Natural Hazards

, Volume 65, Issue 1, pp 991–997

Oscillations of sea level rise along the Atlantic coast of North America north of Cape Hatteras

Authors

Short Communication

DOI: 10.1007/s11069-012-0354-7

Cite this article as:
Parker, A. Nat Hazards (2013) 65: 991. doi:10.1007/s11069-012-0354-7

Abstract

It is shown in the short comment that the sea levels are oscillating about a longer-term trend and that the sea level rise (SLR) computed with time windows of 20, 30 or 60 years also oscillates, with the amplitude of these latter oscillations reducing as the time window increases. The use of only two values of the SLR distribution is misleading to infer conclusions about the accelerating behaviour. In particular, the comparison of the 30-year SLR 1950–1979 with the 30-year SLR 1980–2009 for the tide gauges along the Atlantic coast of North America north of Cape Hatteras to infer an accelerating behaviour is particularly wrong because the 30-year time window is a too short interval to appreciate the longer-term sea level trend cleared of the multi-decadal oscillations, and the two values from the SLR distribution are computed, respectively, at the times of a valley and a peak for the 60-year Atlantic Ocean multi-decadal oscillation. By using a 60-year time window or all the data since opening when more than 60 years of recording are available and by analysing the SLR time history, the only conclusion that can be inferred from the analysis of the tide gauges along the North American Atlantic coast is that the sea levels are oscillating without too much of a positive acceleration along their longer-term trend.

Keywords

Sea level riseSea level accelerationDecadal and multi-decadal oscillationsTide gaugesAtlantic OceanNorth America

1 The tide gauges of the Atlantic coast of the United States

Sallenger et al. (2012) use in their analysis a short time interval of just 30 years to compute the sea level rise (SLR) to analyse the tide gauges along the North American Atlantic coast north of Cape Hatteras. Because there is a relevant 60-year cycle in the North Atlantic records, the 30-year choice is the worst that can be chosen because it is half the 60-year cycle. Fitting the last 30 years, the real SLR trend is overestimated, and fitting the previous 30 years, the real SLR trend is underestimated. The comparison of these two SLRs is not a proof of the existence of hot spots in the positively accelerating seas as claimed by the authors but only the evidence that the authors apparently do not know of the multi-decadal oscillations in the Atlantic.

Even if Sallenger et al. (2012) apparently do not, somebody else at NOAA knows that the sea levels are oscillating, with the multi-decadal oscillations up to the 60 years requesting proper consideration to infer trends from recorded data. The “Executive Summary” of the report NOAA (2009) says: “…50–60 years of data are required to obtain a trend with a 95 % confidence interval of +/− 0.5 mm/yr. This dependence on record length is caused by the inter-annual variability in the observations. A series of 50-year segments were used to obtain linear MSL trends for the stations with over 80 years of data. None of the stations showed consistently increasing or decreasing 50-year MSL trends, although there was statistically significant multi-decadal variability on the U.S. east coast with higher rates in the 1930s, 1940s and 1950s and lower rates in the 1960s and 1970s.”

Sallenger et al. (2012) compare the SLR 1950–1979 (30 years) with the SLR 1980–2009 (30 years) to find a section of the US east coast for which the SLR 1980–2009 is higher than the SLR 1950–1979. This difference of SLR is then used to claim the existence of positive sea level acceleration. The use of different time windows and the consideration of the SLR distribution in time provide a completely different conclusion.

As it is shown in Fig. 1 for the specific of The Battery, NY (but similar analysis can be carried out on all the other tide gauges of Table 1 producing the same results), 20-, 30- or 60-year SLR can be computed at any time but does not make too much sense to just focus on two numbers of a distribution of oscillating values.
https://static-content.springer.com/image/art%3A10.1007%2Fs11069-012-0354-7/MediaObjects/11069_2012_354_Fig1_HTML.gif
Fig. 1

Measured monthly averages (a), their deviations versus the linear trend (b) and the computed SLR obtained by linear fitting of the last 20, 30 and 60 years of data up to any given time (c, d and e) or of all the data since 1893 where more than 60 years of recording are available (f) for The Battery, NY (data from PSMSL 2012)

