Sea levels are rising faster than previously estimated, which could significantly impact maritime jurisdictional limits and sovereignty over offshore areas. As sea levels rise, coastal baselines and the limits measured from them will shift inland. This may reduce the size of countries' exclusive economic zones and cause islands to be reclassified, impacting maritime claims. Nations could build defenses to preserve coastlines, fix baselines legally through charts, or fix their maritime limits, but these options all pose challenges for balancing certainty of claims with changing physical coastlines. Significant implications could include loss of jurisdiction over resources, boundary disputes, and conflict.

1. Sea Level Rise and Shifting Maritime
Jurisdictional Limits
Clive Schofield
Australian National Centre for Ocean Resources and Security (ANCORS)

2. Sea Level Rise
• IPCC’s estimated range of sea level rise: 0.38-
0.59m by the end of the century?
• Growing consensus that this estimate is overly
conservative
• Great uncertainty over the critical questions of
how much and how quickly?

3. Maritime Jurisdictions Zones
The
Area
200 M
Sea Level
12 M
Contiguous
zone
Territorial
sea
12 M
Exclusive
Economic Zone (EEZ)
Water Column,
Sea-bed, Subsoil
Rise Deep
Ocean
Internalwaters
TerritorialSeaBaseline
(Extended
Continental Shelf)
Continental Shelf
Sea-bed, Subsoil, Sedentary Species
High Sea
Shelf
Lower
Slopemadeandi@ugm.ac.id © 2008
Upper
Slope Plateu
or
Terrace

4. Migrating Baselines = Shifting Limits
• Maritime jurisdictional limits measured from
baselines:
 Predominantly normal baselines, low-water line baselines
• Traditional interpretation: ambulatory baselines and
consequently shifting limits
 Coastlines dynamic – low water line susceptible to change
 As normal baselines move, the limits drawn from them also
shift
• Not a new phenomenon
• As sea level rises so the low-water line migrates inland
• Dramatic horizontal shifts to normal baselines possible
from slight changes to sea level vertically

5. Impacts on Islands
• Sea level rise/shifting baselines will also impact
on the classification of insular features
• Most common normal baseline used, Lowest
Astronomical Tide (LAT) – a very low low water
line
• Critical basepoints may be unstable or
ephemeral insular features
 Vulnerable to sea level rise leading to downgrading of
islands to mere rocks or low-tide elevations
 Impact on capacity to generate claims to maritime
jurisdiction

6. Implications
• Implications for:
 Extent and limits of maritime claims
 Enforcement issues
 Delimitation of maritime boundaries
• Loss of jurisdiction over vital marine resources
• Jurisdictional uncertainty
• Potential for conflict

7. Potential Responses
• Fix normal baselines physically
 Can key basepoints be preserved through sea
defences, ‘building-up’ and/or reclamation?
 Long tradition and an option for critical basepoints but
unrealistic for long coastlines?
• Fix normal baselines legally
• Fix the limits of maritime zones

8. Okinotorishima: Maritime Claims

9. Okinotorishima

10. Okinotorishima

11. Physical defences
unrealistic for long
coastlines?

12. Fix Normal Baselines Legally
• Choice of chart depicting normal baseline left up to the
coastal State (LOSC, Article 5)
• Chart the legal document
• Can a coastal State therefore choose a chart that is
advantageous to it?
 What if there is a difference between the low water line shown
on the chart and reality?
• The drafters of the Convention did not anticipate sea
level rise
• BUT: Ambulatory baselines may be fixed with straight
baselines on unstable coasts
 Connection to the low water line still required

13. Fixing Limits and Boundaries
• Once agreed maritime boundaries remain fixed
even though the baselines used to construct
them may regress
 What if the territory in question disappears entirely?
• The outer limits of the continental shelf may also
be fixed as “final and binding”
• Fix (declare) maritime limits
 Provides the advantage of certainty and the
preservation of existing maritime claims
 BUT: Increasing tension between fixed limit and
receding or disappearing normal baseline it is
measured from