years, we have seen the rate of increase accelerate. Regression analysis shows the annual rise in sea level over the last 30 years to be 3 mm/year (1980-2009). This new rate is double the rate observed over the period 1886-2009" says oceanographer Thomas Hammarklint.
Land-rise reduces the impact in the north
In Scandinavia, the increase in sea level is not so apparent in the north where the land is still rising at about 1 cm/year in response to the removal of the heavy ice sheets from 10 000 years ago. In the south however, land rise is much slower than in the north, and the increasing sea levels are more clearly noticeable.