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Indicator Assessment
Past trends
In the period 1979–2015, the sea ice extent in the Arctic decreased by 42 000 km2 per year in winter (measured in March) and by 89 000 km2 per year in summer (measured in September) (Figure 1), which, based on historical records, is likely unprecedented since the 14th century [i]. The maximum sea ice extent in March 2015 and March 2016 were the lowest on record. Arctic sea ice loss is driven by a combination of warmer ocean waters and a warmer atmosphere, including an earlier onset of summer surface melt [ii]. In contrast, Antarctic sea ice has reached record high levels in recent years, but the expansion of the Antarctic sea ice has been less than half of the loss of Arctic sea ice [iii].
Changes in Arctic sea ice may trigger complex feedback processes. Warming and a longer melt season result in increased solar heat uptake by the ocean, which delays the autumn refreeze [iv]. However, a warmer atmosphere means that there are more clouds and, in summer, these reflect sunlight, thus representing a negative feedback mechanism. Even so, some evidence suggests that winter regrowth of ice is inhibited by the warmer ocean surface [v]. Thinner winter ice leads to more heat loss from the ocean and a warmer atmosphere, and hence thicker cloud cover, which inhibits the escape of heat to space [vi], which is a positive feedback mechanism.
The minimum Arctic sea ice cover at the end of the melt season in September 2012 broke all previously observed records. All years since 2002 have been below the average for 1981–2010 (Figure 1). Comparison of recent sea ice coverage with older ship and aircraft observations suggests that summer sea ice coverage may have halved since the 1950s [vii]. Since more reliable satellite observations started in 1979, summer ice has shrunk by 10 % per decade [viii]. Between 1979 and 2011, the reduction of sea ice has significantly reduced albedo, corresponding to an additional 6.4 ± 0.9 W/m2 of solar energy input into the Arctic Ocean region since 1979. Averaged over the globe, this albedo decrease corresponds to a forcing that is 25 % of that due to the change in CO2 during this period [ix].
The Arctic sea ice is also getting thinner and younger, as less sea ice survives the summer to grow into thicker multi-year floes [x]. A recent analysis has found that annual mean ice thickness has decreased from 3.59 m in 1975 to 1.25 m in 2012, i.e. a 65 % reduction in less than 40 years [xi]. This supports findings from calculations of sea ice volume from satellites and an earlier estimate by the Pan Arctic Ice-Ocean Modeling and Assimilation System (PIOMAS) ([1]), which suggests that the mean monthly sea ice volume has decreased by about 3 000 km3/decade since 1979 [xii].
Information on sea ice extent in the Baltic Sea goes back to 1720. The maximum sea ice extent has displayed a decreasing trend most of the time since about 1800 (Figure 2). The decrease in sea ice extent appears to have accelerated since the 1980s, but large interannual variability makes it difficult to demonstrate this statistically [xiii]. The frequency of mild ice winters, defined as having a maximum ice cover of less than 130 000 km2, has, however, increased from seven in 30 years in the period 1950–1979 to 15 in the period 1986–2015. The frequency of severe ice winters, defined as having a maximum ice cover of at least 270 000 km2, has decreased from six to four during the same periods.
Projections
Improving the ability to track the observed rapid summer-time melting of Arctic sea ice has been a challenge for modelling [xiv], but observations fall well within the model range in recent modelling studies [xv]. All model projections agree that Arctic sea ice will continue to shrink and thin. For high greenhouse gas emissions scenarios, a nearly ice-free Arctic Ocean in September is likely to occur before mid-century (Figure 3) [xvi]. An extension beyond 2100 suggests that, for the highest emissions scenario (RCP8.5), the Arctic could become ice-free year-round before the end of the 22nd century; on the other hand, a recovery of Arctic sea ice could become apparent in the 22nd century if stringent policies to reduce global greenhouse gas emissions, and eventually concentrations, are successfully implemented [xvii].
Projections of Baltic Sea ice extent under different emissions scenarios suggest that the maximal ice cover and ice thickness will continue to shrink significantly over the 21st century. The best estimate of the decrease in maximum ice extent from a model ensemble is 6 400 km2/decade for a medium emissions scenario (RCP4.5) and 10 900 km2/decade for a high emissions scenario (RCP8.5); for the latter scenario, largely ice-free conditions are projected by the end of the century [xviii].
