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In a new report, the rating agency said alongside the effects on societies of their ageing populations, the impact of climate change, specifically global warming, would put downward pressure on sovereign ratings.
In the ranking, all the 20 most vulnerable nations were emerging markets and many of them were in Asia-Pacific. Vietnam, Bangladesh, Fiji, the Philippines, Papua New Guinea and Indonesia were among the list of nations in the bottom 10 places.
Their vulnerability was in part due to their reliance on agricultural production and employment - which could be vulnerable to shifting climate patterns and extreme weather events - but also due to their weaker capacity to absorb the financial cost, report author Moritz Kraemer and S&P's chief sovereign credit risk officer said.
Key points from the report included climate change being one of the global mega-trends to affect sovereign creditworthiness, in most cases negatively.
The impact on creditworthiness would probably be felt through various channels, including economic growth, external performance and public finances.
''Sovereigns will probably be unevenly affected by climate change, with poorer and lower rated sovereigns typically hardest hit, which could contribute to rising global rating inequality.''
The report said extreme weather events, such as tropical storms or floods, seemed to have been on the rise since the early 1980s.
Data collected by MunichRe, a reinsurer, suggested weather-related loss events had risen in all continents, but most significantly in Asia and North America where they had increased more than fourfold.
In Eastern Asia, overall losses - insured and non-insured - used to be below $US10 billion ($NZ11.6 billion) a year but had regularly surpassed $US20 billion during the past decade, with a peak of more than $US50 billion, Mr Kraemer said.
''Typhoon Haiyan hitting the Philippines in November 2013 has been a powerful and hugely destructive reminder of this trend.''
Typhoon Haiyan killed more than 6200 people and left tens of thousands homeless when it struck.
So far, S&P had not revised the rating of a sovereign as a consequence of an extreme weather event.
''We have taken the view that the size of the devastation, while large in absolute terms, has not been sufficient to impact a rating overall. However, assuming that extreme weather events are on the rise in terms of frequency and destruction, how this trend could feed through to our ratings on sovereign states bears consideration,'' Mr Kraemer said.
To measure the degree to which economies were exposed to the risks, S&P had created a composite of three different variables and arrived at a vulnerability ranking for the 116 sovereigns it rated.
The three variables were: share of the population living in coastal areas below 5m of altitude; share of agriculture in national GDP; the vulnerability index compiled by Notre Dame University Global Adaptation Index which measured the degree to which a system was susceptible to, and unable to cope with, adverse effects of climate change.
In the ranking, Luxembourg, Switzerland and Austria were at the top of the least-vulnerable list.
Credit risk from climate change
Vietnam, Bangladesh, Fiji, Philippines, Papua New Guinea and Indonesia among nations in the bottom 10 places.
Luxembourg, Switzerland and Austria.