The top United Nations court will take up the largest case in its history when it opens two weeks of hearings into what countries worldwide are legally required to do to combat climate change and help vulnerable nations.

After years of lobbying by island nations who fear they could simply disappear under rising sea waters, the UN General Assembly asked the International Court of Justice last year for an opinion on “the obligations of States in respect of climate change.”

“We want the court to confirm that the conduct that has wrecked the climate is unlawful,” Margaretha Wewerinke-Singh, who is leading the legal team for the Pacific island nation of Vanuatu, said.

In the decade up to 2023, sea levels have risen by a global average of around 1.7 inches, with parts of the Pacific rising higher still. The world has also warmed 1.3C since pre-industrial times because of the burning of fossil fuels.

Vanuatu is one of a group of small states pushing for international legal intervention in the climate crisis.

“We live on the front lines of climate change impact. We are witnesses to the destruction of our lands, our livelihoods, our culture and our human rights,” Vanuatu’s climate change envoy Ralph Regenvanu told reporters ahead of the hearing.

Any decision by the court would be non-binding advice and unable to directly force wealthy nations into action to help struggling countries.

Yet, it would be more than just a powerful symbol since it could serve as the basis for other legal actions, including domestic lawsuits.

On Sunday, ahead of the hearing, advocacy groups will bring together environmental organisations from around the world.

Pacific Islands Students Fighting Climate Change — who first developed the idea of requesting an advisory opinion — together with World Youth for Climate Justice plan an afternoon of speeches, music and discussions.

From Monday, the Hague court will hear from 99 countries and more than a dozen intergovernmental organisations over two weeks.

It is the largest line-up in the institution’s nearly 80-year history.

Last month at the United Nations’ annual climate meeting, countries cobbled together an agreement on how rich countries can support poor countries in the face of climate disasters.

Wealthy countries have agreed to pool together at least 300 billion dollars (£235 billion) a year by 2035 but the total is short of the 1.3 trillion dollars (£1 trillion) that experts and threatened nations, said is needed.

“For our generation and for the Pacific Islands, the climate crisis is an existential threat. It is a matter of survival, and the world’s biggest economies are not taking this crisis seriously. We need the ICJ to protect the rights of people at the front lines,” Vishal Prasad, of Pacific Islands Students Fighting Climate Change, told reporters in a briefing.

Fifteen judges from around the world will seek to answer two questions: What are countries obliged to do under international law to protect the climate and environment from human-caused greenhouse gas emissions? And what are the legal consequences for governments where their acts, or lack of action, have significantly harmed the climate and environment?

The second question makes particular reference to “small island developing States” likely to be hardest hit by climate change and to “members of “the present and future generations affected by the adverse effects of climate change.”

The judges were even briefed on the science behind rising global temperatures by the UN’s climate change body, the Intergovernmental Panel on Climate Change, ahead of the hearings.

The case at the ICJ follows several rulings around the world ordering governments to do more to reduce greenhouse gas emissions.