Note: This is part of a longer article that was submitted as a comment to the US Department of Fish and Game in
response to proposed regulations to restrict access to US west coast beaches to protect the western snowy plover. The
restriction of additional beach area was proposed to compensate for loss of beach due to ‘sea level rise caused by a
warming trend associated with climate change’. The full article can be found at:
(Click on the red .pdf button, lower right to access the full .pdf file)
|SEA LEVEL RISE: NO CAUSE FOR ALARM
Based on the discussion presented in the full comment [Clark, 2011], there is no evidence of carbon
dioxide induced global warming and there should be no expectation of any increase in sea levels
beyond the trends already measured in the tide gauge data. It should also be clear that all of the
alarmist projections of sea level rise in the IPCC ‘scenarios’ are based on invalid modeling assumptions.
None of the climate simulation results derived from the use of radiative forcing should be allowed as
evidence in the analysis of sea level data. This includes data from papers published in such ‘respected’
scientific journals as Nature, Science and PNAS. It is also important to understand that each coastline
segment around an ocean basin can have its own specific trend in sea level change. A one size fits all
global average rise in sea level is not a very useful concept. The starting point for any discussion of
trends in sea level along the western coast of the U. S. is the measured tide gauge data along that
coast. This may be augmented with tide gauge measurements from other regions and satellite altimetry
data, provided that the limits of their local applicability are clearly understood.
Tide Gauge Data
The determination of changes in sea level requires a careful analysis of the many factors that influence
the measurements. Tide gauges simply record the local sea level measured relative to the gauge.
Assuming that the foundations of the gauge structure are stable, the land on which the gauge is situated
may be moving because of the influence of factors such as plate tectonics, changes in ice thickness and
local water table level fluctuations. Tide levels are influenced by the lunar/solar gravitational cycle,
weather patterns and longer term climate trends such as ice melting or formation. In addition, the
volumes of ocean basins may vary with time because of sea floor spreading. Since the last glacial
maximum, 20,000 years BP (before present), mean sea level has risen approximately 120 m. This rise
was produced by the melting of ice sheets at mid to high latitudes that were over 1 km thick. For
example, the Laurentide Ice Sheet covered most of Canada and the northern part of the U. S. However,
as the weight of the ice was removed, this produced a significant uplifting of the land that was under the
ice. Figure 2-3, in the full comment [Clark, 2011] shows the measured changes in sea level at various
sites around the world [Lambeck, 2004]. Hudson Bay has risen over 250 m since the last ice age. This
illustrates some of the effects that need to be addressed in the determination of sea level changes. In
the State of California, the coastal regions south of San Francisco are located on the Pacific Plate. The
boundary of this tectonic plate is the San Andreas Fault. This is a slip fault with the North American
Plate. The fault line runs close to the coast north of San Francisco and moves offshore just south of
Eureka. To the north, the coast is located on the North American Plate [USGS, 2011]. Here there are
active volcanic regions, notably adjacent to Mount St. Helens where volcanic activity may contribute to
changes in sea level.
The two longest west coast tide gauge records are from San Francisco, starting in 1855 and Seattle,
starting in 1900. The monthly mean sea level from these two gauges is shown in Figure 5-1. All of the
tide gauge data used here is taken from the NOAA website and used ‘as received’ [NOAA, Tides and
Currents, 2011]. A simple linear fit to the date sets using the Excel ‘trendline’ routine gives sea level
rises of 1.4 mm per year for San Francisco and 2 mm per year for Seattle. The total sea level rise for
San Francisco over 155 years was 217 mm or 8.5 inches. For Seattle the corresponding rise was 220
mm or 8.7 inches over 110 years. This is hardly any cause for alarm. As shown in Figure 4-8in the full
comment [Clark, 2011], the air temperature of the lower troposphere has not increased since 1998.
Similarly, the current period of high sunspot activity appears to have ended. The current sunspot cycle,
number 24 is estimated to peak at about half of the number of sunspots of cycle 23. This is analogous
to the start of the Dalton Minimum at the beginning of the nineteenth century. Simple inspection of the
tide level trends in Figure 5-1 shows a recent downward trend. To match IPCC predictions, the tide level
slopes would have to more than double to over 5 mm per year for a 500 mm rise by 2100. This should
already be happening based on rising atmospheric CO2 levels. Such alarmist projections are clearly
|Figure 5-1: Tide gauge records of monthly mean sea level for San Francisco from
1855 (lower trace) and for Seattle from 1900 (upper trace).
