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Prepared by: USINDOPACOM J06 (INDOPACOM.J06.OPLAW@pacom.mil), U.S. Pacific Fleet (N01J), and U.S. Navy Region Legal Service Office Southwest

Last Updated: February 5, 2024 (all prior versions obsolete)

**This TACAID includes legal opinion and analysis that does not necessarily reflect official U.S. government positions

USINDOPACOM J06/SJA TACAID SERIES

TOPIC: IMPACT OF SEA-LEVEL RISE ON MARITIME ZONES

 BOTTOM LINE

● Sea-level rise threatens coastal States worldwide and poses an existential threat to Pacific Island States. 

● USINDOPACOM recognizes the severity of this threat and is committed to working with allies and partners to 

promote stability, security, certainty, and predictability of maritime entitlementsthat are vulnerable to sea-level rise. 

● The United Nations Convention on the Law of the Sea (UNCLOS) does not address the effect of sea-level rise on 

long-established baselines and corresponding maritime zones. 

● As international law in this area develops, many countries see a need to preserve baselines and outer limits of 

maritime zones, and to prevent foreign actors from exploiting uncertainty to the detriment of coastal States.i

● The U.S. position is that sea-level rise caused by climate change should not diminish the maritime zones on which 

island States and other coastal States rely, including for food, livelihoods, and security.ii

● The United States is committed to preserving the legitimacy of maritime zones, and associated rights and 

entitlements, that have been established consistent with international law reflected in UNCLOS and that are not 

subsequently updated despite sea-level rise caused by climate change.iii

● The United States will work with Pacific Island States and other countries toward lawfully establishing and 

maintaining baselines and maritime zone limits and has urged other countries to adopt similar approaches.

iv

WHY THIS MATTERS 

● If maritime zone limits recede landward with contracting baselines, the legal status of affected waters would 

change – e.g., internal waters could become territorial sea (TTS); TTS could become contiguous zone (CZ) and 

exclusive economic zone (EEZ); EEZ could become high seas; and archipelagic baselines could face dissolution as 

the distance between land features increases. 

● These changes would significantly affect the rights of 

coastal States (sovereignty in TTS, resource rights in 

the EEZ, etc.) and foreign States (innocent passage in 

TTS, high-seas freedoms in EEZ, etc.). 

● Without action to ensure stability, security, certainty,

and predictability, the sovereign rights and interests of 

coastal States will remain under threat and foreign

actors could exploit ambiguity in maritime entitlements 

to their benefit and the detriment of coastal States. 

● Pacific Island States are especially vulnerable to sealevel rise and need support from the international 

community to ensure their maritime zones are 

preserved in accordance with international law.v

● The United States steadfastly supports Pacific Island States, to include the Freely Associated States (Republic of 

the Marshall Islands, the Federated States of Micronesia, and the Republic of Palau) with whom the United States 

maintains a unique relationship and obligations under the Compacts of Free Association.vi 

● Raising awareness of the threat posed by sea-level rise to Pacific Island States and other countries may create

opportunities for cooperation to preserve the rights of allies and partners across the Indo-Pacific region.

Image Source: Pacific Islands Forum 
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DETAILED DISCUSSION

Climate Change and Sea Level Rise

● Melting glaciers and ice sheets are adding water to the ocean, and the volume of the ocean is expanding as the 

water warms. Between 1993 and 2021, mean sea levels rose as much as six to eight inches in ocean basins.vii

● As global temperatures continue to rise, so will mean 

sea levels. Models estimate that sea levels could rise

by two to six feet higher than 2000 levels by 2100.viii

● Highlighting one at-risk Pacific Island State, in August 

2023 the Sea Level Change Team at the National 

Aeronautics and Space Administration (NASA) 

released a technical assessment detailing Tuvalu’s 

struggle with rising seas, and concluded based on 

projections that much of Tuvalu’s land area will be 

below the average high tide by 2050.

ix

 

Maritime Boundaries: The Basics

● Under international law reflected in UNCLOS, maritime zones are measured from lawfully drawn baselines.

x

● Unless other special rules apply,xi the normal baseline from which maritime claims of a State are measured is the 

low-water line along the coast as marked on the State’s official charts.xii

● The world’s oceans are divided into two parts: (1) waters that are subject to sovereignty of coastal States 

(internal waters, TTS, and archipelagic waters); and (2) waters beyond the TTS (consisting of the CZ, EEZ, high 

seas) in which all States enjoy high seas freedoms of navigation and overflight and other lawful uses related to 

these freedoms.

xiii

o Internal waters are landward of the baseline. 

