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Will Global Warming Flood Coastal United States?

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Two new studies are predicting accelerated sea-level rises on the East and West coasts of the United States, primarily due to global warming. Major media outlets—and in some ways the studies themselves—have painted a distorted picture of past, current, and future sea levels. In fact, the studies actually conflict with each other, a crucial fact that has gone unreported in news reports that have mentioned both of the studies.
One study, henceforth referred to as the “East Coast study,” was published in the journal Nature Climate Change and shows a “recent acceleration” of sea-level rise on the East Coast from North Carolina to Massachusetts. According to the Associated Press, “By 2100, scientists and computer models estimate that sea levels globally could rise as much as 3.3 feet,” and this study predicts that the East Coast could see “8 to 11 inches more” than this, hence “putting one of the world’s most costly coasts in danger of flooding….”
The other study, herein dubbed the “West Coast study,” was published by the National Research Council and publicized with a Los Angeles Times headline that reads “California sea levels to rise 5-plus feet this century, study says.”
Sensation versus information
First, a lesson in journalistic sensationalism: The AP’s claim about “scientists and computer models” predicting global sea-level rises by 2100 of “as much as 3.3 feet” could just as well have been worded “as little as 7 inches.” This 3.3 feet figure is not from the study that is the subject of the AP article, and by citing the authority of scientists and computer models, the AP gives the distinct impression that this result is universal. The reality, however, is that a 2011 paper in the Journal of Coastal Research explains that such projections run as low as 7 inches. An honest way to report this would have been to provide a range of estimates (such as 7 inches to 3.3 feet), not a single cherry-picked example.
The Los Angeles Times headline about the West Coast study—“California sea levels to rise 5-plus feet this century”—is even more misleading because the language is unequivocal. In truth, the study predicts a sea-level rise of 16.5 to 66 inches over this period. In the body of the article, the LA Times reporter walks back the headline and applies the qualifier “as much as” to the 5-plus-feet figure, but he fails to provide even a hint that this is the upper bound of a prediction that extends to as low as one fourth of this.
Reuters took the hyperbole a leap further by claiming that the East Coast study shows “sea levels from Cape Hatteras to Cape Cod are rising at a faster pace than anywhere on Earth.” This assertion appears to be completely fabricated. The study compares global average sea-level accelerations to those on the coastlines of the continental U.S. and southernmost portion of Canada. It says nothing about any other specific locations, and an email to one of the study’s authors confirms that the study “does not make comparisons ‘to anywhere on earth’.”
Methods versus results
Second, a lesson in scientific conflict: The East Coast study found that the Northeast is a “hotspot” of sea-level acceleration, and the authors extrapolated recent historical data to calculate that sea levels in New York City will rise faster than the global average. However, in contrast, the study found that on the West Coast, all sea-level accelerations are either zero or negative (see Figure 2 and Supplementary Figure S3).
Yet, the West Coast study extrapolated “recent data into the future” to calculate that California sea levels will rise faster than the global average. In other words, if the scientists who performed the West Coast study used the same logic, data, and methods as used in the East Coast study, they would have projected that California sea levels will rise the same or less than the global average. Instead, they predicted the opposite.
As detailed below, the East Coast study contains two projections, one of which predicts that sea levels in New York City will rise a total of 15 to 18 inches over the 21st century. Again, the West Coast study projects that sea levels in California will rise 15 to 66 inches over the same period. If the studies’ projections were consistent with each other, there is no way that the cold spot of California could rise dramatically faster than the hotspot of New York City. This inconsistency reveals how the results of such projections are dependent upon the methods that scientists choose to employ.
Predictions versus history
Third, a lesson in forecasting: During the 20th century, the average global sea level rose by about 7 inches, and if this trend continues, sea level obviously will rise by another 7 inches in the 21st century. Some scientists, however, are predicting multiplicative increases in this rate. The problem with these predictions is that such increases have never been observed. As the West Coast study states, “Increases of 3–4 times the current rate would be required to realize scenarios of 1 m [3.3 feet] sea-level rise by 2100. Such an acceleration has not yet been detected.”
Projections of future sea levels are often based upon computer models, and the results of such models are frequently cited in the press without any qualifications about their uncertainty. However, as explained in the academic text Flood Geomorphology:
[T]rue science is concerned with understanding nature no matter what the methodology. In our view, if the wrong equations are programmed because of inadequate understanding of the system, then what the computer will produce, if believed by the analyst, will constitute the opposite of science.
