December 4, 2006

Decelerating the Sea Level Rise Scare

One of the basic, and often never challenged claims of the global warming advocates is that sea level is rising, and thanks to global warming, the rise in sea level is accelerating at an alarming pace. Many popular presentations of the global warming issue (e.g., Gore’s film) show images of low-lying nations that are seeing their islands erode away thanks to the rising seas. Throw in a few locals dressed in native clothing who looked distraught over the situation, blame the industrialized nations (and obviously the United States), and another pillar of the global warming story is reinforced.

If one simply took the time to examine the Intergovernmental Panel on Climate Change 2001 report, they may be absolutely stunned to read “No significant acceleration in the rate of sea level rise during the 20th century has been detected.” Although since the publication of the IPCC 2001 report, a few studies have been published which report to have found evidence of sea level rise acceleration. However, the jury is still way out on this issue.

A recent article in the Journal of Coastal Research by Curtis Larsen and Inga Clark of the U.S. Geological Survey in Reston, Virginia provides an interesting perspective on sea level rise. They begin their article noting “Current studies of accelerated rates of sea-level rise have their roots in the documented increase in atmospheric CO2 during the latter half of the 20th century.” There is certainly no debate here – sea level rise issue and elevated levels of atmospheric carbon dioxide (CO2) are cornerstones of the popular global warming presentation. Larsen and Clark mention “An influential collection of papers” that “called attention to climate-related sea-level rise and future flooding of coastal lowlands in response to increases in ‘‘greenhouse’’ gases and an apparent exponential increase in CO2 and global temperature.” The papers we could cite here are in the hundreds particularly if we left the scientific journals and examined more popular magazines (e.g., Time, Newsweek, National Geographic). As noted by Larsen and Clark, these papers present a view that “sea-level rise accelerates in tandem with an exponential increase in CO2 and atmospheric temperature. This simple concept has been used to argue that the rate of sea-level rise was low over the past 6000 years, began to increase during the 19th century, and will continue to increase during the next century.”

The two scientists discuss the methods of estimating relative sea level (RSL) and note that “The most reliable records of Holocene sea-level rise are derived from radiocarbon-dated organics from basal peat deposits along stable or apparently subsiding coasts.” Such ideal locations are a bit hard to find and introduce error into estimates of relative sea level over thousands of years. They note that “Significant basal peat records of RSL rise for the past 6000 years are available for Chesapeake Bay, Long Island Sound, CapeCod Bay, and Delaware Bay” among other sites in the United States. However, they note up-front with respect to hard measurements of sea level in the United States, “Unfortunately, US tide gauge records are insufficiently long to identify any acceleration in rate of sea-level rise from a background state.” It looks like claims of accelerated sea-level rise are in for some criticism?

Figure 1 below shows that sea level has undoubtedly been rising for 6,000 years, and the rates seem rather monotonic. Quotes from throughout the Larsen and Clark paper are priceless. They state “the earlier part of the Dennis Creek reconstruction shows general agreement with the long-term rate of RSL rise at 2.0 mm/y until about AD 1750. The RSL trend then rapidly rises until the early 20th century, when it slows and tends to parallel the historic tide gauge record of 2.6 mm/y.” The Dennis Creek reconstruction had accelerated sea-level rise alright, but it occurred from AD 1750 to the early 1900s!

Figure 1. Relative long-term sea-level trends for Delaware Bay; Clinton, Connecticut; Barnstable, Massachusetts; and Chesapeake Bay (from Larsen and Clark, 2006).

Elsewhere they note “the Newport, Rhode Island, tide gauge provides a 0.9-mm/y rate as well. The residual sea-level trend shows no apparent agreement with that of atmospheric CO2.” When a “Guilford marsh reconstruction” is “detrended and compared to the CO2 record of the same period, there is no indication of an exponential increase in the rate of sea-level rise.” They present many other sites that simply do not show the expected accelerated rise in sea level over the past 100 or so years when the greenhouse gas buildup increased.

In conclusion, Larsen and Clark note that “there is no discernible divergence in the rate of sea-level rise over the past two centuries to suggest a connection with the documented increase in atmospheric CO2 concentration.” This conclusion is reinforced with the comment that over 1,000s of years “the rate of sea-level rise has been linear over this time period and shows no indication of the pronounced mid-20th-century increase” with any increase in global temperature. And for even more interesting evidence, they write “Worthy of note is the apparent opposite direction of the sea-level trends for the past few decades, which show rise in North America and fall in the Baltic, thus arguing against recent acceleration in sea-level rise.” They wrap up their interesting article stating “One of the conclusions of our study is that there has been a tendency to splice together rates of sea-level rise with little regard to the suitability of scale and to derive curves that show steadily increasing rates of sea-level rise.”

Enough said.


Larsen, C.E. and I. Clark. 2006. A search for scale in sea-level studies. Journal of Coastal Research, 22(4) ,788–800.

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