The world has broken the 1.5°C promise it made to its most vulnerable countries. The breach has not yet been recorded on a sustained basis, but the United Nations Environment Programme (UNEP) says it is widely assessed as unavoidable and likely within the next few years. Even its most optimistic scenario puts peak warming at 1.8°C. For small states that fought to secure recognition of 1.5°C in the Paris Agreement, this confirms the failure to deliver a safeguard on which their security, economies and, in some cases, survival depend.
Small and climate-vulnerable states contributed negligibly to the greenhouse gas emissions that created this crisis, yet they are already borrowing heavily to repair its damage. If the major emitting countries have failed to prevent the world from breaching 1.5°C, those least responsible should not incur more debt to pay for the consequences.
When the Paris Agreement was concluded in 2015, small island developing states fought hard for recognition of 1.5°C because the difference between 1.5°C and 2°C was understood to be a matter of life or death. Every additional fraction of a degree increases the risks from sea-level rise, extreme weather, ecosystem damage and loss of habitable land.
I wrote at the time that the Agreement would ultimately be judged on whether warming was held to no more than 1.5°C and whether industrialised countries provided adequate financing for mitigation and adaptation. Eleven years later, the first objective is slipping away, while the second remains far below what vulnerable countries require.
However, the European Union and its member states deserve recognition as the largest providers of international public climate finance, contributing pound 31.7 billion from public sources in 2024 and mobilising a further pound 11 billion privately. But even this comparatively greater effort falls short of the needs confronting vulnerable states.
UNEP now speaks of an ‘overshoot’, in which temperatures exceed 1.5°C before later efforts seek to bring them down. But damage incurred during an overshoot cannot simply be reversed. Infrastructure must be rebuilt, displaced communities resettled and public debt accumulated after climate disasters repaid.
This is where climate vulnerability becomes a debt problem.
When a hurricane destroys roads, schools, hospitals, electricity systems and homes, governments must rebuild. If grants and highly concessional financing are unavailable, they borrow. Climate destruction produces debt, while debt service reduces the resources available for resilience and development.
Hurricane Maria demonstrates the scale of the danger. The damage and losses it caused in Dominica in 2017 amounted to approximately 226 per cent of the country’s 2016 gross domestic product. Few economies could absorb destruction on that scale without lasting financial consequences.
The international financial system compounds the problem. Many Small Island Developing States are excluded from concessional financing because per capita income supposedly makes them too wealthy to qualify, even though one hurricane can destroy assets and economic output accumulated over many years. A country can therefore be classified as too prosperous for concessional development finance while remaining vulnerable to losing much of its economy overnight.
The injustice is obvious. Vulnerable governments nevertheless have obligations of their own. They must enforce stronger building standards, improve water management, protect coastlines, expand renewable energy and invest seriously in disaster preparedness. But those responsibilities do not erase the unequal origins of the crisis or enable small economies to finance repeated reconstruction without outside support.
The accounting is incomplete in another respect. A 2026 systematic review of 263 scientific studies and 36 reports notes estimates that military activity accounts for approximately 5.5 per cent of global greenhouse gas emissions. Treated as a country, the world’s militaries would rank collectively as approximately the fourth-largest emitter. Yet less than one-tenth of military and conflict-related emissions is captured in existing international reporting.
An analysis by researchers at Queen Mary University of London, Lancaster University and the Climate and Community Institute estimated that the first 14 days of the 2026 war involving the United States, Israel and Iran produced more than five million tonnes of carbon dioxide equivalent. Whatever the security arguments, these emissions enter the same atmosphere and contribute to consequences borne by states far removed from the conflict.
There is now also an important legal dimension.
In 2024, the International Tribunal for the Law of the Sea concluded that anthropogenic greenhouse gas emissions constitute pollution of the marine environment under the United Nations Convention on the Law of the Sea.
In July 2025, the International Court of Justice confirmed that states have obligations under international law to protect the climate system from significant harm. It also recognised that breaches may engage the established principles of state responsibility and reparation where the necessary legal conditions are satisfied.
These advisory opinions do not automatically produce compensation. Questions of causation, attribution and quantification remain. But climate commitments are now reinforced by authoritative findings concerning the legal obligations and potential responsibility of states.
The international financial response should reflect that reality.
Climate adaptation and reconstruction in highly vulnerable small economies should be financed primarily through grants and deeply concessional resources, not commercial borrowing.
Debt clauses that automatically suspend repayments after major climate-related disasters should become standard. The Multidimensional Vulnerability Index should be used throughout international financial institutions so that access to concessional finance reflects exposure to shocks rather than relying principally on per capita income.
The Fund for Responding to Loss and Damage must receive resources proportionate to the problem it was created to address. Debt relief or restructuring should also be considered where sovereign debt has been substantially increased by repeated climate disasters.
These measures are reasonable responses to unequal responsibility for a global problem and the unequal burden of its consequences. No one should regard them as charity.
The principle should be straightforward: no vulnerable country should become more indebted because it must repeatedly rebuild from damage caused substantially by a global problem for which it bears negligible responsibility.
Crossing 1.5°C does not mean that further climate action is pointless. It underscores the imperative for remedial and preventive action. Major emitters must accelerate reductions in greenhouse gases, while all countries, including small states, must do what they can to build resilience.
But the latest assessment changes the terms of the discussion.
For years, vulnerable states were asked to trust that emissions would fall sufficiently, climate finance would increase and 1.5°C could be protected. That confidence has not been justified.
Small states must accept responsibility for what they can and should do themselves. But they should not quietly accept a financial system in which they must borrow heavily to pay for the consequences of a crisis they did little to create.
The world is failing to keep the 1.5°C safeguard. Small states should not be required to pay the bill.