Sea Ice Age
Is Arctic sea ice getting older or younger?
About this map
Does sea ice get older over time in the Arctic and has that behavior changed over time? This interactive map shows monthly snapshots of sea ice age in the Arctic Ocean. A different map display is available for every month of every year in the time series.
Sea ice age data are classified into categories ranging from ice that is less than a year old to ice that is more than four years old. Sea ice age is estimated based on satellite observations of sea ice motion and extent.
Each monthly map shows how much of the Arctic Ocean is covered by sea ice, and what age the ice is. The sea ice is color-coded to indicate whether it is young, thin ice (less than a year old), or older, thicker ice. The corresponding bar graph is also color-coded to show sea ice age for that month.
Color key and bar graph
When you select a month on the dropdown selector and a year on the lower-left slider, the map will show sea ice age.
- Areas with ice that is less than a year old appear in light green, and areas with ice that is four years old or older appear in dark blue.
- Ice that is older than one year old but younger than four years old appears in intermediate shades of blue-green. The darker the shade, the older and thicker the ice. Ice-free areas are white.
In the bar graph, the bars show every year in the time series for the selected month, and the bar that correlates with the map on display is highlighted in light gray.
For every month, the bar graph categorizes sea ice by age, showing the total extent for each ice age category. Sea ice extent is NSIDC's measurement of whether an area is ice-covered, and NSIDC derives sea ice extent from estimates of sea ice concentration—the amount of sea ice in a given area, usually described as a percentage. To estimate extent, NSIDC sets a concentration threshold of 15 percent. Above that threshold, the area is considered ice-covered; below that threshold, the area is considered ice-free.
The bar graph uses a slightly different color key than the map. The graph divides sea ice age into three categories: first-year ice (lightest blue), ice that is two to four years old (medium blue), and ice that is five or more years old (darkest blue). Across the time series, the bar graph can be toggled between two states by clicking the field directly to the left of the dropdown “month” selector:
- Millions of square kilometers: This shows how much of the Arctic ocean is covered by sea ice, categorized by age.
- Percent of extent: This breaks down the percentage of total sea ice extent for each month and year by age category.
The graph incorporates all sea ice in the Arctic Ocean, including the Barents and Kara Seas, but not including ocean waters in the Canadian Archipelago.
How to change the display
- To change the month displayed on the map and graph, use the dropdown “month” selector in the bar graph box (lower right).
- To toggle between states of “millions of square kilometers” and “percent of extent,” click the field directly to the left of the dropdown “month” selector.
- To change the year, move the slider in the year box (lower left).
- To animate the time series for the selected month, click the play arrow. The animation will display maps for the selected month for all years in the time series.
For sea ice, age matters
When sea ice first forms, it is typically thin, smooth, and likely to melt completely in summer conditions. Young, thin ice easily drifts with winds and currents, resulting in more openings (leads) in the ice.
If it survives the summer, ice can thicken, becoming rougher and more resilient to changes within the atmosphere and ocean. Besides thickening, multiyear ice loses some of its salt content, which allows it to stay frozen at higher temperatures.
The roughness of multiyear ice also changes the effects of melting snow. In the springtime, first-year ice and older ice are both snow-covered, and they reflect sunlight in much the same way. As snow melts, water collects (or pools) in depressions on the surface of the ice. Rough multiyear ice develops deep depressions, so these melt ponds grow and deepen over a smaller area. In comparison, first-year ice has a smoother surface, resulting in shallow and wide melt ponds. Melt ponds are a critical component of melting. These pools of water absorb more solar radiation than the ice surface and they heat up faster. So, younger, thinner ice covered with widely spread out melt ponds absorbs more energy in the summer, enhancing melt further.
What the data show
Since 1978, polar-orbiting satellites have provided a continuous record of Arctic sea ice behavior. By comparing satellite images over time and supplementing those comparisons with observations from drifting buoys, scientists can estimate how long sea ice persists in the Arctic. Decades worth of Arctic sea ice studies show that multiyear sea ice in the Arctic has steadily declined. In fact, the overwhelming majority of sea ice in the Arctic Ocean is now thin, vulnerable first-year ice.
Decades worth of Arctic sea ice studies show that multiyear sea ice in the Arctic has steadily declined. Each year, the Arctic Report Card tracks changes in sea ice, including the amount of older, thicker ice remaining.. The Arctic Report Card: Update for 2020 reports that, in March 1985, "old" sea ice (more than four years old) comprised 33 percent of the sea ice cover in the Arctic Ocean. In March 2020, similarly old ice comprised just 4.4 percent of the Arctic Ocean sea ice cover. In March 1985, old ice covered 2.70 million square kilometers. In March 2020, old ice covered just 0.34 million square kilometers.
By viewing different months and years, you can use this map to observe changes in old versus young Arctic sea ice. Try using these maps to answer questions such as:
- In which months does first-year ice comprise the greatest percentage of Arctic sea ice cover?
- In which months does ice that is four or more years old comprise the greatest percentage of Arctic sea ice cover?
- As the years pass, where does old, thick ice persist the longest?
- In which years does old, thick ice decline most noticeably?
You can compare sea ice age maps with other maps in Satellite Observations of Arctic Change, such as maps for sea ice concentration and near-surface air temperatures.
These maps are based on observations of sea ice motion and extent.
Data source(s)
Satellite instruments and drifting buoys collect data on the formation, movements, and disappearance of sea ice. Years of accumulated observations have been used to estimate ice age since the early 1980s. The satellite data and drifting buoy information is used to derive gridded fields of sea ice drift on a 12.5 by 12.5 kilometer Equal-Area Scalable Earth Grid (EASE-Grid).
Ice age is estimated from the gridded sea ice drift fields by tracking the motion of parcels (pixels) of ice over time using the derived drift fields. A grid cell must contain at least 15 percent ice concentration to be mapped. When a grid cell survives the melt season, the grid cell ages one year. Since the sea ice minimum for the Arctic happens toward the end of summer (early to mid-September), the week following the record low marks the birthday of any ice left over. Weekly data has been averaged to create monthly values for both the maps and bar graphs.
Some regions of purely seasonal ice have not been mapped. Thus the cited values for ice coverage are less than the actual amount of ice present in the Arctic.
Explore the source data for this map:
Tschudi, M., W. N. Meier, J. S. Stewart, C. Fowler, and J. Maslanik. 2019. EASE-Grid Sea Ice Age, Version 4. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. https://doi.org/10.5067/UTAV7490FEPB. [Accessed April 10, 2021].
Data processing steps
To create this map, NSIDC took the following steps:
- Re-projection to epsg:3413 (See this guide to NSIDC's polar stereographic projection for more information.)
- Mask any nodata values
- Average weekly input data into monthly outputs
- Convert to actual year value (e.g. 5 = first year ice)
- Convert to GeoTIFF
Quick links
Why is Arctic sea ice getting younger?