Sea Level Rise
According to NASA global sea level rose about 20 cm in the last century. The rate in the last two decades, however, is nearly double that of the last century and accelerating slightly every year.
Sea Levels Rising
There are two principal causes of sea level rise. One is the melting of ice from ice sheets and glaciers. The other is the warming of seawater.
Satellite data from 1993 to the present day shows an increase of about 104mm in sea height to date. These data are shown in the chart.
You can find out more about the data - and an alternative set based partly on coastal tidal gauge data - here. You can also access NASA's sea level data from a link on the same page.
The Ice Sheets are Losing Mass
Antarctica is losing ice mass - i.e. melting - at an average rate of about 150 billion tons per year. The chart shows satellite data from 2002 to the present.
Greenland is losing about 270 billion tons per year. You can see the corresponding chart for Greenland here. On that page you can also get access to NASA ice sheet data.
Between them the Greenland and Antarctic ice sheets store about 2/3 of all the fresh water on Earth. Warming of these ice sheets is therefore making a major contribution to sea level rise.
April 2023: Miami and New Orleans face greater sea-level threat than already feared
Coastal cities in the southern USA, including Miami, Houston and New Orleans, are in even greater danger from sea-level rise than already feared, according to this article.
A paper referrenced in the article reports a dramatic surge in ocean levels of almost 5in (12.7cm) along the US south-eastern and Gulf of Mexico coastline since 2010.
February 2023: António Guterres warning
At a speech in New York on 9 Feb 2023 UN Secretary General António Guterres told the audience that rising seas are a serious threat requiring a coordinated global response at the highest levels. He said that with 900 million people at risk, sea level rise could drive “a mass exodus of entire populations on a biblical scale”. 900 million people represent over 10% of the world's population, and such an impact could threaten world peace.
You can find out more about his speech here.