Examples include lakes, rivers, and some bays.xiv

o The TTS is a belt of ocean measured seaward 

from the baseline up to 12 nautical miles

(nm).

xv

o Archipelagic waters fall within archipelagic 

baselines.

xvi In archipelagic waters, all States

have the right of archipelagic sea-lanes passage 

through designated sea-lanes and routes 

normally used for international navigation and 

overflight.xvii

o The CZ is an area extending seaward from the 

TTS up to 24 nm from the baseline in which the 

coastal State may enforce its customs, fiscal, 

immigration, and sanitary laws.xviii

o The EEZ is a resource-related zone extending up to 200 nm from the baseline where the coastal State has 

sovereign rights to explore, exploit, conserve, and manage natural resources.

xix

o The high seas include all parts of the ocean seaward of the EEZ. On the high seas, all States enjoy 

freedoms of navigation and overflight and other lawful uses of the seas related to those freedoms.xx

● An island is (1) a naturally formed area of land, surrounded by water, (2) which is capable of sustaining human 

habitation or economic activity of its own and (3) is above water at high tide.xxi A State may claim maritime zones 

including a 12 nm TTS and 200 nm EEZ around an island.xxii

● Rocks, defined as being above water at high tide but unable to sustain human habitation or economic activity, can 

only generate a 12 nm TTS, but not an EEZ.

xxiii

● A low-tide elevation is a naturally formed area of land, surrounded by and above water at low tide, but 

submerged at high tide. A low-tide elevation has no TTS of its own, but may be used as a baseline when it is 

within the TTS of a State.xxiv

To underscore the effect of sea-level rise, Tuvalu’s Foreign 

Minister addressed the 2021 UN Climate Change 

Conference while standing in the ocean. Image source. 
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The Potential Effects of Sea-Level Rise on Coastal State Rights 

● Rising seas mean that coastal areas may soon be underwater; islands may become uninhabitable; rocks may 

become low-tide elevations that are underwater at high tide; and low tide elevations may disappear. 

● The land territory of low-lying Pacific Island States could vanish entirely.xxv

● Receding low-water marks caused by rising seas raise questions about the legal status of affected waters and the 

associated rights of coastal States and foreign States. 

● Absent stability, security, certainty, and predictability of baselines and outer limits of maritime zones, coastal States 

risk losing sovereignty in waters that transition from TTS to waters beyond the TTS and forfeiting resource rights

(fishing, oil, minerals, etc.) in areas of the EEZ that become high seas. 

● States could also be compelled to renegotiate maritime boundary delimitation agreements, which may take 

years and lead to uncertainty and potential clashes between States with overlapping maritime zones.xxvi

● Moreover, foreign actors could exploit ambiguous maritime boundariesto the detriment of coastal States. 

● Many States and their citizens rely on maritime entitlements for food, livelihoods, and security. Diminution of an 

EEZ could devastate a coastal State’s economy by reducing that State’s ability to exclusively extract (or receive 

royalties for the extraction) oil, natural gas, fish, and other resources. 

International Law & State Practice

● UNCLOS does not address the effect of sea-level rise on baselines and corresponding maritime zones.xxvii

● In 2014, the Permanent Court of Arbitration, a non-UN intergovernmental organization that arbitrates disputes of 

international agreements between member states, held

that maritime baselines “must be stable and definitive 

to ensure a peaceful relationship between the States”

and that climate change cannot “jeopardize the large 

number of settled maritime boundaries throughout the 

world.”xxviii

● Furthering this trend, the International Legal Association 

passed a resolution in 2018 that “...baselines and limits 

should not be required to be recalculated should sea 

level change affect the geographical reality of the 

coastline,” affirming a fixed boundaries approach from 

the international legal community.

