Full coverage: Paris Climate Agreement

Perhaps nowhere are the effects of climate change more drastically felt than among small island developing states, where rising sea levels are redefining coastlines and extreme weather is already forcing migration. As world leaders sign on to a historic climate treaty in New York, island populations are holding out hope that this united front might avert the worst. 

For island nations from the Caribbean to the Pacific to the Indian Ocean... the tides are already turning as global warming wreaks havoc; eroding coastlines, causing record tides and extreme weather events.

Many of them will be dealt a double-blow. A new study by the journal Nature Climate Change estimates up to 73 percent of island states, home to 16 million people - will face increasingly dry conditions by the middle of this century, even as rising sea levels are swallowing up their coastlines.

To avert disaster, island nations including the Maldives, Tuvalu, Kiribati, Vanuatu and the Marshall Islands, have signed on to the historic climate agreement.

While the most threatened, these are also the countries that emit the least greenhouse gases, which is why this Paris Agreement also encourages richer developed nations - the world's major emitters of greenhouse gases - to help the poorer and most vulnerable ones.

As part of the deal, richer developed nations will send $100 billion dollars a year to help developing states build climate resilience and put their countries and economies on a low-carbon path.

In a sign of eagerness to see its measures take effect, 13 small island nations are fully ratifying the Paris accord at the UN going beyond the signing ceremony to submit their action plans on how each of them will do their part.