Table 1

Relative sea level trend estimates for all the tide gauges of the United States (data from NOAA, 2012a)

Station name

First year

Year range

To 2006

To 1999

Station name

First year

Year range

To 2006

To 1999

Trend mm/y

Trend mm/y

Trend mm/y

Trend mm/y

Nawiliwili, HI

1955

52

1.53

1.53

Clearwater Beach, FL

1973

34

2.43

2.76

Honolulu, HI

1905

102

1.50

1.50

Cedar Key, FL

1914

93

1.80

1.87

Mokuoloe, HI

1957

50

1.31

1.12

Apalachicola, FL

1967

40

1.38

1.53

Kahului, HI

1947

60

2.32

2.09

Panama City, FL

1973

34

0.75

0.30

Hilo, HI

1927

80

3.27

3.36

Pensacola, FL

1923

84

2.10

2.14

Johnston Atoll

1947

57

0.75

0.68

Dauphin Island, AL

1966

41

2.98

2.93

Midway Atoll

1947

60

0.70

0.09

Grand Isle, LA

1947

60

9.24

9.85

Guam, Marianas Islands

1993

14

8.45

0.10

Eugene Island, LA

1939

36

9.65

9.74

Pago Pago, American Samoa

1948

59

2.07

1.48

Sabine Pass, TX

1958

49

5.66

6.54

Kwajalein, Marshall Islands

1946

61

1.43

1.05

Galveston Pier 21, TX

1908

99

6.39

6.50

Chuuk, Caroline Islands

1947

49

0.60

0.68

Galveston Pleasure Pier, TX

1957

50

6.84

7.39

Wake Island

1950

57

1.91

1.89

Freeport, TX

1954

53

4.35

5.87

Bermuda

1932

75

2.04

1.83

Rockport, TX

1948

59

5.16

4.60

Eastport, ME

1929

78

2.00

2.12

Port Mansfield, TX

1963

44

1.93

2.05

Bar Harbor, ME

1947

60

2.04

2.18

Padre Island, TX

1958

49

3.48

3.44

Portland, ME

1912

95

1.82

1.91

Port Isabel, TX

1944

63

3.64

3.38

Seavey Island, ME

1926

76

1.76

1.75

San Diego, CA

1906

101

2.06

2.15

Boston, MA

1921

86

2.63

2.65

La Jolla, CA

1924

83

2.07

2.22

Woods Hole, MA

1932

75

2.61

2.59

Newport Beach, CA

1955

39

2.22

2.22

Nantucket Island, MA

1965

42

2.95

3.00

Los Angeles, CA

1923

84

0.83

0.84

Newport, RI

1930

77

2.58

2.57

Santa Monica, CA

1933

74

1.46

1.59

Providence, RI

1938

69

1.95

1.88

Rincon Island, CA

1962

29

3.22

3.22

New London, CT

1938

69

2.25

2.13

Santa Barbara, CA

1973

34

1.25

2.77

Bridgeport, CT

1964

43

2.56

2.58

Port San Luis, CA

1945

62

0.79

0.90

Montauk, NY

1947

60

2.78

2.58

Monterey, CA

1973

34

1.34

1.86

Port Jefferson, NY

1957

36

2.44

2.44

San Francisco, CA

1897

110

2.01

2.13

Kings Point, NY

1931

76

2.35

2.41

Redwood City, CA

1974

33

2.06

NA

The Battery, NY

1856

151

2.77

2.77

Alameda, CA

1939

68

0.82

0.89

Sandy Hook, NJ

1932

75

3.90

3.88

Point Reyes, CA

1975

32

2.10

2.51

Atlantic City, NJ

1911

96

3.99

3.98

Port Chicago, CA

1976

31

2.08

NA

Cape May, NJ

1965

42

4.06

3.88

North Spit, CA

1977

30

4.73

NA

Philadelphia, PA

1900

107

2.79

2.75

Crescent City, CA

1933

74

−0.65

−0.48

Reedy Point, DE

1956

51

3.46

NA

Port Orford, OR

1977

30

0.18

NA

Lewes, DE

1919

88

3.20

3.16

Charleston, OR

1970

37

1.29

1.74

Ocean City, MD

1975

32

5.48

NA

South Beach, OR

1967

40

2.72

3.51

Cambridge, MD

1943

64

3.48

3.52

Garibaldi, OR

1970

37

1.98

NA

Chesapeake City, MD

1972

35