xxix

● The Pacific Islands Forum issued a landmark 2021 Declaration on Preserving Maritime Zones in the Face of

Climate Change-related Sea-Level Rise, which noted that UNCLOS imposes “no affirmative obligation to keep 

baselines and outer limits of maritime zones under review nor to update charts or lists of geographical 

coordinates once deposited with the Secretary-General of the United Nations.”xxx

● The declaration stated that once maritime zones are lawfully established, “[Pacific Island States] intend to 

maintain these zones without reduction, notwithstanding climate change-related sea-level rise.”xxxi

● A 2023 report by the UN International Law Commission (ILC) found widespread international support for the 

stability of established maritime baselines notwithstanding sea-level rise.

xxxii

● Australia and many Pacific Island States have enacted domestic legislation to affix maritime boundary points.

● Pacific Island States have submitted fixed boundaries to the UN in accordance with UNCLOS. Some States, such as 

New Zealand, included annotations in their submissions stating that there is no obligation to submit additional 

coordinates for changes that occur due to due to sea level rise.xxxiii

● A growing number of developed nations with alliances, partnerships, and territorial interests in the Pacific support 

preserving existing maritime zones, to include the United States, the United Kingdom, Germany, and France.

xxxiv

● Some nations, including the PRC and Russia, have expressed caution regarding the preservation of maritime 

zones.

xxxv In a 2021 statement to the U.N. ILC, the PRC posited that State practice on sea-level rise was not

“established” and “overemphasizing regional practice may exacerbate the fragmentation of legal rules.”

● The PRC’s statement seemingly reflects a double-standard given the PRC’s claims to “historic rights” in the South 

China Sea, which exemplify a PRC-centric historical narrative and the fragmentation of legal rules due to a highly 

regionalized interpretation of both history and law.

xxxvi

Leaders gather at the White House for the second U.S.-Pacific 

Islands Forum Summit in September 2023. From Reuters.
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U.S. Policy

● The United States supports the Pacific Islands Forum’s declaration; recognizes the need for stable maritime 

zones in the face of sea-level rise caused by climate change; and is committed to preserving the legitimacy of 

existing maritime zones and their associated rights 

and entitlements.xxxvii

● At the U.S.-Pacific Islands Forum Summit in 

September 2023, President Biden announced that 

sea-level rise driven by climate change should not 

cause any country to lose its statehood or its 

membership in the United Nations, and that sea-level 

rise should not diminish the maritime zones on 

which island nations and other coastal states rely for 

food and security.

xxxviii

● The United States will work with Pacific Island States

toward the goal of lawfully establishing and 

maintaining baselines and maritime zone limits, and will not challenge such baselines and maritime zone limits 

that are not subsequently updated despite sea-level rise caused by climate change.xxxix

● The United States has urged other countries to adopt similar approaches in order to safeguard vulnerable island 

States and promote regional stability.xl

● USINDOPACOM is focused on improving surveillance, enforcement, and the capacity of allies and partners to 

prevent foreign actors from exploiting their maritime entitlements. Efforts include: 

o U.S. military and Coast Guard subject matter expert exchanges with coastal States across the Indo-Pacific

aimed at developing legal frameworks and enforcement capabilities within coastal state EEZs; 

o Bilateral shiprider agreements with partners such as Papua New Guinea, Palau, and the Federated States 

of Micronesia, which allow the United States to conduct fishing vessel boardings within these countries’ 

EEZs; 

o The Oceania Maritime Security Initiative, a cooperative effort between the U.S. Department of Defense, 

the U.S. Coast Guard, and National Oceanic and Atmospheric Administration, to improve maritime 

domain awareness and EEZ security across the Pacific Ocean;xli

o The informal Partners in the Blue Pacific initiative (involving Australia, Japan, New Zealand, the United 

Kingdom, and the United States) that includes a commitment to addressing the challenges of IUU fishing

and maintaining MDA through cooperative partnerships across the region;xlii and 

o The Quad’s (Australia, India, Japan and the United States) Indo-Pacific Partnership for Maritime Domain 

Awareness, which uses tools such as commercial satellite radio frequency data collection to provide realtime information to coastal States on activities occurring within their maritime zones.

xliii

PROPOSED COUNTER-LAWFARE APPROACH

** This section offers suggested language for incorporation into communications strategies **

● Sea-level rise due to climate change threatens coastal States worldwide and poses an existential threat to Pacific 

Island States. 