The earth’s climate and oceans are extremely complex systems, and computer models predicting unprecedented accelerations in sea level are venturing into a realm of speculation that may prove to be the opposite of true science, regardless of the fact that it is scientists who program these models. Scientists often place appropriate disclaimers in their papers to convey this uncertainty, but these qualifiers rarely make it into the press coverage, leaving readers with the illusion that the results are more solid than they actually are.
Impressions versus realities
Fourth and most importantly, a lesson in political science: The official press release for the East Coast study states that “rates of sea level rise are increasing three-to-four times faster along portions of the U.S. Atlantic Coast than globally.” This language is easily misconstrued, and this is exactly what has occurred in many news reports. In the context of this study, the word “faster” refers to sea-level acceleration, not to sea-level rise. Yet, Reuters, for example, reported that “sea levels in this corridor were rising between three and four times faster than the global average.” This is simply not true.
This confusion between rise and acceleration has major implications because the global sea-level acceleration calculated in this study is so close to zero that even a tiny acceleration is large by comparison. The global acceleration (a sea-level rate difference of 0.59±0.26 mm per year over a 60-year period) equates to a grand total of about 0.4 to 1.0 inches of additional sea-level rise over 60 years.
In fact, global sea-level accelerations are so close to zero that they can be positive, zero, or negative depending upon the timeframe that scientists analyze. The above-mentioned 2011 paper in the Journal of Coastal Research reviews the results of numerous sea-level acceleration studies and concludes that there is “disagreement” over whether acceleration can “be detected.” Even the East Coast study, which is entitled “Hotspot of accelerated sea-level rise on the Atlantic coast of North America,” found that acceleration in this hotspot is “dependent on time-series length” and is “not significantly different from zero” for windows longer than 72 years.
The press release for the East Coast study mentions none of these critical facts, but it includes an unsupported assertion that isn’t even from the study, which is that “global sea level has been projected to rise roughly two-to-three feet or more by the end of the 21st century.” In conjunction with this, the press release adds another easily misconstrued statement:
During the 21st century, the increases in sea level rise rate that have already occurred in the hotspot will yield increases in sea level of 8 to 11.4 inches by 2100. This regional sea level increase would be in addition to components of global sea level rise.
Based upon these claims, one might conclude that the study predicts a sea-level rise in the Northeast of two-to-three feet plus 8 to 11 inches, which amounts to 32–46 inches. This is not the case, but one would never know it unless he or she took the time to scrutinize the study and a 25-page file of supplementary information. These documents show that the “components of global sea level rise” mentioned in the press release are not all components but some components. This means that one cannot add together the sea-level rise figures provided in the press release without double-counting some of the projected rise.
The press release could have cited another projection from the study that is very easily understood, which is that the total projected sea-level rise for New York City during the 21st century is 15 to 18 inches. This is less than half of what could be construed from the press release. However, one can’t find this projection even by reading the entire study because it was relegated to the very last page of the supplementary information. Moreover, the description of this projection is separated by 16 pages from the actual numerical result, making it difficult to put the two together.
Along the same lines, the West Coast study’s press release states that “San Francisco International Airport could flood with as little as 40 [16 inches] centimeters of sea-level rise, a value that could be reached in several decades.” What the press release fails to mention is that sea levels in San Francisco actually declined by 6 inches between 1992 and 2010.
Public versus private
Finally, a lesson in double standards. The East Coast study concludes with a statement that the “authors declare no competing financial interests.” The journal that published this study defines such interests as “those of a financial nature that” could potentially influence “the objectivity, integrity or perceived value of a publication.” Yet, the authors of East Coast study are employed by the U.S. Geological Survey, which is a federal agency funded by tax dollars. This could certainly be described as a competing financial interest given that federal government stands to reap trillions of dollars through global warming legislation.
Tellingly, Obama administration Treasury Department documents obtained under the Freedom of Information Act describe “emissions allowances under a cap and trade system” as “valuable assets” that are “analogous to revenue under an equivalent tax policy.” These documents specify that such legislation “could generate federal receipts” ranging from $100 to $300 billion every year.
If the scientists who conducted these studies worked for an oil company, the academic community would require them to declare this as a competing interest, and the press would mention it in every story that cited the study. Why should the standard be any different for scientists funded by governments?
Five lessons but no answer
So, will global warming flood the coasts of the United States? Despite what many media outlets and some scientists would lead us to believe, no one really knows. What we do know, however, is that a number of previous claims that global warming will cause flooding, starvation, and extreme weather have thus far proven unfounded.

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