3.78

NA

Astoria, OR

1925

82

−0.31

−0.16

Baltimore, MD

1902

105

3.08

3.12

Toke Point, WA

1973

34

1.60

2.82

Annapolis, MD

1928

79

3.44

3.53

Neah Bay, WA

1934

73

−1.63

−1.41

Solomons Island, MD

1937

70

3.41

3.29

Port Angeles, WA

1975

32

0.19

1.49

Washington, DC

1924

83

3.16

3.13

Port Townsend, WA

1972

35

1.98

2.82

Kiptopeke, VA

1951

56

3.48

3.59

Seattle, WA

1898

109

2.06

2.11

Colonial Beach, VA

1972

32

4.78

5.27

Cherry Point, WA

1973

34

0.82

1.39

Lewisetta, VA

1974

33

4.97

4.85

Friday Harbor, WA

1934

73

1.13

1.24

Gloucester Point, VA

1950

54

3.81

3.95

Ketchikan, AK

1919

88

−0.19

−0.11

Sewells Point, VA

1927

80

4.44

4.42

Sitka, AK

1924

83

−2.05

−2.17

Portsmouth, VA

1935

53

3.76

3.76

Juneau, AK

1936

71

−12.92

−12.69

Chesapeake Bay Brdg T, VA

1975

32

6.05

7.01

Skagway, AK

1944

63

−17.12

−16.68

Oregon Inlet Marina, NC

1977

30

2.82

NA

Yakutat, AK

1979

28

−11.54

−5.75

Beaufort, NC

1953

54

2.57

3.71

Cordova, AK

1979

28

2.57

6.97

Wilmington, NC

1935

72

2.07

2.22

Valdez, AK

1979

28

−4.92

−0.34

Southport, NC

1933

74

2.08

NA

Seward, AK

1964

43

−1.74

−1.46

Springmaid Pier, SC

1957

50

4.09

5.17

Seldovia, AK

1964

43

−9.45

−9.93

Charleston, SC

1921

86

3.15

3.28

Nikiski, AK

1973

34

−9.80

−10.71

Fort Pulaski, GA

1935

72

2.98

3.05

Anchorage, AK

1972

35

0.88

2.76

Fernandina Beach, FL

1897

110

2.02

2.04

Kodiak Island, AK

1975

32

−10.42

−12.08

Mayport, FL

1928

79

2.40

2.43

Sand Point, AK

1972

35

0.92

0.07

Daytona Beach Shores, FL

1925

59

2.32

NA

Adak Island, AK

1957

50

−2.75

−2.63

Miami Beach, FL

1931

51

2.39

2.39

Unalaska, AK

1957

50

−5.72

−6.44

Vaca Key, FL

1971

36

2.78

2.58

Guantanamo Bay, Cuba

1937

35

1.64

1.64

Key West, FL

1913

94

2.24

2.27

Lime Tree Bay, Virgin Is

1977

30

1.74

NA

Naples, FL

1965

42

2.02

2.08

Charlotte Amalie, Virgin Is

1975

32

1.20

0.50

Fort Myers, FL

1965

42

2.40

2.29

San Juan, Puerto Rico

1962

45

1.65

1.43

St. Petersburg, FL

1947

60

2.36

2.40

Magueyes Island, Puerto Rico

1955

52

1.35

1.24

A minimum of 60 years of recording are needed to compute a sea level longer-term trend cleared of all the shorter-term oscillations up to the Atlantic multi-decadal oscillation of period 60 years (some other references in the literature to the approximately 60-year cycle are provided by Burton 2012 and a detailed dissection of Sallenger et al. 2012 is provided by Tisdale 2012). The sea level acceleration is then the variation in time of the SLR. Therefore, it is more reasonable to compute the sea level acceleration by fitting the 60-year SLR curve than just using two ad hoc selected values of 30-year SLR, incidentally in a valley and a peak of the typical valley and peak oscillations. This more grounded analysis proves that contrary to the claim of Sallenger et al. (2012), there is no such a thing like a hot spot of positive sea level acceleration along the Atlantic coast of the United States.

