How low-lying is the Marshall Islands and how much of it is at risk from rising seas?

With an average elevation of just seven feet above sea level, the Republic of the Marshall Islands is acutely vulnerable to inundation from both episodic events such as storm surge and chronic conditions such as sea-level rise. Seven feet sounds like something you could stand in, until you remember that a storm surge or king tide doesn't need to overtop you permanently to destroy a freshwater lens, flood a hospital or salt a crop field.

The Marshall Islands is a string of atolls in the central Pacific Ocean and consists of 29 atolls, with sea levels rising at twice the global average rate. An atoll is a ring-shaped coral reef that barely clears the surface of the ocean, enclosing a lagoon. It is not a volcanic island with a mountain at its center. It is essentially a thin strip of coral sand sitting in open water.

What is at risk

The atolls of the Marshall Islands are some of the most at-risk areas in the world as sea level continues to rise.

The numbers from the capital tell the story plainly. A World Bank study found that rising sea levels are projected to endanger 40 percent of existing buildings in the capital, Majuro, with 96 percent of the city at risk of frequent flooding induced by climate change. That is not some distant scenario: already, residents are facing extreme high tides and 16-foot swells that flood the islands with saltwater, damaging homes and infrastructure and contaminating the freshwater supply.

The risk scales sharply with every centimeter gained. A 1-meter sea level rise will mean 40 percent of the buildings in Majuro would be permanently inundated, and entire islands will disappear, according to a study by the Marshall Islands government and the World Bank. In Ebeye, the risk is even higher, with 50 percent of buildings being permanently flooded under the same scenario. With a 2-meter sea level rise, all the buildings of Majuro will be permanently flooded or at high risk of flooding.

Some projections estimate that future sea-level rise could exceed the average elevation of these islands by 2100. When the sea exceeds your highest point, there is no higher ground to retreat to.

The threat that arrives before the flooding

Research suggests the loss of freshwater resources could make the islands uninhabitable long before they might sink below the ocean waves. Saltwater infiltrating the underground freshwater lens, the thin bubble of fresh water beneath each island, is a slower but equally decisive threat. You don't need the island to disappear to make it unlivable. You just need the water to go bad.

This is the existential arithmetic behind President Hilda Heine of the Marshall Islands pressing for the Loss and Damage Fund at the 81st UN General Assembly. The country emits almost nothing, sits on nothing tall enough to save it, and is already paying the price.