● USINDOPACOM recognizes the severity of this threat and is committed to working with allies and partners to 

promote stability, security, certainty, and predictability of maritime entitlements that are vulnerable to sea-level rise.

● Without action by the international community, the sovereign rights and interests of coastal States will remain under 

threat and foreign actors could exploit ambiguity in maritime entitlements to their benefit and to the detriment of 

coastal States. 

● Addressing sea-level rise with an approach based in the rule of law supports preservation of maritime zones and helps 

ensure stability, security, certainty, and predictability. 

● UNCLOS does not exclude an approach based on the preservation of baselines and outer limits of maritime 

zones in the face of climate change-related sea-level rise. 

● The international community should support the Pacific Islands Forum’s landmark Declaration on Preserving 

Maritime Zones in the Face of Climate Change-related Sea-Level Rise. 

The crew of USCGC Oliver Henry conducts an approach in support of the 

Pacific Islands Forum Fisheries Agency's Operation 365 and Operation 

Rematau to stop IUU fishing, April 2023. Image source: USINDOPACOM. 
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● Some nations, including the PRC and Russia, have expressed caution regarding the preservation of maritime 

zones.

● Sea-level rise driven by climate change should not diminish the maritime zones on which island States and other 

coastal States rely upon for food, livelihoods, and security. 

● Upholding the rule of law in the Indo-Pacific requires the stability of maritime boundary delimitation agreements

as well as respect for the decisions of international courts and tribunals. 

● Pacific Island States are especially vulnerable to 

sea-level rise and need support from the 

international community to ensure their maritime 

zones are preserved in accordance with 

international law. 

● USINDOPACOM steadfastly supports Pacific 

Island States, to include the Freely Associated

States with whom the United States maintains a 

unique relationship and obligations under the 

Compacts of Free Association. 

● Consistent with U.S. policy, USINDOPACOM is 

committed to preserving the legitimacy of 

maritime zones, and associated rights and 

entitlements, that have been established 

consistent with UNCLOS and that are not subsequently updated despite sea-level rise caused by climate change.

● Consistent with U.S. policy, USINDOPACOM strongly supports initiatives by Pacific Island States to lawfully 

establish and maintain baselines and maritime zone limits in the face of sea-level rise caused by climate change.

● Raising awareness of the threat posed by sea-level rise to Pacific Island States and other coastal States may create 

opportunities for cooperation to preserve the rights of allies and partners across the Indo-Pacific region.

● USINDOPACOM supports and defends a Free and Open Indo-Pacific, stands with allies and partners in 

recognizing the danger of sea-level rise, and supports actions by Pacific Island States to preserve their sovereign 

rights.

● USINDOPACOM will work alongside other U.S. Federal entities and with allies and partners to protect 

sovereignty, promote adherence to international law, and uphold the rules-based international order.

i See U.N. International Law Commission, Sea-level rise in relation to international law, U.N. Doc. A/CN 4/761 (Feb. 2023), at 5-7,

https://legal.un.org/docs/?symbol=A/CN.4/761. This U.N. continues to study this issue and is seeking to finalize a substantive report on sea-level rise in 2025. Report 

of the Int’l Law Comm’n, U.N. Doc. A/78/10 (Nov. 2023), at 106. 

ii

 U.S. Department of State, Office of Ocean and Polar Affairs, U.S. Policy on Sea-level Rise and Maritime Zones, https://www.state.gov/marine-environment/. 

iii Id.

iv

 Id.

v U.N. International Law Commission, supra note i, at 75 (noting that “equity, as a method under international law for achieving justice, should be applied in favour of 

the preservation of existing maritime entitlements, the loss of which would result in catastrophic consequences for the most vulnerable States.”)