Further information
An animation from NOAA shows the decline in multi-year Arctic sea ice extent from 1987 to 2014: https://youtu.be/FDRnH48LvhQ
[i] J. Halfar et al., ‘Arctic Sea-Ice Decline Archived by Multicentury Annual-Resolution Record from Crustose Coralline Algal Proxy’,Proceedings of the National Academy of Sciences 110, no. 49 (3 December 2013): 19737–41, doi:10.1073/pnas.1313775110.
[ii] M. Collins et al., ‘Long-Term Climate Change: Projections, Commitments and Irreversibility’, inClimate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, ed. T. F. Stocker et al. (Cambridge; New York: Cambridge University Press, 2013), 1029–1136, http://www.climatechange2013.org/images/report/WG1AR5_Chapter12_FINAL.pdf.
[iii] Claire L. Parkinson, ‘Global Sea Ice Coverage from Satellite Data: Annual Cycle and 35-Yr Trends’,Journal of Climate 27, no. 24 (December 2014): 9377–82, doi:10.1175/JCLI-D-14-00605.1.
[iv] Sharon Stammerjohn et al., ‘Regions of Rapid Sea Ice Change: An Inter-Hemispheric Seasonal Comparison’,Geophysical Research Letters 39 (16 March 2012): L06501, doi:10.1029/2012GL050874.
[v] Jennifer M. Jackson, William J. Williams, and Eddy C. Carmack, ‘Winter Sea-Ice Melt in the Canada Basin, Arctic Ocean’,Geophysical Research Letters 39 (15 February 2012): L03603, doi:10.1029/2011GL050219.
[vi] Stephen P. Palm et al., ‘Influence of Arctic Sea Ice Extent on Polar Cloud Fraction and Vertical Structure and Implications for Regional Climate’,Journal of Geophysical Research 115 (12 November 2010): D21209, doi:10.1029/2010JD013900.
[vii] Walter N. Meier, Julienne Stroeve, and Florence Fetterer, ‘Whither Arctic Sea Ice? A Clear Signal of Decline Regionally, Seasonally and Extending beyond the Satellite Record’,Annals of Glaciology 46, no. 1 (October 2007): 428–34, doi:10.3189/172756407782871170.
[viii] Josefino C. Comiso et al., ‘Accelerated Decline in the Arctic Sea Ice Cover’,Geophysical Research Letters 35 (3 January 2008): L01703, doi:10.1029/2007GL031972; M.A. Killie and T. Lavergne, ‘Time Series of the 1979 to 2010 Monthly Arctic Sea-Ice Extent in March (the Month of Sea-Ice Extent Maximum) and September (the Month of Sea-Ice Extent Minimum) in km2’ (Data produced by the EUMETSAT OSI SAF (http://osisaf.met.no) and the CryoClim (http://www.cryoclim.net) project, delivered through MyOcean, 2011).
[ix] Kristina Pistone, Ian Eisenman, and V. Ramanathan, ‘Observational Determination of Albedo Decrease Caused by Vanishing Arctic Sea Ice’,Proceedings of the National Academy of Sciences 111, no. 9 (3 April 2014): 3322–26, doi:10.1073/pnas.1318201111.
[x] Josefino C. Comiso, ‘Large Decadal Decline of the Arctic Multiyear Ice Cover’,Journal of Climate 25, no. 4 (February 2012): 1176–93, doi:10.1175/JCLI-D-11-00113.1.
[xi] R. Lindsay and A. Schweiger, ‘Arctic Sea Ice Thickness Loss Determined Using Subsurface, Aircraft, and Satellite Observations’,The Cryosphere 9, no. 1 (helmikuu 2015): 269–83, doi:10.5194/tc-9-269-2015.
[xii] Axel Schweiger et al., ‘Uncertainty in Modeled Arctic Sea Ice Volume’,Journal of Geophysical Research 116 (27 September 2011): C00D06, doi:10.1029/2011JC007084, updated with PIOMAS data available online.
[xiii] Jari J. Haapala et al., ‘Recent Change — Sea Ice’, inSecond Assessment of Climate Change for the Baltic Sea Basin, ed. The BACC II Author Team (Cham: Springer International Publishing, 2015), 145–53, http://link.springer.com/10.1007/978-3-319-16006-1_8.
[xiv] Julienne C. Stroeve et al., ‘Trends in Arctic Sea Ice Extent from CMIP5, CMIP3 and Observations’,Geophysical Research Letters 39, no. 16 (2012): L16502, doi:10.1029/2012GL052676.
