The "Multidimensional Vulnerability Index" (MVI) is set to act as a complement to GDP and other development metrics.

Since the 1990s, small island developing states (SIDS) that are not poor enough in terms of GDP per capita to access low-interest development financing but nonetheless face vulnerability to external shocks like climate change have been calling for such a measure.

After years of international discussions to define the contours of the new tool, the General Assembly finally adopted a resolution by consensus on Tuesday that mandates the UN and a committee of independent experts keep it up to date.

Based on the findings of a UN high-level panel, it incorporates indicators linked to a state's structural vulnerabilities and lack of economic, environmental and social resilience.

These factors include import dependency, exposure to extreme weather events and pandemics, impacts of regional violence, refugees, demographic pressure, water and arable land resources and mortality of children under five.

Although initially proposed by small island states, the MVI "aims to capture exogenous vulnerabilities and lack of resilience to exogenous shocks of all developing countries, so as to ensure credibility and comparability," the resolution says.

The resolution notes that use of the index is voluntary, but calls on organs of the UN and multilateral development banks to consider using the new tool to complement existing policies.

In a statement, the Alliance of Small Island States (AOSIS) welcomed the passage of the resolution as a "monumental step forward."

"AOSIS holds no notion of a rose-tinted world. We know that the MVI will not strip away the system we know," said Fatumanava-o-Upolu III Dr Pa'olelei Luteru, Samoa's ambassador to the UN, who chairs the alliance.

"We wish to see the MVI deployed in real-world contexts, and through its testing and eventual refinement, that it will unlock a new way of thinking and acting on development," he said.