What Happens If Sea Levels Rise Like They Did in the Eemian?

The Eemian Interglacial: A Time of Warmth and High Seas

Roughly 129,000 to 116,000 years ago, the Eemian Interglacial was a period when the earth was just a bit warmer than it is today. Global average temperatures were about 1 to 2 degrees Celsius higher than pre-industrial times. As a result, vast portions of the polar ice sheets melted, pouring meltwater into the world’s oceans. Sea levels soared to heights between 6 and 9 meters above what we see now. The world map looked different: coastlines were drawn further inland, and islands disappeared beneath the waves. The Eemian shows us just how sensitive our planet’s ice sheets—and our coastlines—are to even small changes in temperature.

How Much Water Is 6 to 9 Meters of Sea Level Rise?

Six to nine meters of sea level rise might sound abstract, but it packs a punch. That’s enough to completely submerge many low-lying cities and reshape entire countries’ borders. For context, the Statue of Liberty’s pedestal is about 8 meters high—imagine water lapping at her toes. In sheer volume, this means trillions of tons of ice turned to water, flooding coastlines around the globe. Major deltas like the Nile and the Mekong would be underwater. Even places hundreds of kilometers from the sea could find their rivers swelling dangerously higher than ever before.

Why Did the Eemian Seas Rise So High?

The primary driver of high sea levels during the Eemian was melting ice—especially from Greenland and West Antarctica. Warmer temperatures caused these massive ice sheets to retreat, and the water they held spilled into the oceans. Scientists believe that much of the rise came from Greenland, which may have lost up to a third of its ice. The West Antarctic Ice Sheet, vulnerable to melting from below, likely contributed as well. Some researchers even suggest that parts of the East Antarctic Ice Sheet collapsed, adding more water. The lesson? Even a modest global temperature increase can unleash dramatic changes.

Modern Sea Level Rise: How Fast Are We Catching Up?

Today, sea levels are rising faster than at any point in the last few millennia. Since 1900, global sea level has climbed about 20 centimeters (8 inches), with the rate accelerating in recent decades. In the last 30 years, the pace has roughly doubled. Melting glaciers, shrinking ice sheets, and the thermal expansion of seawater all contribute. If greenhouse gas emissions continue unchecked, scientists warn we could see several meters of rise by 2100—or sooner—putting us on a path eerily similar to the Eemian.

The Fate of Coastal Cities

If seas rise 6 to 9 meters, iconic cities like New York, London, Shanghai, and Miami would be at risk of partial or total inundation. In New York, the famous subway system would be flooded, and neighborhoods like Lower Manhattan would become underwater relics. London’s Thames Barrier would be overwhelmed, while Shanghai’s financial district would vanish beneath the tide. Miami, already battling king tides, would be mostly lost to the ocean. Millions would have to abandon their homes, sparking a wave of climate refugees and humanitarian crises.

Disappearing Islands and Sinking Nations

Entire island nations could vanish if sea levels rise as they did in the Eemian. The Maldives, Tuvalu, and Kiribati are only a few meters above sea level at their highest points. Such a rise would leave them submerged, erasing cultures, languages, and histories in a matter of decades. Even larger islands like the Bahamas and parts of Indonesia would lose vast swathes of land. The loss goes beyond geography—it’s a loss of identity and heritage for millions.

Flooded River Deltas and Agricultural Heartlands

River deltas are among the most fertile places on Earth, providing food for hundreds of millions. The Nile, Ganges-Brahmaputra, Mekong, and Mississippi deltas would be devastated by a 6 to 9 meter rise. Rich agricultural land would be swallowed by saltwater, displacing farmers and destroying crops. The humanitarian impact would be massive, with food shortages rippling out to affect global supply chains. Imagine trying to grow rice in a field that’s become part of the sea.

Redrawing the World Map: New Coastlines

If Eemian-level sea rise occurred, the world map would look shockingly different. Coastlines would retreat by miles, and new bays and inlets would form where cities and fields once stood. In the United States, Florida would shrink to a fraction of its current size. The Netherlands, famous for its low-lying polders, would struggle to exist. Even large inland lakes and rivers would expand, flooding valleys and altering ecosystems. Cartographers would be forced to redraw borders, and nations would scramble to define their new realities.

Impact on Freshwater Resources

As saltwater pushes further inland, freshwater sources become contaminated. Coastal aquifers, which millions rely on for drinking water, would turn brackish or salty. Cities like Dhaka and Manila, already facing water shortages, would be hit especially hard. Farmland irrigated with this tainted water would yield less, worsening food crises. In some places, entire freshwater lakes could become saline, altering habitats for fish and birds.

