Frequently Asked Questions

SeaLevelMap.io provides an interactive display of global sea level and ice sheet changes spanning the past 500,000 years. It covers the late Pleistocene and the Holocene, encompassing Marine Isotope Stages 1-13 (MIS 1-13). The steps beyond 400,000 years, where the sea level model stops, are schematic: they borrow the coastlines and ice of earlier times with the same global sea level.

The coastlines come from a model of past relative sea level computed by Dr. Jacky Austermann from the ICE-6G_C ice history (Peltier et al. 2015), applied to GEBCO's global map of the sea floor and the bedrock beneath today's ice. From 50,000 to 80,000 years ago the coastlines come instead from the sea level model of Gowan et al. (2021), which was computed from the same ICESHEET 2.0 ice the map draws and fits the dated sea level evidence better at those times. The map works on a grid of about 3.7 km, so it shows the shape of past coastlines, not local detail. Ice sheets up to 80,000 years ago come from the ICESHEET 2.0 reconstruction (Gowan et al. 2021); before that the ice is schematic (see below).

Modeling past sea level involves real uncertainties: the ice histories, the response of the solid Earth, and the present-day topography all carry error, and different models can disagree by tens of meters near the former ice sheets. Treat the map as a well-founded picture, not a survey. Learn More

Use the panel at the bottom of the screen. Drag its slider to choose a time, or press play to run forward through time to the present; the arrow keys move one step at a time. The panel shows the date and global sea level then, and under the slider a curve of global sea level over the whole span, with the selected time marked. The slider and the curve are drawn to scale in time, so the steps since the last ice age sit close together at the left end: hover over that end, or use the Last ice age button, to spread them out (see "Why are the most recent steps so close together?" below). The panel's buttons change the view: Evidence shows dated records of where the sea stood (and, on the older glacial steps, how far the ice reached), Labels hides or shows today's place names, 3D raises the land relief, and Key shows the colour scales. The compass in the top corner returns to the starting view.

Because the slider and the curve under it are drawn to scale in time. The last ice age ended fast: after the Last Glacial Maximum, about 20,000 years ago, global sea level rose by about 120 meters, most of it within about ten thousand years. Over 500,000 years that rise is a near-vertical wall at the left end of the curve. The rest of the curve shows the same pattern repeating roughly every 100,000 years: the ice builds slowly over tens of thousands of years, then melts quickly (see the graph on the Data page).

The map has nine steps from the present back to 24,000 years ago, too close together to pick out on a slider drawn to scale. Hover over the left end of the slider, or over the Last ice age button beside Present, and that stretch opens out, with the older steps squeezed to make room; a yellow bracket under the curve marks it. Move along the slider past it and it closes again. On a phone, tap the Last ice age button to open or close it.

SeaLevelMap.io does not provide predictions of future sea level changes. Projecting future sea levels involves complex models that incorporate various factors, including ice melt rates, ocean warming, atmospheric conditions, and human-induced climate change.

Given the intricate nature of these variables, accurately predicting long-term sea level changes is a scientific challenge. Our platform is primarily designed to help users explore past changes in sea level and understand the geological history of Earth's coastlines and ice sheets.

For up-to-date information on future sea level rise predictions and ongoing scientific research, we recommend visiting these reputable sources:

• NASA's Sea Level Change Portal

• NOAA's CoastWatch Program

• Climate Central's Coastal Risk Screening Tool

• UCAR's Climate Data Guide on Sea Surface Height

SeaLevelMap.io visualizes sea level changes over the past 500,000 years. For exploring sea levels and geological changes in "deeper time", beyond this period, we recommend the following resources:

• Ancient Earth by Dinosaur Pictures: This tool allows you to view the Earth's continents at various points in time, going back over 750 million years.

• Deep Time Maps: Here you can find paleogeographic maps representing the Earth's ancient landscapes through hundreds of millions of years of geologic time.

• EarthByte: The PaleoMap PaleoAtlas for GPlates provides digital maps that illustrate the plate tectonic development of ocean basins and continents, as well as the changing distribution of land and sea over the past 1100 million years.

The Last Glacial Maximum (LGM) refers to the period in Earth's history when ice sheets were at their greatest extent, around 26,000-19,000 years ago. This period is covered by the interactive map. Learn More

Marine Isotope Stages (MIS) are alternating warm and cold periods in the Earth's past, deduced from oxygen isotope data representing global ice volume and temperature change. SeaLevelMap.io covers MIS 1-13. Learn More

“BP” means Before Present, so 60k BP is 60,000 years before present.

Global mean sea level (GMSL) is the average height of the ocean's surface (the midpoint between high and low tide), used as a standard to measure land elevation and ocean depths across the globe. It's important for understanding the overall rise or fall of sea levels over time. Learn More

Glacial Isostatic Adjustment (GIA) is the ongoing movement of land once burdened by ice-age glaciers. During the last ice age, the weight of massive ice sheets caused the Earth's crust to bend and depress. When the ice melted, the land began to slowly rise, a process that continues today. This is known as GIA and it's crucial to consider when studying sea level change because it affects our understanding of the rate at which ocean basins are changing volume, and therefore, how fast water levels are rising or falling. Learn More

The map's sea level includes GIA, so it is not one global number. Near the ice sheets the land was pressed down, letting the sea reach places that are dry today: 13,000 years ago it floods the St. Lawrence valley (the Champlain Sea) and the edges of the Baltic. Around the ice, the crust bulged up, so some shores stood higher than the global average alone would suggest.

