Takehiko Nakao was speaking at a conference of officials from the four atoll nations (Kiribati, the Marshall Islands, Maldives and Tuvalu), experts and development partners last week.

Atolls are ring-shaped coral reefs that often formed above underwater mountains or extinct volcanoes.

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An atoll in the Maldives

Most are found in the Pacific Ocean, and are small territories of other sovereign nations, but they sometimes make up island nations themselves.

For example the Maldives, in the Indian Ocean, is a chain of 26 such atolls, and is the smallest Asian country by both land area (298km squared) and population (402,000 at the time of the 2014 census).

Nakao told the conference: “For the atoll nations, climate change is not a distant threat for a future generation to face but an immediate emergency, with tropical storms and rising seas taking their toll on human lives, livelihoods, and infrastructure.”

Although the world’s 57 small island developing states have been recognised for a long time as being vulnerable to the effects of climate change, atoll nations are in a “class of their own”, the ADB said.

Their land mass is thin, they have very little high ground and their elevation averages about 2m above sea level.

Projections show sea level could rise by as much as 2.5m by the end of the century.

Kiribati ambassador to the US Teburoro Tito told the conference: “We are the pancakes on the water.

“We are very low-lying, we are very much impacted by rising sea level, frequency of storm intensity breaking on our coastlines and disrupting the livelihoods of people.”

The ADB said it is working with atoll nations to help them develop ways to adapt to climate change and their own particular increased vulnerability to natural disasters.