Technical Notes

Acronyms

PSMSL

Permanent Service for Mean Sea Level

SLR

Sea level rise

VLM

Vertical land movement

SONEL

Système d'Observation du Niveau des Eaux Littorales

CMIP5

Couples Model Intercomparison Project Phase 5

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Glossary

Normalized value

Adjusting values measured on different scales to a notionally common scale.

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Overview

Globally important cultural and economic features are situated in the coastal and near coastal regions of the world. Assets, such as cities and their related infrastructure, ports, transport and energy corridors, mass and boutique tour¬ism sites and cultural heritage sites are already know to be situated in vulnerable coastal locations. All these and more types of sites will become increasingly vulnerable as sea levels rise. Global circulation models of sea level rise combined with data on vertical land movement offer opportunities for data presentation previously unavailable to such a wide audience. The application of Esri tools and know-how and other third party software has made this possible in this app.

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Data and Methods

The GCM data used in this App is from CMIP5. For more information on CMIP5 please visit: http://cmip-pcmdi.llnl.gov/cmip5/guide_to_cmip5.html. It is important to note that not all models available in the CMIP5 database contain data on all climate variables.

The monthly changes in SLR of 28 GCMs between 1986-2005 and 2081-2100 under the RCP4.5 scenario were calculated using a pattern scaling method.

GCM data were retrieved from the Earth System Grid (ESG) data portal for CMIP5, including: the sea surface height (‘zos’), the global average thermosteric sea level change (‘zostoga’) and the global average sea level change (’zosga’) under the RCP4.5 scenario. For some GCMs, only ‘zosga’ was available and was therefore used instead of zostoga. The data availability is shown in Table 1. Please find details on GCMs and RCP scenarios below in our 2013 Data Manual, and more information on the variables applied can be found at http://www.climatechange2013.org/images/report/WG1AR5_Ch13SM_FINAL.pdf and http://www-pcmdi.llnl.gov/ipcc/standard_output.pdf.

The change in sea surface height was scaled by the change in global average thermal expansion by month following the pattern scaling theory (please see details in our 2013 Data Manual). The sea surface height from GCMs includes the regional variability of dynamic topography changes due to water mass advection, thermohaline circulation and to the wind-driven circulation, but did not include the tidal effects. The changes in global average thermal expansion were calculated by the changes in zostoga if available, or by the changes in zosga.

The value X (m/m) in the patterns is interpreted as “regional sea level may rise X m when the global average sea level rises 1 m”.

No.	GCM	zos	zostoga	zosga
1	ACCESS1-0	True	False	True
2	ACCESS1-3	True	False	True
3	bcc-csm1-1	True	False	True
4	bcc-csm1-1-m	True	False	True
5	CanESM2	True	False	True
6	CCSM4	True	True	True
7	CMCC-CM	True	False	True
8	CMCC-CMS	True	False	True
9	CNRM-CM5	True	True	True
10	CSIRO-Mk3-6-0	True	True	False
11	GFDL-CM3	True	True	True
12	GFDL-ESM2G	True	True	True
13	GFDL-ESM2M	True	True	True
14	GISS-E2-R	True	True	True
15	GISS-E2-R-CC	True	False	True
16	HadGEM2-CC	True	True	False
17	HadGEM2-ES	True	True	False
18	inmcm4	True	True	False
19	IPSL-CM5A-LR	True	True	True
20	IPSL-CM5A-MR	True	False	True
21	MIROC5	True	False	True
22	MIROC-ESM	True	False	True
23	MIROC-ESM-CHEM	True	True	True
24	MPI-ESM-LR	True	True	True
25	MPI-ESM-MR	True	True	True
26	MRI-CGCM3	True	True	True
27	NorESM1-M	True	True	True
28	NorESM1-ME	True	False	True

Table 1: Available GCMs with sea level rise variables in CMIP5 global data

The Representative Concentration Pathways (RCPs) are four greenhouse gas concentration (not emissions) trajectories adopted by the IPCC for its Fifth Assessment Report (AR5). The four RCPs, RCP2.6, RCP4.5, RCP6.0, and RCP8.5, are named after a possible range of radiative forcing values in the year 2100 (of 2.6, 4.5, 6.0, and 8.5 W/m2, respectively) (Table 1).