[xv] P. J. Hezel, T. Fichefet, and F. Massonnet, ‘Modeled Arctic Sea Ice Evolution through 2300 in CMIP5 Extended RCPs’,The Cryosphere 8, no. 4 (heinäkuu 2014): 1195–1204, doi:10.5194/tc-8-1195-2014.
[xvi] F. Massonnet et al., ‘Constraining Projections of Summer Arctic Sea Ice’,The Cryosphere 6, no. 6 (22 November 2012): 1383–94, doi:10.5194/tc-6-1383-2012; Stroeve et al., ‘Trends in Arctic Sea Ice Extent from CMIP5, CMIP3 and Observations’; Muyin Wang and James E. Overland, ‘A Sea Ice Free Summer Arctic within 30 Years: An Update from CMIP5 Models: Summer Arctic Sea Ice’,Geophysical Research Letters 39, no. 18 (September 2012): L18501, doi:10.1029/2012GL052868; Collins et al., ‘Long-Term Climate Change: Projections, Commitments and Irreversibility’; James E. Overland and Muyin Wang, ‘When Will the Summer Arctic Be Nearly Sea Ice Free?’,Geophysical Research Letters 40, no. 10 (2013): 2097–2101, doi:10.1002/grl.50316.
[xvii] Hezel, Fichefet, and Massonnet, ‘Modeled Arctic Sea Ice Evolution through 2300 in CMIP5 Extended RCPs’.
[xviii] Anna Luomaranta et al., ‘Multimodel Estimates of the Changes in the Baltic Sea Ice Cover during the Present Century’,Tellus A 66, no. 22617 (4 April 2014), doi:10.3402/tellusa.v66.22617.
In April 2013, the European Commission (EC) presented the EU Adaptation Strategy Package. This package consists of the EU Strategy on adaptation to climate change (COM/2013/216 final) and a number of supporting documents. The overall aim of the EU Adaptation Strategy is to contribute to a more climate-resilient Europe.
One of the objectives of the EU Adaptation Strategy is Better informed decision-making, which will be achieved by bridging the knowledge gap and further developing the European climate adaptation platform (Climate-ADAPT) as the ‘one-stop shop’ for adaptation information in Europe. Climate-ADAPT has been developed jointly by the EC and the EEA to share knowledge on (1) observed and projected climate change and its impacts on environmental and social systems and on human health, (2) relevant research, (3) EU, transnational, national and subnational adaptation strategies and plans, and (4) adaptation case studies.
Further objectives include Promoting adaptation in key vulnerablesectors through climate-proofing EU sector policies and Promoting action by Member States. Most EU Member States have already adopted national adaptation strategies and many have also prepared action plans on climate change adaptation. The EC also supports adaptation in cities through the Covenant of Mayors for Climate and Energy initiative.
In September 2016, the EC presented an indicative roadmap for the evaluation of the EU Adaptation Strategy by 2018.
In November 2013, the European Parliament and the European Council adopted the 7th EU Environment Action Programme (7th EAP) to 2020, ‘Living well, within the limits of our planet’. The 7th EAP is intended to help guide EU action on environment and climate change up to and beyond 2020. It highlights that ‘Action to mitigate and adapt to climate change will increase the resilience of the Union’s economy and society, while stimulating innovation and protecting the Union’s natural resources.’ Consequently, several priority objectives of the 7th EAP refer to climate change adaptation.
No targets have been specified.
Input data was 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 generated by CryoClim.
The annual maximum ice extent in the Baltic Sea was estimated utilizing the material of the Finnish operational ice service from the winters of 1945-1995 and information collected by Prof. Jurva from the winters of 1720-1940. The latter originated from various sources, including observations at lighthouses, old newspapers, records on travel on ice,scientific articles, and air temperature data from Stockholm and Helsinki.
Projections for Northern Hemisphere sea ice extent were derived from the CMIP5 ensemble experiment.
The graphs show the data as delivered; trend lines were added.
Not applicable
Not applicable
Data on the cryosphere vary significantly with regard to availability and quality. Snow and ice cover have been monitored globally since satellite measurements started in the 1970s. Improved technology allows for more detailed observations and observations of a higher resolution.
Continuous efforts are being made to improve knowledge of the cryosphere. Scenarios for the future development of key components of the cryosphere have recently become available from the CMIP5 project, which has provided climate change projections for the IPCC AR5. Owing to their economic importance, considerable efforts have also been devoted to improving real-time monitoring of snow cover and sea ice.
No uncertainty has been specified
For references, please go to https://www.eea.europa.eu/data-and-maps/indicators/arctic-sea-ice-2/assessment or scan the QR code.
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