Yes! We encourage the use of SeaLevelMap.io for educational purposes. The interactive map serves as a valuable tool for visualizing Earth's geological history and understanding the science of sea levels. Please contact us if you are an educator with additional questions.

The sea level model behind the map's coastlines goes back 400,000 years. For the steps from 414,000 to 500,000 years ago, the map borrows the coastlines and ice of an earlier time in the model's record when global sea level was about the same as then, at the same point in the ice age cycle: the sea falling into a glacial, or rising out of one. The global sea level comes from the curve under the slider (Spratt & Lisiecki 2016). So these steps show what the world looked like at that sea level, not a reconstruction of that time, and the sidebar names the time each one borrows. Times when the sea stood higher than today, like the warmest part of MIS 11, can't be shown this way, because the model's record has no such time to borrow.

Up to 80,000 years ago the ice comes from ICESHEET 2.0, a reconstruction built from geological evidence of where the ice margins stood. Earlier than that, no such reconstruction exists, so the map uses the ICE-6G ice history the sea level model was run with. It repeats ICE-6G's ice shapes from one glacial cycle to the next and comes on a coarser grid, so its outlines are smoother and should be read as schematic.

At every step the ice is shaded by thickness, from its plain colour at thin margins to pale blue where it is over 1, 2 and 3 km thick. The thickness comes from ICE-6G; up to 80,000 years ago it is trimmed to ICESHEET's outlines, so the outlines stay ICESHEET's own.

Not on the scale of North America's or northern Europe's. At the Last Glacial Maximum the mountains of Asia held extensive glaciers, along the Himalaya and the Kunlun, across the Tien Shan and the Altai, and as ice caps on the Tibetan Plateau, but the plateau itself was not buried under a continental ice sheet. At the 24,000 and 20,000-year steps the map shows these mountain glaciers, and those of the Andes, the Alps, New Zealand and other ranges, from GLACIMONTIS (Lima et al. 2025), a global compilation of glacier reconstructions. Each range reached its greatest extent at its own time, so they show the glaciers' greatest extent around the Last Glacial Maximum.

Before 80,000 years the ice the map draws is schematic: it repeats ICE-6G's ice shapes from one glacial cycle to the next. On the steps within the older glacial stages (MIS 5b, MIS 6, MIS 8 and MIS 10, and the warm MIS 5c) the Evidence button adds a dashed red line showing how far the ice actually reached according to the geological evidence, from Batchelor et al. (2019). It marks the ice's greatest extent at any time during the stage, not the ice at that moment. During MIS 6, around 132,000 to 190,000 years ago, it shows a Eurasian ice sheet reaching much further south and east than the schematic ice, across the northern European plain and into Russia. The evidence for MIS 8 and 10 is thin and debated, so those lines are highly uncertain.

It raises the land relief and tilts the map, so mountain ranges and plateaus stand out. Heights are exaggerated 25 times; at the scale of a globe, real mountains would be too small to see. Drag with the right mouse button, or with two fingers on a phone, to tilt and turn the view. The sea and the ice stay flat: the raised relief is today's bedrock above sea level, the same at every time step, so land exposed by lower seas and the domes of the ice sheets are not raised.

As the ice sheets melted back, meltwater pooled against their edges in huge proglacial lakes. Lake Agassiz, the largest, at its peak covered more area than all of today's Great Lakes combined, and the Great Lakes basins held larger, differently shaped lakes such as glacial Lake Chicago and Lake Algonquin. The map shows these lakes at seven steps from 20,000 to 5,000 years ago, from the Geological Survey of Canada's maps of the ice's retreat (Dyke et al. 2003). Those maps are dated in radiocarbon years, so each step uses the one closest to the ice it shows, converted to calendar years; the sidebar says which. While the proglacial lakes are shown, today's lakes are hidden. The layer covers North America only.

Before 20,000 years ago there are no such maps, so at six steps from 100,000 to 24,000 years ago the lakes come from a model instead (Austermann et al. 2022): it works out where meltwater would pool against the ice on land pressed down by its weight. The model was run with its own ice history, so the map shows only its larger lakes that lie beside the ice drawn here, and they are less certain than the mapped ones, so they are drawn in a paler blue. Today's lakes stay visible at these steps.

It shows dated evidence of past sea level: shells, peat, corals, raised beaches and other samples whose age and height show where the sea stood. They come from GAPSLIP, Evan Gowan's global archive of sea level indicators. Each record appears at the time step nearest its age, within 500 years for recent steps and up to 3,000 years for older ones, and its colour says what it shows: yellow where sea level stood at that height, blue where it stood above it (the sample formed under the sea), brown where it stood below it (the sample formed on land). Click a dot for its site, age, height and source. On the older glacial steps it also draws a dashed red line where the ice reached (see "What is the dashed red line on the older ice?" above).

The records measure relative sea level, like the map's coastlines, so they can be set against them: where a blue dot sits on land, the evidence says the sea was there. Most records are from the last 15,000 years and from coasts in Europe, North America, Greenland, Asia and Australia, so earlier steps have only a few. Around the Baltic between about 16,900 and 9,500 years ago the records give the Baltic's water level, as the basin was a lake for much of that time.

The map has grown from 135,000 to 500,000 years, and our goal is to keep expanding and evolving it. Please contact us if you would like to contribute. Any updates will be communicated on our social channels.