NASA GISS: Science Briefs: Sea Level Rise, After the Ice Melted and Todayhttp://www.giss.nasa.gov/research/briefs/gornitz_09/NASA released reports on global sea rise.:
It stood 4-6 meters above the present during the last interglacial period, 125,000 years ago, but was 120 m lower at the peak of the last ice age, around 20,000 years ago.
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By the mid-Holocene period, 6000-5000 years ago, glacial melting had essentially ceased, while ongoing adjustments of Earth's lithosphere due to removal of the ice sheets gradually decreased over time. Thus, sea level continued to drop in formerly glaciated regions and rise in areas peripheral to the former ice sheets. At many low-latitude ocean islands and coastal sites distant from the effects of glaciation, sea level stood several meters higher than present during the mid-Holocene and has been falling ever since. This phenomenon is due to lithospheric responses to changes in ice and water loading. Water is "siphoned" away from the central equatorial ocean basins into depressed areas peripheral to long-gone ice sheets. Loading by meltwater that has been added to the oceans also depresses far-field continental shelves, tilting the shoreline upward and thus lowering local sea level. Over the past few thousand years, the rate of sea level rise remained fairly low, probably not exceeding a few tenths of a millimeter per year.
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Twentieth century sea level trends, however, are substantially higher that those of the last few thousand years. The current phase of accelerated sea level rise appears to have begun in the mid/late 19th century to early 20th century, based on coastal sediments from a number of localities. Twentieth century global sea level, as determined from tide gauges in coastal harbors, has been increasing by 1.7-1.8 mm/yr, apparently related to the recent climatic warming trend. Most of this rise comes from warming of the world's oceans and melting of mountain glaciers, which have receded dramatically in many places especially during the last few decades. Since 1993, an even higher sea level trend of about 2.8 mm/yr has been measured from the TOPEX/POSEIDON satellite altimeter. Analysis of longer tide-gauge records (1870-2004) also suggests a possible late 20th century acceleration in global sea level.
Recent observations of Greenland and the West Antarctic Ice Sheet raise concerns for the future. Satellites detect a thinning of parts of the Greenland Ice Sheet at lower elevations, and glaciers are disgorging ice into the ocean more rapidly, adding 0.23 to 0.57 mm/yr to the sea within the last decade. The West Antarctic Ice Sheet is also showing some signs of thinning. Either ice sheet, if melted completely, contains enough ice to raise sea level by 5-7 m. A global temperature rise of 2-5°C might destabilize Greenland irreversibly. Such a temperature rise lies within the range of several future climate projections for the 21st century. However, any significant meltdown would take many centuries. Furthermore, even with possible future accelerated discharge from the West Antarctic Ice Sheet,
it highly unlikely that annual rates of sea level rise would exceed those of the major post-glacial meltwater pulses.