Figure 5-2 shows the monthly mean sea level data from Figure 5-1 and 12 other tide gauges along
linear fits to the data in Figure 5-2. Table 5-1 presents the summary data including the period of
record. Figure 5-2 shows the monthly mean sea level data from Figure 5-1 and 12 other tide gauges
along the linear fit parameters (ft), the maximum and minimum recorded MSL values and the difference
the western U. S. coast. Figure 5-3 shows the rate of increase in mean sea level (mm/yr) derived from
the western U. S. coast. Figure 5-3 shows the rate of increase in mean sea level (mm/yr) derived from
linear fits to the data in Figure 5-2. Table 5-1 presents the summary data including the period of record,
the linear fit parameters (ft), the maximum and minimum recorded MSL values and the difference
between them and the linear slope increase in mm per year. The last column is the data plotted in
Figure 5-3. The mean sea level anomaly differences were calculated by subtracting the mean from
each data set. Although it is difficult to see in Figure 5-1 and 5-2, many of the features in the tide data
are not random noise but fluctuations caused by phenomena such as the ENSO oscillation. This is
illustrated in Figure 5.4 which shows the tide gauge anomaly data and their average for the decade from
1990 to 2000. The ENSO peak for 1997-1998 can clearly be seen in the data. In order to investigate
the relationship between the tide gauge data and the ENSO index, the tide anomaly data was smoothed
using a 1 year rolling average and compared to the monthly ENSO index smoothed with the same 1 year
rolling average. A least squares minimization technique was used to scale the ENSO index to match the
tide gauge average. The best fit was found with a 0.13 scaling factor. This is shown in Figure 5-5. The
effect of the ENSO oscillation in the tide gauge data is very apparent. From Figure 5-4 it can be seen
that the 1997-8 ENSO event produced an increase in mean sea level of approximately 10 inches (250
mm). This is larger that the increase in mean sea level measured from the linear slope of the tide gauge
record for the past 150 years.
|Figure 5-2: Monthly mean sea level data from 14 west coast U. S. tide gauges
|Figure 5-3: Mean sea level increases (mm/year) derived from linear fits to the
data in Figure 5-2.
|Table 5-1: Tide gauge mean sea level data summary: period of record, linear fit (ft), minimum and
maximum msl values recorded and linear slope in mm. This last column is plotted in Figure 5-3.
|Figure 5-4: Monthly tide gauge anomaly data from 1990 to 2000. The effect of the 1997-8
ENSO event can clearly be seen in the data.
|(0.13 scale factor). The effect of the ENSO oscillation in the tide gauge data is
In order to investigate the recent decrease in the slope of the tide gauge data, the average anomaly
data from 1930 to 2010 was divided into four 20 year periods and a linear fit to each data subset was
made. The annual increases for the four periods were 1.6, 1.9, 1.4 and -0.1 mm per year. This clearly
shows that the rate of increase in mean sea level is slowing down along the western coast of the U. S.
When different time periods and reference averaging periods are selected, the slope of the tide data will
change. However, the general downward trend is quite clear in the data since 1990.
|Figure 5 6: Linear fit to the average tide gauge anomaly data using 20 year
interval subsets. The recent downward trend can clearly be seen in the 1990 to
2010 data subset.
Comparison with Other Tide Gauge and Satellite Altimetry Measurements.
Annual mean sea level data from 1870 was recently published by Houston and Dean . Their data,
from various sources is shown in Figure 5-7. The data shows that the annual increase in sea level was
approximately 1 mm per year from 1870 to 1920 and increased to approximately 2 mm per year from 1920 to
2000. Figure 5-8 shows the sea level data for San Francisco smoothed with a 1 year rolling average and
offset by -50 mm superimposed on Figure 5-7. The two curves overlap quite well and the effect of ocean
oscillations such as ENSO can clearly be seen in the data. The recent decrease in slope can also be seen in
the San Francisco data.
Figure 5-9 shows the trends in regional mean sea level from satellite radar altimetry measurements over
the available satellite observation period from 1993 to 2010 [AVISO, 2011]. The main region of increasing
sea level is the Pacific warm pool. The dark red region just left of center in the map, above Australia has a
sea level increase of at least 10 mm/yr, or 180 mm (7 inches) over 18 years. The region along the west coat
of the U. S. shows a slight decreasing trend in sea level. It is important to note that sea level and ocean
temperature profiles are related. The rise in sea level in the Pacific warm pool region is caused by increases
subsurface temperatures down to depths of approximately 250 m. These rises in sea level are highly unlikely
to propagate to the west coast of the U. S. because of the cooling that occurs once the warm water is
transported away from the Western Pacific. The water is circulated around the N. Pacific gyre, as shown in
Figure 3-16 in the full comment [Clark, 2011]. Cooling occurs at higher latitudes as the gyre transports the
water across the central N. Pacific Ocean.
