UN secretary-general warns of impact of sea level rise, could cause 'mass exodus' of populations

Billions of people are at "unthinkable" risk because of rising sea levels, according to the United Nations.

Speaking at the United Nation's Security Council meeting on Tuesday, U.N. Secretary-General António Guterres said the coastlines of some countries have already seen sea levels rise at triple the average rate.

"The impact of rising seas is already creating new sources of instability and conflict," he said.

As strong waves repeatedly crash against the shore, coastal erosion naturally occurs; however, as temperatures around the world increase and sea levels rise, the damage to the coast's natural barriers is being exacerbated with each ensuing monster storm with tropical force winds or higher -- which typically causes the most damaging events of erosion, according to environmental scientists.

Low-lying communities and entire countries could disappear in the next few decades because of rising sea levels, according to the U.N.

"We would witness a mass exodus of entire populations on a biblical scale, and we would see ever-fiercer competition for fresh water, land and other resources," Guterres said.

According to the secretary-general, rising sea levels would make it harder for people to access water, food and health care.

Global average sea levels have risen faster since the beginning of the 20th century than in any previous century in the last 3,000 years, according to new data released from the World Meteorological Organization.

Since 1993, the rate at which sea levels have risen has doubled, according to the WMO's provisional State of the Global Climate in 2022 report. Since January 2020, it's increased by nearly 10 mm, hitting a record high last year, according to the report.

The WMO said that while the increase is measured in millimeters, it can add up to 3.2 feet, or 1 meter, every century, bringing devastating threats to millions of people living along the coast.

Through the Paris Climate Agreement, world leaders set a goal to limit the earth's warming to 1.5 degrees Celsius, or 2.7 degrees Fahrenheit; however, according to WMO, even if that limit is reached, seawater levels would still significantly rise around the world.

"Our world is hurtling past the 1.5-degree warming limit that a livable future requires, and with present policies, is careening towards 2.8 degrees -- a death sentence for vulnerable countries," Guterres said.

Mega-cities on every continent, including cities like Lagos, Bangkok, Mumbai, Shanghai, London, Buenos Aires and New York will be impacted by sea level rise, he said.

"The danger is especially acute for nearly 900 million people who live in coastal zones at low elevations — that's 1 out of 10 people on earth," the secretary-general said.

Guterres has called for countries to step up their efforts to reduce emissions and to safeguard climate justice, particularly for developing nations that need resources to tackle climate disasters.

ABC News' Ellie Kaufman and Julia Jacobo contributed to this report.