Rising sea level isn’t just about losing a few inches of shoreline to the encroaching oceans each year. It’s a threat multiplier that will disrupt and destabilize global societies unless there is an organized international effort to get ahead of the problem, United Nations Secretary General António Guterres told the U.N. Security Council today in New York.

“Mega-cities on every continent will face serious impacts including Cairo, Lagos, Maputo, Bangkok, Dhaka, Jakarta, Mumbai, Shanghai, Copenhagen, London, Los Angeles, New York, Buenos Aires and Santiago,” Guterres said, as the security council met at the ministerial level for an debate on sea level rise and its implications for international peace and security.

Guterres said the danger is most acute for about 900 million living in low-lying coastal zones. That’s one out of 10 people on earth, and some coastlines have already seen triple the average rate of sea level rise. Some countries could disappear forever, he added.

“We would witness a mass exodus of entire populations on a biblical scale,” he said. “And we would see ever-fiercer competition for fresh water, land and other resources. The impact of rising seas is already creating new sources of instability and conflict.” 

Today’s security council debate was initiated by Malta, a small island nation strategically located between Africa and Europe in the central Mediterranean Sea. The island is a focal point for rescuing migrants from developing countries in the Global South, who are fleeing rising sea level and other climate impacts by trying to make dangerous boat crossings from Africa to Europe.

The United Nations refugee agency, UNHCR, estimates that about 21.5 million people have been displaced on average each year since 2008 by extreme weather and other climate impacts. The flow of refugees into Europe has triggered a social and political backlash that has strengthened right wing authoritarian parties, which could undermine international cooperation on various global risks, including global warming.

The warning from Guterres is well-supported by recent research and reports showing that the rate of sea level rise has doubled in the past few decades, up to about 1.7 inches per decade, with twice that amount in particularly vulnerable parts of the global south, including small island nations. 

Some research shows that ice loss is still on a pace that would lead to worst-case outcome, potentially with several feet of sea level rise by 2100. One recent study based on new satellite data shows that about twice as much land will be submerged by rising seas in the coming decades than previously believed because earlier estimates miscalculated the elevation of some coastal regions.

Related: New Federal Report Warns of Accelerating Impacts From Sea Level Rise

Security Council Needs to See the Climate-Security Nexus

Most—but not all—countries in the 15-member U.N. Security Council agree that climate change is a threat multiplier that needs to be addressed in the broader context of efforts to prevent conflict, sustain peace and build resilience in conflict-affected or otherwise fragile states.

But countries including Brazil, China and Russia have previously expressed concerns about having the security council engage directly on climate issues, according to the Security Council Report, a nonprofit group that serves as a security council watchdog and advocates for more transparency.

In the past, those countries have said climate change is mainly a sustainable development issue best addressed under the U.N.’s climate program. In a preview of today’s meeting, the watchdog group writes that it expects some countries to argue that the security council doesn’t have a mandate, or the expertise, to consider sea level rise.

“There has been a lot of resistance on the part of some security council members, most particularly Russia, China and in some circumstances, India, to divert attention away from talking about the security implications of climate change in the security council,” said Olivia Lazard, an expert of climate-related security issues with Carnegie Europe, a global nonprofit foreign policy think tank. Those countries, she said, claim the U.N. has other agencies tasked with covering the impacts of climate change, so there is no reason to discuss it at the heart of the U.N. system. 

“There is a concern that it plays into larger geopolitical considerations where some actors maybe are concerned that the topic of climate change would be used as a way to push other agendas,” she said. “So it’s a contentious conversation, which is usually quite polarizing.”

What Does Global Security Look Like in a Time of Climate Change?

Nevertheless, European states, in some cases supported by African countries, have tried to advance climate discussions in the context of global security, with the recognition that climate impacts fundamental drive insecurity, Lazard said.

Sea level is an interesting lever for that discussion because it gets at key topics like how global sovereignty is defined. 