Table 1. Overview of representative concentration pathways (RCPs) (van Vuuren et al. 2011; Moss et al. 2010; Rojeli et al. 2012)

Description *		CO2 Equivalent	SRES Equivalent	Publication – IA Model
RCP8.5	Rising radiative forcing pathway leading to 8.5 W/m2 in 2100.	1370	A1FI	Raiahi et al. 2007 – MESSAGE
RCP6.0	Stabilization without overshoot pathway to 6 W/m2 at 2100	850	B2	Fujino et al.; Hijioka et al. 2008 – AIM
RCP4.5	Stabilization without overshoot pathway to 4.5 W/m2 2100	650	B1	Clark et al. 2006; Smith and Wigley 2006; Wise et al. 2009 – GCAM
RCP2.6	Peak in radiative forcing at ~ 3 W/m2 before 2100 and decline	490	None	van Vuuren et al., 2007; van Vuuren et al. 2006 - IMAGE

* Approximate radiative forcing levels were defined as ±5% of the stated level in W/m2 relative to pre-industrial levels. Radiative forcing values include the net effect of all anthropogenic GHGs and other forcing agents.

An important element in the process is accounting for variations over a year which can cause higher than average sea levels in some months for certain locations. This seasonal aspect has been taken into account by focusing on the month with the highest current level and comparing this with the month with the highest level in the future. The actual month will be different in different locations.

The App shows a global map of the combined processes of local (absolute) sea level rise and local vertical land movement. The sea level rise values are taken as the median value of an ensemble of 28 GCM’s, under the assumption of the largest greenhouse gas emissions as described by the RCP8.5 scenario in AR5. It also assumes a high climate sensitivity.

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Processing of Vertical Land Movement Data

Vertical land movement (VLM) is a generic term for all processes that impact the elevation at a given locations (tectonic movements, subsidence, ground water extraction), causing land to move up or down. This is typically a slow process with magnitudes commonly between -10 (sinking) and +10 (rising) mm/year.

Local vertical land movement becomes relevant when looking at the local effects of sea level rise. The orders of magnitude are comparable, and VLM can thus either exacerbate or dampen the sea level rise experienced at a coastal location. In a place where VLM is upward (rising, like Norway), the local experienced SLR is smaller (local SLR can even be negative: sea level going down). When VLM is downward (sinking, like Manila), local experienced SLR is stronger.

Because of its (potential) magnitude local VLM must be considered when sea level rise effects are determined on a local scale.

Note that local sea level rise is usually different from the global mean (regardless of VLM), because of variations in currents, the amount of heating of the sea water (responsible for the thermal expansion), as well as the volume (depth) of the sea water affected. This is expressed in the normalized change patterns extracted from GCM-results.

Vertical land movement can be observed directly, or inferred from related measurements.

Direct observations (SONEL)

Direct observations are available through the SONEL initiative (http://www.sonel.org/) whereby VLM is estimated from continuous GPS measurements at fixed locations, often coinciding with tidal observation stations. The latest set of “solutions” (http://www.sonel.org/-GPS-Solutions-.html?lang=en) contains location (lat/lon) and estimates of VLM (mm/year). As there are requirements for determining the trend (length of the period, completeness, quality, stability of the solution), not all stations have an associated value. With time more and more solutions will become available.

Indirect observations (PSMSL)

The Permanent Service for Mean Sea Level (http://www.psmsl.org/) maintains an archive of observed tides. An analysis of the data for these stations to estimate their trends (which are reflecting the rise in sea level), is also available (http://www.psmsl.org/products/trends/trends.txt). Note that not all stations meet the requirements of completeness, total number of observations and quality of measurements.

The local observed sea level rise and local vertical land movement have the following relation:
local observed SLR = local absolute SLR – local VLM
(with VLM>0 means that land is rising, VLM<0 land is sinking)
local absolute SLR = global SLR (over the observation period) * local normalized value (from an ensemble of GCMs)

To determine the global SLR over the period that the tidal observations were made, the following curve is used.

Church and White (2011) data can be downloaded from http://www.psmsl.org/products/ reconstructions/ and http://www.cmar.csiro.au/sealevel/sl_data_cmar.html.

Note: The longest part of the global curve is based on tidal observations (up to 1992, after 1992 satellite observations are used). In order to do that, assumptions needed to be made about the local VLM at each tidal station. A global model (mostly for tectonic movements) was used to do this. This creates a “thinking loop” as we are trying to estimate local VLM from data that has been corrected with a modelled VLM. The assumption is that the averaging of the data around the globe minimizes this bias.

From points to raster (IDW, parameters)

To be able to use VLM in places where it has not been observed, the VLM values in the (SONEL or PSMSL) point locations needed to be interpolated spatially over a grid. ArcGIS has multiple models for spatial interpolation of point values which were tested on their performance noting:

• Ease of use (parameters and inputs needed)
• Ability to reproduce known values at point locations
• Overall “look-and-feel” of the output (homogeneity, reproduction of expected behaviour [like land rising close to the Arctic region, due to rebound from retracting land-ice]))

The conclusion is that the IDW (Inverse Distance Weighted) model is the most useable. The following parameter choices were made:

Parameter setting	Motivation
output cell size = 0.25°x0.25°	to confirm with resolution of SLR-patterns
power = 2.5	dampens the spatial extend of outliers
number of points = 12	creates acceptable spatial coherency
extend = -180,180,-90,90	global coverage

Note: The description of the IDW tool is unclear on how it deals with coordinate system issues. As the station locations are in LAT/LON, the distances between the stations are not simple equations. It is assumed ArcGIS deals with this issue. If this is not the case, there is a bias in the inverse distance weighing. As most stations are relatively close to each other, this will only result in a small error.