Wildlife on the Move: Ecosystem Upheaval

Sea level rise doesn’t just affect people—it upends ecosystems. Coastal marshes, mangroves, and wetlands would drown or be pushed inland, if space allows. Species that depend on these habitats, from shorebirds to turtles, would be forced to migrate or die out. In some cases, new habitats might form, but not quickly enough to save threatened species. Coral reefs, already stressed by warming waters, could be lost to deeper, murkier seas, ending vibrant marine communities.

Economic Catastrophe: The Price of Inaction

The financial toll of Eemian-like sea level rise would be almost unimaginable. Trillions of dollars in coastal property, infrastructure, and economic activity would be at risk. Insurance markets would collapse in flood-prone regions, and governments would face huge bills for adaptation or relocation. Tourism, fisheries, and ports would all be disrupted. The global economy could spiral, all because of unchecked climate change and melting ice sheets.

Mass Migration and the Human Toll

As the sea swallows homes and farmland, people will be forced to move. Experts predict hundreds of millions of climate refugees in a world with Eemian-level sea rise. Urban centers would swell as displaced people arrive with nowhere else to go. Social tensions could rise, competition for jobs and housing could become intense, and some countries might even close their borders. The human cost of inaction becomes heartbreakingly clear.

Losing Cultural Heritage and History

Some of humanity’s most treasured historical sites lie near the sea. Venice, the Pyramids of Egypt, ancient temples in Southeast Asia—all risk flooding or erosion from rising seas. Museums, archives, and archaeological sites would be lost forever, erasing connections to our shared past. In some cases, artifacts could be salvaged, but for many, the sea would become their final resting place.

Storm Surges: Higher Seas, Deadlier Storms

Storm surges are already a threat, but with higher baseline sea levels, their impact magnifies. Hurricanes and typhoons would push water further inland, flooding neighborhoods never before at risk. Emergency services would be stretched to the limit. Recovery after storms would take longer and cost more, with each new disaster compounding the last. For coastal residents, every storm would bring fresh dread.

Changing Ocean Currents and Weather Patterns

When ice melts and seas rise, ocean currents can shift. These currents drive global weather, affecting rainfall, droughts, and even heatwaves. If the North Atlantic Current weakens, Europe could see colder winters, even as the planet warms. Changes in ocean circulation could trigger unpredictable climate swings, making weather more extreme and less reliable. Farmers, fishermen, and everyday people would have to adapt to a world that plays by new rules.

Loss of Biodiversity in Coastal Zones

Rich coastal habitats like estuaries and tidal flats support an incredible variety of life. As these habitats drown or are squeezed out by urban development, countless species could vanish. Fisheries would suffer, birds would lose nesting grounds, and local economies would feel the pinch. Once diverse, bustling ecosystems could become barren, with ripple effects reaching far inland and across the globe.

Health Risks from Waterborne Diseases

Flooded cities and farmlands can become breeding grounds for disease. Pathogens thrive in warm, stagnant floodwaters, leading to outbreaks of cholera, malaria, and other illnesses. Drinking water supplies contaminated by salt or sewage would worsen the crisis. Hospitals, already under pressure, would struggle to keep up. Vulnerable populations—children, the elderly, the poor—would suffer the most.

Adapting Infrastructure: Can We Build Our Way Out?

Coastal defenses like seawalls and levees might buy time, but they’re expensive and not always effective. Many cities would need to move vital infrastructure—power plants, airports, sewer systems—farther inland. Some regions might experiment with floating buildings or artificial islands, but these solutions are costly and can’t help everyone. The challenge is immense: can we rebuild fast enough, or is retreat the only option?

The Psychological Impact: Anxiety, Loss, and Resilience

Living with rising seas brings more than physical challenges—it takes a toll on mental health. Watching your home, your history, and your future slip underwater is an emotional gut punch. Anxiety and depression rise in flood-prone communities, and the trauma can linger for generations. Yet, people also show remarkable resilience. Communities band together, find creative solutions, and fight to protect what they love. The human spirit is tested, but not easily broken.

Learning from the Past: The Eemian’s Cautionary Tale

The Eemian stands as a stark warning: Earth’s ice sheets can melt faster and more dramatically than we might expect. By studying ancient shorelines, pollen, and fossils, scientists piece together a picture of a world transformed by warmth. The lesson couldn’t be clearer—if temperatures rise, the seas will follow. The choices we make today will echo for centuries, shaping the world for generations yet unborn.

The Race Against Time: Will We Act?

With every year that passes, the window to prevent Eemian-like sea level rise narrows. Cutting emissions, investing in renewable energy, and protecting vulnerable coastlines are urgent tasks. Scientists warn that delaying action could lock in catastrophic changes, making adaptation harder and more expensive. The clock is ticking, and the stakes couldn’t be higher. Will we rise to the challenge, or will we watch our world change beyond recognition?