|Figure 5-7: Mean sea level data from Houston and Dean .
|Figure 5-8: San Francisco tide gauge data superimposed on the averages from
Houston and Dean . The SF data were smoothed using a 1 year rolling average
and offset by -50 mm to match Figure 5-7.
|Figure 5-9: Satellite altimetry trends over the satellite observation period. Note the increase in sea
level within the Pacific warm pool [AVISO, 2011]
The practice of presenting global or ocean basin averages of sea level trends is, to say the least,
misleading. It is incorrect to assume that all of the Pacific Ocean tide gauges will show the same trend.
sea level over the 1992 to 2010 period whereas those in the S. W. Pacific region should show a larger
increase. Figure 5-10 shows the satellite altimetry data for the Pacific basin mean sea level from 1993
to 2010 compared to the average of 14 western U. S. tide gauges from Figure 5 6 over the same time
period. The altimetry average gives an increase of 2.6 mm per year. The tide gauge average gives a
decrease of -5 mm per year. Figure 5-11 shows tide gauge data from four gauges located in the S. W
Pacific region [U. Hawaii Sea Level Center, 2011]. All four show increases in mean sea level of
approximately 20 cm (8 inches) over the 1993 to 2010 period. This is consistent with Figure 5-9. The
SEAFRAME study of sea levels on 12 Pacific Islands also indicates that there no cause for alarm in sea
level rise once the data is corrected for the effects of cyclones and other factors that are not part of the
overall sea level trends [Gray, 2010].
|Figure 5-10: Pacific basin average sea level from Satellite altimetry 1993 to 2010
compared to the U. S. west coast tide gauge average over the same period. The tide
gauges show a decrease of -0.5 mm per year. The basin altimetry data shows an
increase of 2.6 mm per year. This is dominated by the Pacific warm pool rise.
|Figure 5-11: Tide gauge data from the S. W. Pacific region showing 20 cm rises in mean sea level from
1993 to 2010 (U. Hawaii Sea Level Center).
The results from this analysis of western U. S. tide gauge data and comparison to other tide gauge
and satellite altimetry data make it clear that there will be no alarming rise in sea level over the next
century. Such predictions, as given by the IPCC are based on invalid modeling assumptions and should
not be included in any discussion of mean sea level trends. Based on current trends in the sunspot
index and the PDO/ENSO oscillations, the increase in sea level in the 21 st century should not be more
than that in the previous century and may be less.
Figure A-1 shows plots of the individual tide station records used in the analysis in Section 5.1. The
station record data, including the straight line fits are given above in Table 5-1.
|APPENDIX : WESTERN U. S. TIDE GAUGE DATA
|Figure A-1: Plots of the tide gauge data used in the analysis in Section 5.1.
|Akasofu, S-I , Natural Science 2(11) 1211-1224 (2010), ‘On the recovery from the Little Ice Age’
AVISO, Mean Sea level products and images, [Accessed 5/14/2011] http://www.aviso.oceanobs.
Clark, R. 2011 ‘There is no carbon dioxide induced global warming and there can be no increase in sea
level above the present long term trend’
(click on th .pdf button, lower right to access this file, it is ~ 100 pages long)
Gray, V. R., South Pacific sea level: a reassessment, SSPI, Aug 16, 2010 [Accessed 5/18/2011]
JISAO, PDO Data, http://jisao.washington.edu/pdo/PDO.latest [Accessed 5/11/2011]
JMA, ENSO Data, ftp://www.coaps.fsu.edu/pub/JMA_SST_Index/jmasst1868-today.filter-5 [Accessed
Lambeck, K., Comptes Rendus Geoscience 336 667-689 (2004), ‘Sea level change through the last
glacial cycle: geophysical, glaciological and paleogeographic consequences’
Morner, N-A., 21st Century Science and Technology, pp.7-17 (Fall 2010), ‘There is no alarming sea
NOAA, ENSO http://www.ncdc.noaa.gov/teleconnections/enso/ [Accessed 5/10/2011]
NOAA, Tides and Currents, Monthly tide data, [Accessed 5/14/2011]
U. Hawaii, Sea level Center, http://uhslc.soest.hawaii.edu/ [Accessed 5/12/2011]
USGS, The San Andreas Fault, http://pubs.usgs.gov/gip/earthq3/contents.html, [Accessed 5/14/2011]
|Dr. Roy Clark
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