You're as cold as ice

In its 2007 report, the IPCC predicted a sea level rise of 28 to 43 centimeters (about 11 to 17 inches) by the end of the century. The figure was that low because the group included only expansion via heating in calculating the rise, excluding the effects of ice sheet and glacial melt on the grounds that their dynamics were not well enough understood to make good estimates.

There was a fair amount of criticism of that decision, which in fairness was undertaken to create a very scientifically conservative report, the better, it was thought, to convince doubters since the conservative findings were dire enough.

Be that as it may, it still seems that the more we look, the more the critics are, you'll pardon the expressions, on solid ground and the IPCC report on thin ice.

For one thing, it was known almost a year ago that the Antarctic Peninsula was experiencing dramatic warming and its glaciers were accelerating. But by January, it seemed clear the effects were not limited to that one area. The Washington Post reported that

[c]limatic changes appear to be destabilizing vast ice sheets of western Antarctica that had previously seemed relatively protected from global warming, researchers reported yesterday, raising the prospect of faster sea-level rise than current estimates. ...

"Without doubt, Antarctica as a whole is now losing ice yearly, and each year it's losing more," said Eric Rignot, lead author of a paper published online in the journal Nature Geoscience.

The Antarctic ice sheet is shrinking despite land temperatures for the continent remaining essentially unchanged, except for the fast-warming peninsula.

The reason, Rignot said, is believed to be global warming, causing the warmer waters of the Antarctic Circumpolar Current to come closer to the land in some area and so melt the edges of glaciers underwater.

In all, snowfall and ice loss in East Antarctica have about equaled out over the past 10 years, leaving that part of the continent unchanged in terms of total ice. But in West Antarctica, the ice loss has increased by 59 percent over the past decade to about 132 billion metric tons a year, while the yearly loss along the peninsula has increased by 140 percent to 60 billion metric tons. ...

The new findings come as the Arctic is losing ice at a dramatic rate and glaciers are in retreat across the planet. ....

"The information from Antarctica is consistent with what we are seeing in all other areas with glaciers - a melting or retreat that is occurring faster than predicted," [Lonnie Thompson of Ohio State University told the American Geophysical Union recently]. "Glaciers, and especially the high-elevation tropical glaciers, are a real canary in the coal mine. They're telling us that major climatic changes are occurring."

The thing is, when you take into account what has been learned more recently and apply that knowledge to a successful computer model, you find that

[s]ea levels could rise by up to one-and-a-half metres by the end of this century, according to a new scientific analysis. ...

The new analysis comes from a UK/Finnish team which has built a computer model linking temperatures to sea levels for the last two millennia.

"For the past 2,000 years, the [global average] sea level was very stable, it only varied by about 20cm," said Svetlana Jevrejeva from the Proudman Oceanographic Laboratory (POL), near Liverpool, UK.

"But by the end of the century, we predict it will rise by between 0.8m and 1.5m."

That is anywhere from double to six times the increase predicted by the IPCC.

When I said "a successful model," I was referring to the fact that Jevrejeva said their model

is able to mimic accurately sea levels reliably observed by tide gauges over the last 300 years.

For earlier years, the best evidence comes from archaeology, where the sill heights on fish enclosures used by he Romans indicate there hasn't been any significant change in sea level since that time. Which makes the changes seen recently even more significant and a real break from the past.