Indicator Assessment
Arctic and Baltic sea ice
Arctic sea ice is declining rapidly. Since 1979, the Arctic has lost, on average, an area of 79 000 km2 of sea ice per year in summer and 33 000 km2 per year in winter. The Arctic summer sea ice area in 2020 was the second lowest ever. Arctic sea ice is also getting younger and thinner. A nearly ice-free Arctic sea in summer is projected to be a rare event for 1.5 °C of global warming but the norm for 2.5 °C of warming. The maximum sea ice extent in the Baltic Sea has shown a decreasing trend since about 1800 and reached its lowest value ever in winter 2019/20. This decreasing trend is projected to continue.
Observed and projected decline in Arctic sea-ice area
Note: This figure combines two data sources. The left part of the figure (black lines) shows the observed change in Arctic sea ice are over the period 1979 to 2020 for March (maximum ice cover) and September (minimum ice cover) based on the EUMETSAT OSI SAF Sea Ice Index v2.1 dataset. The right part shows projections of the Arctic sea ice area in March and September from CMIP6 simulations for three emissions scenarios. The thick lines denote the multimodel ensemble mean (24-27 models, depending on the scenario), and the shading shows the likely uncertainty interval (one standard deviation around the multimodel mean). The dashed black line indicates a threshold for near ice-free conditions.
Over the period 1979-2020, the sea ice area in the Arctic decreased by 33 000 km2 per year in winter (measured in March) and by 79 000 km2 per year in summer (measured in September) (Figure 1, black line). The decrease in summer sea ice is more than 13 % per decade. Summer sea ice cover in each of the last 14 years (2007-2020) was lower than in any previous year since satellite measurements began in 1979. The Arctic sea ice cover in September 2019 was the second lowest ever recorded. Arctic sea ice is also getting much thinner and younger, as less sea ice survives the summer to grow into thicker, multi-year floes. The percentage of ice that is at least 5 years old declined from 30 % to about 1 % between 1979 and 2019 (Meredith et al., 2019; Schweiger et al., 2019; Blunden and Arndt, 2020).
The decline in Arctic sea ice is unprecedented in the last 1 000 years, based on historical reconstructions and paleoclimate evidence. At least half of the observed loss in summer sea ice area can be attributed to anthropogenic greenhouse gas emissions (Walsh et al., 2017; Meredith et al., 2019). The rapid changes in Arctic sea ice can trigger complex feedback processes in the global climate system, which can also affect climate and weather extremes in Europe (e.g. Vihma, 2014; Coumou et al., 2018).
All climate models agree that Arctic sea ice will continue to shrink and thin (Figure 1, coloured lines). Projections from the most recent global modelling exercise (CMIP6) suggest that a nearly ice-free Arctic sea will likely be experienced at least once before 2060, even for low emissions scenarios. An ice-free Arctic in late summer is expected to be a rare event for 1.5 °C of global warming (relative to pre-industrial levels), a frequent event for 2 °C warming, and a permanent feature for warming above 2.5 °C (Jahn, 2018; Sigmond et al., 2018; Meredith et al., 2019; SIMIP Community, 2020). Note that these details are not visible from Figure 1, because the multi-model mean shown there reduces the interannual variability compared to individual model runs. Extended simulations suggest that the Arctic could become ice-free year-round before the end of the 22nd century for the highest emissions scenario (Representative Concentration Pathway; RCP8.5) (Hezel et al., 2014).
An animation from NASA shows the decline in Arctic sea ice from 1984 to 2019
Maximum extent of ice cover in the Baltic Sea in winter and 15 year moving average
Note: The figure shows the maximum extent of ice cover in the Baltic Sea in the winters over the period 1719/20-2019/20 (blue bars) and the 15 year moving average (red line). Source: Jouni Vainio, Finnish Meteorological Institute (updated from Seinä and Palosuo 1996; Seinä et al. 2001).
The maximum winter sea ice extent in the Baltic Sea has mostly displayed a decreasing trend since about 1800. It reached a record low level in winter 2019/2020 (Figure 2). The decrease in sea ice extent appears to have accelerated since the 1980s (Haapala et al., 2015). The frequency of mild ice winters (defined as having a maximum ice cover of less than 130 000 km2) has increased from seven in 30 years in the period 1950-1979 to 16 years in the period 1991-2020, whereas the frequency of severe ice winters (at least 270 000 km2 of ice) has decreased from six years to one during the same periods.
Baltic sea ice extent and thickness are projected to continue to shrink significantly. The best estimate of the decrease in maximum ice extent over the 21st century is 640 km2/year for a medium emissions scenario (RCP4.5) and 1 090 km2/year for a high emissions scenario (RCP8.5). For the latter scenario, largely ice-free winters are projected by the end of the century (Luomaranta et al., 2014).
Indicator definition
This indicator shows trends in the area of Arctic sea ice in March (annual ice maximum) and September (annual ice minimum). Satellite observations cover the period from 1979 until now. Projections until 2100 are based on an ensemble of climate models from the CMIP6 exercise, which informs the Intergovernmental Panel on Climate Change Sixth Assessment Report. Note that earlier versions of this indicator have shown the extent rather than the area of Artic sea ice, which is closely related, but can lead to somewhat different numbers.
The indicator also shows observations of maximum annual ice extent in the Baltic sea, reaching back to 1719.
Units
- Area (km²)
Policy context and targets
Context description
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Targets
No targets have been specified.
Related policy documents
No related policy documents have been specified
Methodology
Methodology for indicator calculation
Observations of Arctic sea ice were available from the EUMETSAT OSI SAF reanalysis project, in which a consistent time series of daily, gridded data for sea ice concentration is made from the passive microwave sensors SMMR and SSM/I data. Monthly aggregated sea ice products are provided by the EUMETSAT OSI SAF. Projections for Arctic sea ice area were derived from the CMIP6 ensemble experiment.
The annual maximum ice extent in the Baltic Sea was estimated based on three sources. Ice extent for the winters of 1720-1940 is based on a construction from various sources, including observations at lighthouses, old newspapers, records of travel on ice, scientific articles, and air temperature data from Stockholm and Helsinki. Data for 1945-1995 stems from the Finnish operational ice service. Data since 1995 is based on satellite observations.
The graphs show the data as delivered; linear trend lines and moving averages were added.
Methodology for gap filling
Not applicable.
Methodology references
No methodology references available.
Uncertainties
Methodology uncertainty
Not applicable
Data sets uncertainty
No uncertainty has been specified
Rationale uncertainty
No uncertainty has been specified
Data sources
-
Arctic monthly mean sea ice area
provided by Ocean and Sea Ice Satellite Application Facility (OSI SAF) -
Arctic sea ice area for the 21st century from CMIP6 simulations (Dataset URL is not available)
provided by American Geophysical Union (AGU) -
Baltic Sea - sea ice concentration and thickness charts
provided by Copernicus Marine Environment Monitoring Service -
Maximum annual extent of ice cover in the Baltic Sea
provided by Finnish Meteorological Institute (FMI)
Other info
Typology: Descriptive indicator (Type A - What is happening to the environment and to humans?)
- CLIM 010
- CSI 053
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Geographic coverage
Temporal coverage
For references, please go to https://www.eea.europa.eu/data-and-maps/indicators/arctic-sea-ice-4/assessment or scan the QR code.
PDF generated on 20 Oct 2021, 03:50 PM
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