Effects of Sea Level Decadal Variability on Acceleration and Trend Difference*

Transcription

1 Effects of Sea Level Decadal Variability on Acceleration and Trend Difference* James Houston 1 and Robert Dean 2 ¹ Army Engineer Research and Development Center, Corps of Engineers 2 Department of Civil and Coastal Engineering, University of Florida * Based on Houston and Dean, 2012, Journal of Coastal Research (Accepted)

2 Sea Level Definition of Acceleration Car going a steady 120 miles/hr is moving fast, but not accelerating Velocity = Trend = Rate of change of sea level (mm/yr) Acceleration = Rate of change of trend (mm/yr 2 ) Time (Years)

3 Sea Level Rise not Constant in Time - Has Decadal Variability Likely Caused by Weather Variability About 20-yr oscillation 1.7 mm/yr Holgate (2007)

4 Sea Level Rise not Constant in Time - Has Decadal Variability Likely Caused by Weather Variability X 40 years Calculated Acceleration Depends on Record Length X Holgate (2007)

5 Sea Level Rise not Constant in Time - Has Decadal Variability Likely Caused by Weather Variability X X Calculated Acceleration Depends on Record Length 40 years Holgate (2007)

6 Sea Level Rise is Not Spatially Uniform Like a Bathtub Filling with Water

7 Sea Level Change Is Not Spatially Uniform 3-4 times world average Sea level falling Satellite altimeter measurements over 19 + years

8 Sea level rise in 100 yrs if acceleration persists + 5 m Douglas (1992) All tide gauge records in the world with length 10 years + 1 m - 1 m - 5 m

9 Sea level rise in 100 yrs if acceleration persists +10m Houston and Dean (2012) +5m All tide gages in world (1123) with lengths 10 yr 75 yrs - 5m Douglas (1992) used only records 75 years - 10m

10 Violating the Prime Directive PRIME DIRECTIVE - Use record lengths > ~ 75 yrs to determine sea level acceleration and don t trust results where this criterion is violated Sallenger et al (2012) consider yr records, leading to invalid conclusions 900 world media outlets picked up the Sallenger story of a hot spot of sea level rise along the east coast Rahmstorf and Vermeer (2011) use record lengths as short as 30 yrs to erroneously claim their model and projections superior to those of the Intergovernmental Panel on Climate Change

11 Sallenger et al Use Trend Difference = T2-T1 20-Year Record 20-Year Record Trend Difference ~ Acceleration * Record Length

12 Trend Difference Versus Record Length All tide gages in world (1123) with lengths 10 yr Significant scatter even for 100-yr records

13 Sallenger et al (2012) Trend Difference for 40-Year Period Centered in 1990 New York Hotspot Sallenger et al (2012)

14 Sallenger et al (2012) obtained trend difference of 3 mm/yr for 40-yr period centered in 1990 They projected This trend difference to 2100

15 They projected This trend difference to 2100

16 Sallenger et al (2012) Trend Difference for 40-Year Period Centered in 1990 New York Fernandinaa Neutral Sallenger et al (2012)

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18 Galveston Cold Sallenger et al (2012)

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20 San Francisco Cold Sallenger et al (2012)

21 Bromirski et al (2011)

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24 Sallenger et al (2012) Violate prime directive that requires record lengths > ~ 75 yrs to determine the underlying acceleration By taking short records, they just see decadal variations, not underlying trends It is not valid to project trend difference based on one 40-yr period because trend difference varies every year They say, Trend differences for windows longer than 72 yr were not significantly different than zero. OF COURSE! When they analyze records of proper length, the east coast is not even a lukewarm spot of sea level acceleration

25 Rahmstorf and Vermeer (2011) Based on Rahmstorf and Vermeer model Based on Church and White (2006) worldwide data >75 yr record lengths ~ 60 to 30-yr record lengths They calculate acceleration from beginning year to 2001 and plot value at beginning year

26 Synthetic Record Dots are worldwide data of Church and White (2006) Trend 0.8 mm/yr Trend 1.9 mm/yr Trend change ~ Two Linear Trends yr decadal oscillation with 5-mm amplitude yr decadal oscillations with 4-mm amplitude

27 Synthetic Record Versus Data Synthetic Record Trend Change Decadal Variations Data of Church and White

28 Acceleration Due to Trend Change Decadal variations set to zero Dip from ~ due primarily to trend change in 1926 Rahmstorf and Vermeer claim the dip from ~ 1895 to 1930 is due to temperature changing little from 1940 to 1980 Acceleration from matches data Acceleration due to trend change Data of Church and White Zero after ~ 1926

29 Acceleration Due to Decadal Variations Trend change set to zero Acceleration from 1940 due to decadal variations Acceleration from decadal variations Negative contribution Data of Church and White

30 Synthetic Record Versus Data Linear trends and decadal oscillations explain dip from ~ and acceleration after 1940 Decadal oscillations and linear trends Data of Church and White

31 Rahmstorf and Vermeer, 2011 Violate the prime directive by considering records as short as yrs, which are dominated by decadal variations The trend change + decadal oscillations from 1917 to 1933 produce the dip in acceleration from ~ 1895 to 1930 Decadal variations cause the acceleration beginning in ~ 1940 Their model does not include the trend change or decadal variations that determine the curve they claim shows their model to be superior to that of the Intergovernmental Panel on Climate Change

32 Conclusions Tide records > ~ 75 yrs must be used to determine acceleration because decadal variations dominate shorter records and obscure the underlying acceleration It is not valid to project sea level rise based on short records Journal papers are not always correct - Just require 2 of 3 reviewers approval - The Intergovernmental Panel on Climate Change (IPCC) has > 40 eminent authors who agree on sea level projections and several hundred reviewers conduct two detailed reviews - Use sea level projections of IPCC (Sept, 2013)