The IDW tool does not wrap around the globe (crossing the 360° to 0° meridian). This was managed by executing the IDW tool twice (only for the combined result, see below): once with the 180° meridian centered and once with the 0° meridian centered (the longitudes of the observation stations were either mapped on 0° to 360°, or on -180° to 180°). The resulting images were joined using the following scheme:

The 0° to 360° image was reassembled as: B3+A2+A3+B2, while the -180° to 180°image resulted from A3+B2+B3+A2.

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Results

Discussion

The methodology described combines multiple techniques and datasets to get a best estimate of local vertical land movement around the globe. Its practical usage is limited to the coastlines, where most data is collected, making use in those regions more reliable. The methodology can be reapplied to update the resulting VLM-image when new information from SONEL and/or PSMSL becomes available.

Interpretation

Sea level rise is a very local affair. Multiple variables interact resulting in considerable variation around the world’s coastlines in how sea level rise is expressed locally. The Marine toolbar represents values realized through the application of an ensemble of all the CMIP5 general circulation models that have sea level rise patterns. Across the 28 models there are some where the modelled sea level rise for a location will exceed the ensemble mean while others will be less. People who will use this type of sea level rise data need to be aware of this variability in model outcomes. Moreover, the models are only used to express potential change in sea level rise out to the year 2100 while sea level rise will continue for centuries given the lag in the global climate system set in train by current greenhouse gas concentrations.

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References/Web Links

Church, J. A., & White, N. J., 2011. Sea-level rise from the late 19th to the early 21st century Surveys in Geophysics, 32(4-5), 585–602. doi:10.1007/s10712-011-9119-1.

Douglas, B. C. (1991) Global sea-level rise. Journal of Geophysical Research-Oceans, 96, 6981-6992.

Douglas, B. C. (1997) Global sea rise: A redetermination. Surveys in Geophysics, 18, 279-292.

Fujino, J., R. Nair, M. Kainuma, T. Masui, Y. Matsuoka, 2006. Multi-gas mitigation analysis on stabilization scenarios using AIM global model. Multigas Mitigation and Climate Policy. The Energy Journal Special Issue.

Moss, M., et al. (2010) The next generation of scenarios for climate change research and assessment, Nature, doi:10.1038/nature08823.

Permanent Service for Mean Sea Level (PSMSL), 2014, "Tide Gauge Data", Retrieved 17 Mar 2014 from http://www.psmsl.org/data/obtaining/.

Raiahi K, Gruebler A, Nakicenovic N (2007) Scenarios of long-term socio-economic and environmental development under climate stabilization. Technol Forecast Soc Chang 74(7):887–935.

Rogelj, J., Meinshausen, M., and Knutti, R. (2012). Global warming under old and new scenarios using IPCC climate sensitivity range estimates, 2012, Nature Climate Change, DOI: 10.1038/NCLIMATE1385.

Simon J. Holgate, Andrew Matthews, Philip L. Woodworth, Lesley J. Rickards, Mark E. Tamisiea, Elizabeth Bradshaw, Peter R. Foden, Kathleen M. Gordon, Svetlana Jevrejeva, and Jeff Pugh (2013) New Data Systems and Products at the Permanent Service for Mean Sea Level. Journal of Coastal Research: Volume 29, Issue 3: pp. 493 – 504. doi:10.2112/JCOASTRES-D-12-00175.1.

Smith, S.J. and T.M.L. Wigley, 2006. Multi-Gas Forcing Stabilization with the MiniCAM. Energy Journal (Special Issue #3) pp 373-391.

Solomon, S. 2007. Climate change 2007 : the physical science basis : contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge ; New York: Cambridge University Press.

van Vuuren, D., M. den Elzen, P. Lucas, B. Eickhout, B. Strengers, B. van Ruijven, S. Wonink, R. van Houdt, 2007. Stabilizing greenhouse gas concentrations at low levels: an assessment of reduction strategies and costs. Climatic Change, doi:10.1007/s/10584-006-9172-9.

van Vuuren, D.P., et al. (2011) The representative concentration pathways: an overview. Climatic Change. 109:5-31.

Zervas, C. E. 2001. Sea level variations of the United States, 1854-1999. Silver Spring, Md.: U.S. Dept. of Commerce, National Oceanic and Atmospheric Administration, National Ocean Service.

SONEL: http://www.sonel.org/

PMSML: http://www.psmsl.org/

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