Al Gore's documentary and associated book, A Inconvenient Truth, has been the subject of intense controversy and has stood up quite well to the attacks. But, nothing is perfect and here's one example discussed this week in the Global Warming Debate.
From the book (page 196): "If Greenland melted or broke up and slipped into the sea--or if half of Greenland and half of Antarctica melted or broke up and slipped into the sea, sea levels worldwide would increase by between 18 and 20 feet." This is a true statement and if it happened the World Trade Center Memorial would be under water.
The assertion, however, begs the question of (1) how likely is a sea-level rise of 18 to 20 feet and (2) how likely would such a sea level rise result from the melting of the ice sheets in Greenland or Antarctica? The Intergovernmental Panel on Climate Change (IPCC) has the answer buried in its reports.
Sea-level rise (SLR) is forecast to increase by about one-half foot every 100 years. In other words, sea level is expected to rise by 20 feet in the year 6000. What are the most likely sources of SLR?
This graphic is a little more difficult to explain since there are different measurements from two periods (Blue=1961-2003 and Brown=1993-2003). The important point to notice is that for either period, thermal expansion and glacier melt are the two most important sources of SLR. The melting of Greenland and Antarctica, given the error bars, provides almost a zero contribution.
This is not to say that we should not be concerned about the Greenland ice sheet or that there might not be a tipping point where the rate of melting gets accelerated. It's just that it's pretty far off in the future.
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