According to alarmists like Al Gore, one of the biggest threats of “global warming” is the rise it will cause in sea level. After all, they say, as the earth gets warmer, more of its ice will melt, and the seas will rise. If this happens to any great extent, sea levels could rise several feet. In fact, NASA’s chief Chicken Little, James Hansen, has claimed that “global warming” could cause the sea levels to rise as much as 20 feet!.1 As “proof” that “global warming” is already causing sea level rises, these alarmists note that sea levels have risen by about 20 centimeters in the past 100 years. 2
Now of course 20 centimeters (about eight inches) is a FAR CRY from 20 feet, but global warming alarmists assure us that the rise we have seen so far is definitely the result of global warming, and as global warming accelerates, sea level rise will accelerate as well. Of course, as is usually the case with global warming alarmists, what they say is squarely contradicted by the data.
S. J. Holgate has compiled a century-long record of sea level changes by examining a network of 177 tide gauges throughout the world. 3 Here is what he finds:
Extending the sea level record back over the entire century suggests that the high variability in the rates of sea level change observed over the past 20 years were not particularly unusual. The rate of sea level change was found to be larger in the early part of last century (2.03 ± 0.35 mm/yr 1904–1953), in comparison with the latter part (1.45 ± 0.34 mm/yr 1954–2003). The highest decadal rate of rise occurred in the decade centered on 1980 (5.31 mm/yr) with the lowest rate of rise occurring in the decade centered on 1964 (−1.49 mm/yr). Over the entire century the mean rate of change was 1.74 ± 0.16 mm/yr.
So what does this mean? Well, a negative rise indicates that the sea level actually decreased. Thus, in 1964 (as well as 1975, 1984, and 1999), the sea level actually fell. Also, note that the fastest rise in sea levels occurred 105-56 years ago. While the sea still rose a bit between 1954 and 2003, it was at a smaller rate of increase than in the early part of the 20th century. Thus, the rate of sea level rise is decreasing.
Now since the alarmists tell us that the past few decades are the ones that have seen the most “global warming, ” if global warming is causing the sea level to rise, it should have been rising fastest during the past few decades. Instead, it is rising more slowly now than it was 100 years ago! This tells us that whatever is causing the small amount of sea level rise we have been seeing over the past century, it is definitely not global warming.
Also, note the most important statement made by the authors. What has been observed over the past 20 years is not unusual. How can they make such a statement? Well, if you look at graph of the rate of sea level change versus year, you will see that the WIGGLES in the graph are MUCH LARGER than the trend in the graph. What I mean is that while the rate of sea level increase decreased over the past century, the decrease was small compared to the random up-and-down motion of the graph. Thus, any long-term trend is very hard to see because of the short-term variations. If the long-term trend is small compared to the short-term variations, this tells us that nothing unusual is going on.
The conclusion that nothing unusual is going on seems to be what most most responsible climate scientists have come to. What we see happening in climate now is not at all unusual compared to what has happened in earth’s past. The only thing unusual about the past 20 years is how the alarmists have been able to frighten unsuspecting people into believing that “global warming” will lead to a catastrophe.
2. Douglas, Bruce C., “Global Sea Rise: A Redetermination,” Surveys in Geophysics 18:279–292, 1997
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3. Holgate, S. J., “On the decadal rates of sea level change during the twentieth century, ” Geophysical Research Letters, 34, L01602, 2007
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