An 80 Foot Sea Level Rise!!??
Here is a graphic that will make you stand up and take notice–especially if you have relatives who live in New York City. This image appeared in Vanity Fair magazine in May 2006 and shows how much of New York City would be under water if all of the ice on Greenland and the Antarctic were to melt causing sea levels to rise 80 feet. 80 feet! Where did they get that number? What a scare tactic. Not even Al Gore uses a number that high. Certainly the IPCC doesn’t.
What does the IPCC Summary released in February have to say about sea level rise? This is the published chart from page 11 of the Summary. 
The numbers are for each of six different CO2 emissions scenarios and are in meters. Converting to inches gives a range of 7 to 23 inches by the end of the 21st century with the mean values between 8 and 18 inches. Those numbers don’t exactly portray an 80 foot catastrophe. And the IPCC does give this caveat to their forecast:
Models used to date do not include uncertainties in climate-carbon cycle feedback nor do they include the full effects of changes in ice sheet flow….the projections include a contribution due to increased ice flow from Greenland and Antarctica at the rates observed for 1993-2003, but these flow rates could increase or decrease in the future.
They also state on page 13 that if temperatures warm in excess of 3.4 to 8.3 degrees Fahrenheit and continue at that value for a MILLENNIA, the result would be an elimination of the Greenland ice sheet resulting in a sea level rise of about 20 feet. In other words, a 20 foot sea level rise in 1,000 years is possible from the complete melting of the Greenland ice sheet IF the highly uncertain computer model forecasts of future temperature rises and ice flow are correct. The ice flow rates could actually “decrease in the future”. Part of the projected sea level rise is due to the expansion of water as it warms and this is factored into the IPCC forecasts.
What about the Antarctic ice sheet? Is it melting away as many news stories such as this one titled “Antarctic Glaciers going, going, gone” have implied? Here is a quote from the IPCC on page 13:
Current global model studies project that the Antarctic ice sheet will remain too cold for widespread surface melting and is expected to gain in mass due to increased snowfall.
Indeed, the average temperature on the Antarctic continent is 56 degrees below zero Fahrenheit. When you look closely at the news stories such as the one above, you find that the ice melt has been on the West Antarctic Ice Sheet on the Antarctic Peninsula, not on the main continent. There is some disagreement as to the cause of this ice melt, but even Real Climate (a web site strongly supportive of global warming) states:
The retreat of these glaciers in itself will have a negligible effect on sea level, since most of the ice that has retreated was in the water already.
Since there are no current global warming scenarios which produce a temperature rise of the magnitude needed to melt the Antarctic ice sheet, the forecast of an 80 foot sea level rise clearly seems to be another example of the many exaggerations made about this subject. It seems to me a little like the outrageous comment of Sir David King, the United Kingdom’s Chief Scientist who says “Antarctica is likely to be the world’s only habitable continent by the end of this century if global warming goes unchecked”.
A 20 foot rise in 1,000 years is a concern, but there are so many admitted uncertainties in that forecast, even it can’t possibly be portrayed as a sure thing.
Posted: March 19th, 2007 under All Blog Posts, Craig James.