vi See, e.g., U.S.-Pacific Islands Forum Leaders Statement on Reaffirming U.S.-Pacific Partnership (Sep. 25, 2023), https://www.whitehouse.gov/briefingroom/statements-releases/2023/09/25/u-s-pacific-islands-forum-leaders-statement-on-reaffirming-u-s-pacific-partnership/; FACT SHEET: Enhancing the U.S.-Pacific 

Islands Partnership (Sep. 25, 2023), https://www.whitehouse.gov/briefing-room/statements-releases/2023/09/25/fact-sheet-enhancing-the-u-s-pacific-islandspartnership/; Congressional Research Service. The Compacts of Free Association, (Nov. 13, 1992), https://crsreports.congress.gov/product/pdf/IF/IF12194.

vii Lindsey, Rebecca, Climate Change: Global Sea Level, NOAA Climate, (Apr. 19, 2022), https://www.climate.gov/news-features/understanding-climate/climatechange-global-sea-level. 

viii Id. See also Caron, David D., Climate Change, Sea Level Rise and the Coming Uncertainty in Oceanic Boundaries: A Proposal to Avoid Conflict (October 6, 2014) in 

MARITIME BOUNDARY DISPUTES, SETTLEMENT PROCESSES, AND THE LAW OF THE SEA 1-17, https://ssrn.com/abstract=2506092, which notes a consensus estimate 

of sea-level rise by 2100 of between 1.5 and three feet. 

ix NASA-UN Partnership Gauges Sea Level Threat to Tuvalu. 15 August 2023. https://sealevel.nasa.gov/news/265/nasa-un-partnership-gauges-sea-level-threat-totuvalu/.

x See United Nations Convention on the Law of the Sea (Dec. 10, 1982), 1833 U.N.T.S. 397 [hereinafter UNCLOS], Section 2. See also U.S. Commander’s Handbook on 

the Law of Naval Operations (NWP 1-14) [hereinafter NWP 1-14], section 1.4.

xi See, e.g., UNCLOS Art. 7 through Art. 14 discussing special rules for features such as deeply indented coastlines, island fringes along the coast, and bays. See also

NWP 1-14, section 1.4. 

xii

 UNCLOS, Art. 5.

 

Admiral Aquilino, Commander of USINDOPACOM, poses with Pacific Island 

leaders from Fiji, Nauru, and Tuvalu at USINDOPACOM’s International Military 

Law and Operations Conference, August 2023. Photo by MCC Shannon Smith. 
6 | Page

 

xiii UNCLOS, Art. 87. NWP 1-14, section 2.6. 

xiv UNCLOS, Art. 8. NWP 1-14, section 1.5.1. 

xv

 UNCLOS, Art. 3. NWP 1-14 section 1.5.2.

xvi UNCLOS, Art. 47. NWP 1-14, section 1.5.4. An archipelagic State is a State that is constituted wholly of one or more groups of islands. Such States may draw 

straight archipelagic baselines joining the outermost points of their outermost islands, provided that the ratio of water to land within the baselines is between 1:1 

and 9:1.

xvii UNCLOS, Art. 53. NWP 1-14, section 1.5.4. Note that this provision is accomplished either by the archipelagic state designating sea lanes and air routes, or, in the 

absence of such designation, by the use of routes which have been normally used for international navigation. 

xviii UNCLOS, Art. 33. NWP 1-14, section 1.6.1.

xix UNCLOS, Art. 56. NWP 1-14, section 1.6.2.

xx UNCLOS, Art. 87. NWP 1-14, section 1.6.3. 

xxi

 UNCLOS, Art. 121. NWP 1-14, section 1.5.3.1

xxii Id. 

xxiii

 Id.

xxiv

 Id.

xxv See, e.g., NASA-UN Partnership Gauges Sea Level Threat to Tuvalu. 15 August 2023. https://sealevel.nasa.gov/news/265/nasa-un-partnership-gauges-sea-levelthreat-to-tuvalu/.

xxvi For a dashboard of current maritime boundary delimitation agreements in the Indo-Pacific, see the Pacific Data Boundaries Dashboard at

https://pacificdata.org/dashboard/maritime-boundaries. For an example of a U.S. maritime boundary delimitation agreement in the Indo-Pacific, see Treaty Doc. 