“The very notion of security, the way that we understand it in the international community, is how to define means of governance over certain territorial boundaries,” she said. “So when we talk about sea level rise, we face a world where some countries or some parts of territory are disappearing.” Lazard said climate change was first discussed at the security council in 2007 at the urging of the United Kingdom, with subsequent discussions helping clarify “the ways climate change is fundamentally changing the physical distribution of natural resources, territorial boundaries, and therefore changing the way in which we can understand how we build a security system at a global level,” she added.

From a 15-year perspective, the shift in the global conversation is dramatic. 

“It’s super radical. And this is the reason why we’re also seeing conversations being so polarized within the Security Council,” she said. “The reality is that we have to have very specific technical conversations around sea level rise.” That means, she added, having detailed legalist and jurisdictional conversations about governance of things like maritime boundaries, which will change as the oceans change.

“What is going to be the shape of the security organization starting now and for the next 50 years,” she said. “That is the question that is being asked at the moment.”

Related: Rising Seas Are Flooding Norfolk Naval Base, and There’s No Plan to Fix It

Tough Questions, no Easy Answers

For Vanessa Frazier, Malta’s permanent U.N. representative, “the nexus between climate change and security is an established theme,” with scientific research showing that climate change impacts like sea level rise will worsen existing vulnerabilities and create new risks, Frazier wrote in a Feb. 2 letter that outlined the agenda for today’s security council debate. 

She noted that the threat of sea level rise is most clear in small island developing nations, where “the pressures on the world’s oceans threaten their very existence. Continued and accelerating sea level rise has the ability to disable critical infrastructure and subject low-lying coastal communities and entire island states to submergence and territorial loss.” 

She also said there is research showing that the humanitarian consequences disproportionately affect women and children “by further exacerbating instability in regions with already existing tensions over resources, such as food and water,” and called on the security council to grapple with that reality “in the changing global context of advancing the women and peace and security agenda.”

The key questions, she added, are, “How can the security council respond to the triple nexus of gender inequality, state fragility and climate vulnerability, and what actions can be identified to strengthen women’s leadership and inclusion in decision-making?”

Related: Leaders and Activists at COP27 Say the Gender Gap in Climate Action is Being Bridged Too Slowly

Tackling Climate Impacts Requires Systemic Changes

As the global body primarily responsible for maintaining international peace and security, Guterres said the security council needs to “meet the rising tide of insecurity with action across three areas.” 

“The Security Council has a critical role to play in building the political will required to address the devastating security challenges arising from rising seas,” he said. “First, we must address the root cause of rising seas, the climate crisis. 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,” he added, calling that “a death sentence” for vulnerable countries.

A wider understanding of the root causes of insecurity is also required, which means identifying and addressing a much wider range of factors, “from poverty, discrimination and inequality, to environmental disasters like rising sea levels,” he said. 

And he said the U.N. must address the impacts of rising seas in legal and human rights frameworks, including international refugee law to find “innovative legal and practical solutions to address forced human displacement and on the very existence of the land territory of some states,” he said. “People’s human rights do not disappear because their homes do.”

Areas the security council could help in the short-term include issues of continued statehood, despite loss of territory to sea level rise, as well as ceding territory to affected states or even establishing confederations of states for a more effective response—all themes that were explored by the International Law Commission, the U.N.’s legal arm, last year.

Up to now, the security community has focused mostly on the physical impacts of sea level rise on military installations, critical infrastructure and coastal habitability, said Rod Schoonover, a former U.S. intelligence officer with expertise in climate and security issues.

“But often missing in this kind of assessment,” he said, “is a recognition that the socioeconomic and behavioral impacts of sea-level rise will hit far sooner than its physical effects. How will people and institutions respond to the specter of increased rates of insurance, rent, and mortgages, and of decreased freshwater? The effects on civil society may be profound.”

Today’s U.N. Security Council discussions are critical to finding solutions, Guterres said. 

“We must keep working to protect affected populations and secure their essential human rights,” he said. “The security council has a critical role to play in building the political will required to address the devastating security challenges arising from rising seas. We must all work to continue turning up the volume on this critical issue, and supporting the lives, livelihoods and communities of people living on the front lines of this crisis.”

This article has been updated after an earlier version misstated recent research on the rate of sea level rise. The rate is 1.7 inches per decade, not 1.7 inches per year.