Why a new ruling on the law of the sea and climate change matters for Australia and especially our island neighbours

The International Tribunal for the Law of the Sea has found countries are obliged to protect the oceans from climate change impacts under the law of the sea.

The tribunal’s 21 judges issued a unanimous Advisory Opinion on Climate Change and International Law on May 21. It’s a landmark decision. For the first time an international court or tribunal has laid out the extent of state obligations to mitigate climate change under the United Nations Convention on the Law of the Sea.

These findings are significant because ocean and climate are fundamentally linked. The global ocean covers 72% of Earth’s surface and holds 98% of its water. The advisory opinion cited the Intergovernmental Panel on Climate Change (IPCC) 2019 finding that the ocean had taken up 90% of the excess heat in the climate system.

This ruling is important for Australia, which has sovereign rights over an area of ocean – its maritime jurisdiction – almost 50% larger than its land area (excluding Antarctica).

The ruling is vitally important for small island (but large ocean) states that are most threatened by climate change impacts on the oceans.

A matter of survival for some states

Climate change impacts include ocean warming, coral bleaching, acidification and sea-level rise. These are existential threats for some island nations.

For example, Tuvalu in the South Pacific consists of nine low-lying atolls and 101 reef islands. Their combined land area is 26 square kilometres. Crucially, the average height above sea level is less than 3 metres.

This vulnerability to rising sea levels is only part of the problem for Tuvalu. The increased frequency and intensity of extreme weather events due to climate change compounds the threat.

In 2015 Cyclone Pam created storm waves that displaced 45% of Tuvalu’s people. Loss and damage costs were estimated at US$10 million. That was more than a third of Tuvalu’s GDP at the time.

In response to these grave challenges, Antigua, Barbuda and Tuvalu founded the Commission of Small Island States on Climate Change and International Law (COSIS) in October 2021, on the eve of the COP26 UN climate conference. Members now include Palau, Niue, Vanuatu, St Lucia, St Vincent and the Grenadines, St Kitts and Nevis, and the Bahamas.

Tribunal lays out specific obligations

A key finding was the tribunal’s recognition that greenhouse gas emissions constitute pollution of the marine environment under the convention.

The tribunal also determined that parties to the convention have substantive, specific obligations to mitigate the impacts on the oceans resulting from their greenhouse gas emissions. This applies to both the high seas and maritime areas under a state’s jurisdiction. These measures include laws and regulations to prevent, reduce and control marine pollution due to emissions from:

• land-based sources
• vessels flying their flag or under their registry
• offshore activities such as oil and gas extraction.

State parties must also take all measures needed to implement the international standards set by competent international organisations, including the International Maritime Organization (IMO) and International Civil Aviation Organization (ICAO).

States are required to act on the basis of best available science and international rules and standards. The tribunal underscored the relevance of the UN Framework Convention on Climate Change and the Paris Agreement, with its goal of limiting the global temperature increase to 1.5°C above pre-industrial levels, as the main international legal instruments to combat climate change.

These obligations are recognised as being ones of conduct (to make all necessary efforts) rather than ones of result (ensuring harm does not occur). The tribunal made it clear that the standard of due diligence in relation to meeting these obligations is “stringent”.

The advisory opinion noted efforts to fulfil these obligations may vary with the means available to states. It acknowledged the principle of “common but differentiated responsibilities”, which has been developed under the climate regime.

Law of the sea obligations to assist developing states, especially those vulnerable to climate change, were also highlighted. So too was the requirement to monitor and assess climate impacts and share information.

The tribunal emphasised the specific obligation on states to prevent emissions under their control from causing damage to the marine environment of other states. It pointed to specific convention obligations of co-operation and consultation between states or through international organisations.

The tribunal recognised the obligation to protect and preserve the marine environment was broad in scope. However, it stressed the specific obligations to protect and preserve rare and fragile ecosystem, the habitats of threatened or endangered species, and living marine resources threatened by climate change impacts.

Advisory opinions carry weight

While it’s an advisory opinion, the tribunal’s findings are authoritative.

Previous advisory opinions have made important contributions to the law. For example, the tribunal’s decisions on deep-seabed mining and illegal fishing in waters under the jurisdiction of states developed the concept of due diligence as a standard of care under the law of the sea.

An advisory opinion issued by the International Court of Justice persuaded the UK to resume negotiations with Mauritius over the future return of the Chagos islands. It also enabled the tribunal to resolve a maritime boundary dispute between the Maldives and Mauritius.

This week’s advisory opinion underpins efforts by vulnerable developing states, including small island states, which have contributed the least to climate change, to hold the developed world to account.

Under the law of the sea, states bear responsibility for failing to comply with obligations to prevent pollution and protect the marine environment. The tribunal has confirmed these obligations apply to climate change and ocean acidification.

Its advisory opinion could open the door to future litigation of climate change issues related to the oceans, including through the convention’s compulsory dispute resolution mechanisms.