114-13, The Treaties with the Republic of Kiribati and the Government of the Federated States of Micronesia on the Delimitation of Maritime Boundaries (2024), 

https://www.congress.gov/114/cdoc/tdoc13/CDOC-114tdoc13.pdf/. 

xxvii There are two areas, deltas and continental shelves, where UNCLOS does explicitly allow for permanent, fixed baselines despite future movement or erosion. 

UNCLOS, Art. 7(2) and Art. 76(9). This can be used to argue that, where the possibility of movement or regression was explicitly considered, the drafters of UNCLOS 

took a position advocating stability and predictability. For a more detailed analysis, see Caron, David D., Climate Change, Sea Level Rise and the Coming Uncertainty in 

Oceanic Boundaries: A Proposal to Avoid Conflict (October 6, 2014) in MARITIME BOUNDARY DISPUTES, SETTLEMENT PROCESSES, AND THE LAW OF THE SEA 1-17,

https://ssrn.com/abstract=2506092. 

xxviii Bangladesh v India, PCA Case No. 2010-16, Award, (Perm. Ct. Arb. July 7, 2914) at 216-217.

xxix ILA,Resolution 5/2018: Committee on International Law and Sea Level Rise, available at: https://www.ila-hq.org/en_GB/documents/conference-resolutionsydney-2018-english-2. This position was reiterated by the ILA’s Committee on International Law and Sea Level Rise in 2022. International Law Association, 

International Law and Sea Level Rise Report (Lisbon, June 2022), available at https://www.ila-hq.org/en_GB/documents/2022-report-ila-committee-june-2022.

xxx Pacific Island Forum, Declaration on Preserving Maritime Zones in the Face of Climate Change-related Sea-Level Rise, (Aug. 6, 2021), 

https://www.forumsec.org/2021/08/11/declaration-on-preserving-maritime-zones-in-the-face-of-climate-change-related-sea-level-rise.

xxxi Id.

xxxii U.N. International Law Commission, supra note i, at 11-30. In July 2023, the US reiterated its position to the U.N. on Sea-level rise and maritime zones. 

Submission from the United States of America to the International Law Commission on the topic “Sea-level rise in relation to international law” concerning the 

subtopics of statehood and protection of persons affected by sea-level rise (Jul. 2023). 

xxxiii Wendbourg, Mara, “Interpreting the Law of the Sea in the Context of Sea-Level Rise: The Ambulatory Thesis and State Practice”, Journal of Environmental Law, 

2023, 35, 499–507, 16 August 2023, https://doi.org/10.1093/jel/eqad024.

xxxiv Id. 

xxxv U.N. International Law Commission, supra note i, at 40.

xxxvi Id.

xxxvii U.S. Department of State, supra note ii. 

xxxviii FACT SHEET: Enhancing the U.S.-Pacific Islands Partnership (Sep. 25, 2023), https://www.whitehouse.gov/briefing-room/statements-releases/2023/09/25/factsheet-enhancing-the-u-s-pacific-islands-partnership/.

xxxix U.S. Department of State, supra note ii. 

xl

 Id.

xli See Coast Guard, Navy Begin High Seas Oceania Maritime Security Initiative Patrol (Apr. 6, 2022), https://www.pacom.mil/Media/News/News-ArticleView/Article/2991615/coast-guard-navy-begin-high-seas-oceania-maritime-security-initiative-patrol/.

xlii U.S. Department of State (DoS) Press Statement, Strengthening Shared Understanding Among the Partners in the Blue Pacific and Pacific Islands: Illegal, 

Unreported and Unregulated Fishing (IUUF) and Maritime Domain Awareness, 27 Jan 2023, available at https://www.state.gov/strengthening-shared-understandingamong-the-partners-in-the-blue-pacific-and-pacific-islands-illegal-unreported-and-unregulated-fishing-iuuf-and-maritime-domain-awareness-mda/.

xliii FACT SHEET: Quad Leaders’ Tokyo Summit 2022 (May 23, 2022), https://www.whitehouse.gov/briefing-room/statements-releases/2022/05/23/fact-sheet-quadleaders-tokyo-summit-2022/.