Figure 1 presents for The Battery, NY, the measured monthly averages and their deviations versus the linear trend (a, b), the computed SLR obtained by linear fitting of the last 20, 30 and 60 years of data up to any given time (c, d and e) or all the data since 1893 where more than 60 years of recording are available (f). The record spans 1856–2012, but there is a significant gap, 1878–1893. Therefore, only the data from 1893 are used to compute trends. The visual scanning of the monthly departures from a smooth, long-term linear trend in Fig. 1a, b shows no sign of sharp departures. The SLR with the larger 60-year time window oscillates without too much of a sharp positive acceleration in between 2.40 and 3.50 mm/year about the long-term trend of 2.98 mm/year. The amplitude of the oscillations increases reducing the time windows. With the 30 or even worse with the 20-year time window, it is possible to compute unrealistically high- or low-sea level rises absolutely not representative of the long-term trend.

It is clear from this figure that does not make any sense to compute one specific 30-year SLR in December 2009 and compare this 30-year SLR with the December 1979 value. In the specific location of The Battery, NY, the value of the December 1953 30-year SLR is larger than the December 2009 value, but obviously Sallenger et al. (2012) do not use this comparison to prove that the sea levels are decelerating.

The only information of interest in Fig. 1 is eventually provided by the linear fitting of the SLR curve. Whether this curve is moving upwards or downwards is certainly more valuable information that what can be learned from the comparison of two ad hoc selected values. Our conclusion from Fig. 1 is that apart from the noise in the measurements, there is not too much to claim the existence of a positive or a negative acceleration of the SLR in this location.

Table 1 presents the mean sea level (MSL) trend for the United States proposed by the National Oceanic and Atmospheric Administration (NOAA 2012a). This table presents the trends up to 1999 and up to 2006, and eventually, it clearly shows a globally decelerating rather than a positively accelerating trend. The United States sea level trends table on the NOAA website is not an annually created product. The latest United States sea level trends table is derived from two NOAA Technical Reports (NOAA 2001, 2009). Considering the data updated to 1999 for 116 stations, the average SLR is 1.71 mm/year. For the same 116 stations, the data updated to 2006 give an SLR of 1.56 mm/year. For all the 128 United States locations of 2006, the average sea SLR is 1.67 mm/year, but the additional 12 stations do not have a prior counterpart. Therefore, the only consideration that may be globally inferred from that table is eventually that the United States sea levels are globally decelerating. Considering only the 34 stations from Eastport, ME, to Wilmington, NC, with SLR computed up to 1999 and up to 2006 in Table 1, the trend remains of deceleration. Therefore, the hotspot of accelerated sea level rise of Sallenger et al. (2012) is actually a region where the sea levels are possibly decelerating less than the average but still decelerating 1999 to 2006 in the analysis of Table 1. As shown in Fig. 1c, d, also this analysis is not free of criticism, but certainly less questionable than the comparison of two 30-year SLR in a peak and a valley of the 60 years multi-decadal oscillation of Sallenger et al. (2012). More than the Table 1, it is the visual scanning of the monthly departures from a smooth, long-term linear trend for all the 128 stations of the United States (as well as for all the 195 other global locations proposed by the National Oceanic and Atmospheric Administration NOAA, 2012b) that shows no sign of sharp departures and rules out the acceleration claim.

2 Conclusions

Minimum of 60 years of tide gauge recording are needed to compute a long-term SLR cleared of all the shorter-term oscillations in the Atlantic.

The sea level acceleration is eventually the variation in time of the SLR, and not the comparison of two values of SLR selected ad hoc in the SLR curve.

There is no such a thing like a hot spot of positive sea level acceleration along the Atlantic coast of the United States north of Cape Hatteras, where the sea levels only oscillates about the longer-term trend.

Copyright information

© Springer Science+Business Media B.V. 2012