Countries are being “held hostage” by their reliance on fossil fuels, a former UN climate chief has warned, describing the health impacts of climate change as “the mother of all injustices”.

Christiana Figueres, an international climate negotiator who helped deliver the Paris agreement signed in 2016, made the comments as she was announced on Wednesday as co-chair of a Lancet Commission examining how sea-level rise is reshaping health, wellbeing and inequality.

Lancet Commissions are international collaborations that analyse major global health issues and influence policy. This commission will examine legal frameworks to hold countries accountable for the health harms of sea-level rise. It will report by September 2027.

While the timing of the announcement – amid the US-Israel war on Iran – is coincidental, Figueres said the fuel crisis was “dramatic proof” of the global dependence on fossil fuels that is driving geopolitical instability and the health impacts the commission will examine.

The commission comes after Pacific island health ministers called for greater global focus on sea-level rise as a health and justice issue, as well as an environmental challenge.

Rising seas contaminate drinking water, damage food supplies and force entire communities from their homes.

Sea-level rise is not uniform and is influenced by weather patterns, ocean currents and changes in gravity as ice sheets melt. The rise is larger in the oceans furthest from the ice sheets, and is higher than global averages in the Pacific. It means island nations including Tuvalu, Kiribati and Fiji may become uninhabitable within decades.

Many low-lying cities are also under threat, including New Orleans in the US, Cardiff and London in the UK, and Amsterdam in the Netherlands.

In March, research published in the international science journal Nature found that ocean levels had been underestimated due to inaccurate modelling. In some areas of the global south, including south-east Asia and the Indo-Pacific, they may be 100cm to 150cm higher than previously thought.

“We in the climate community are very guilty of explaining things in way too esoteric terms, as though climate change were something that is not happening now,” Figueres said.

“So framing these issues in terms of health, in terms of dignity, in terms of livelihoods, in terms of identity and cultural continuity … provides a much better context to the challenge of reducing emissions, because we then understand that this really is about the human experience on this planet …

“Just from a health perspective, it is now affecting drinking water, it’s affecting sanitation, it’s affecting food security because of the salinisation of all of these lands that are ocean front.

“It is happening now, it is a crisis of health and it is the mother of all injustices.”

Figueres said the commission would consider the intergenerational trauma and inequity caused by displacement.

“Can you imagine the pain of having to leave the bones of ancestors and being displaced in order to be able to protect the future of children?” she said.

“That is a pain that is already being experienced in the Pacific islands. That is a pain that we cannot put in economic terms. The grief is huge.”

She said young people were “growing up understanding that they are in a world that is already ravaged by climate change”.

“How many of them don’t even want to have children because they’re so concerned about the conditions under which those children might have to grow up and live?”

The commission will consider how to hold some of the biggest polluters to account for the irreversible harm being caused to countries contributing the least to climate change. It will assess existing legal instruments, identify gaps in protections and consider new ways to safeguard health and uphold justice for suffering communities.

A landmark advisory opinion published in 2025 by the international court of justice (ICJ) found that countries have a legal obligation prevent harm to the climate, and that failing to do so could result in them paying compensation and making other forms of restitution.

Though non-binding, Figueres said the finding would boost the number of climate litigation cases and lead to groundbreaking claims.

“Just the fact that the ICJ came out with an unequivocal opinion is already a crucial first step in terms of legal consequences,” she said.

Vanuatu will in May lead a UN general assembly resolution to uphold the ICJ opinion, which if passed would help shape how the findings were implemented globally.

But UN experts have warned of attempts by some states to block the resolution from even being considered, and of growing resistance to explicit references to fossil fuels and legal responsibility for climate harm.

Figueres said legally binding agreements were not enough to tackle the health harms of the climate crisis, recalling how Canada exited the Kyoto agreement just before facing billions in penalties for failing to meet its emissions targets.

“They simply sent me a letter and said, ‘Madam executive secretary, hereby, Canada removes itself from the Kyoto protocol.’ So having a legally binding agreement does not guarantee at all that any country would comply.”

She said she believed change was more likely to come from a combination of legal pressure, scientific evidence and what she described as appealing to the “enlightened self-interest” of governments and corporations.

“That is why it is important to to lay bare the consequences of inaction,” Figueres said, adding: “Companies should understand for their business continuation, they should reduce emissions. Governments should understand that in order for them to stabilise their economy, and protect their people, they should reduce emissions.

“I just think that enlightened self-interest based on scientific facts – which is what the commission is going to put forward – is a much more effective route to emission reductions than a legally binding agreement from which anybody can withdraw.”