Will the Arctic be free of summer ice in 30 years?

פורסם: 8 בנוב׳ 2013, 4:04 על ידי: Sustainability Org   [ עודכן 8 בנוב׳ 2013, 4:38 ]
Satellite observations show the Arctic has been losing sea ice for the past 30 years   Computer models predict that by 2035, the Arctic could be nearly sea ice free in summer
Figure 1. Sea ice minima in September of 1980, 2007 and 2008. Sea ice images from NASA/Goddard Space Flight Center Scientific Visualization Studio.Thanks to Rob Gerston (GSFC) for providing the data. Composite graphic from NOAA.   Figure 2. Model projections of sea ice thickness when the Arctic is nearly ice free in September, within 30 years. Units for sea ice thickness are meters. Figure from Wang and Overland1

Arctic sea ice loss is occuring 30 years earlier than was anticipated...

Recent Arctic sea ice coverage is the lowest in the satellite record (since 1979) and is occurring at least 30 years earlier than was anticipated in the recent assessment report issued by the Intergovernmental Panel on Climate Change.

Arctic sea ice extent observed by satellites has been shrinking for the past 30 years. The minimum sea ice extent is seen at the end of summer in 2007, 2008, and 2009 are the three lowest during the satellite era. Although the extent of the 2009 summer sea ice cover was more than that in 2007 and 2008, it is still 25% below the average for 1979-2000.

These sea ice minima open more than 40% of the Arctic Ocean to increased absorption of warmth from the sun near the end of summer. Extensive open water has been observed in the Chukchi Sea, the East Siberian Sea and north of the Barents Sea.

As the summer melt season lengthens and intensifies, there is less sea ice at summer's end. Major delays have occurred in the timing of fall freezeup since 2005.

Over 40% of the thick sea ice that was built up over many winters (nearly 10 feet thick), has melted and is replaced with thinner ice formed in a single year.

Once this process has started, it is difficult to reverse.

What will happen to Arctic sea ice in the next 30 years?

Using the observed 2007/2008 summer sea ice extents as a starting point (Figure 1, above), computer models predict that the Arctic could be nearly sea ice free in summertime within 30 years (Figure 2, above).1

Computer simulations indicate that Arctic sea ice retreat will not continue at a constant rate into the future. Instead they show several abrupt decreases in summer Arctic sea ice cover in the futue. The projections for a likely ice retreat suggests that the Arctic could transition from perennial year-round ice to seasonal winter ice, with numerous implications for the climate system.2

Sea ice thickness, concentration and age is reduced in the warmer Arctic

In Figure 3 (below, left) the blue color indicates areas where the Arctic sea ice concentration3 was reduced by as much as 50% of the amount normally observed in October.

Anomalies (above) represent October 2010 deviations from normal October sea ice concentration.
Sea ice age derived from drift tracking of ice floes for the first week of March in a) 1988, b) 2008, c), 2009, and d) 2010. The panels illustrate the substantial loss in the oldest ice types within the Arctic Basin in recent years compared to the late 1980s.
Figure 3. Anomalies (above) represent October 2010 deviations from normal October sea ice concentration. Figure from National Snow and Ice Data Center.
   Figure 4. Sea ice age derived from drift tracking of ice floes for the first week of March in a) 1988, b) 2008, c), 2009, and d) 2010. (Figure courtesy of National Snow and Ice Data Center, J. Maslanik and C. Fowler).

Figure 4 (above, right) shows how old, thick Arctic sea ice, built up over many years, is being replaced by thinner, younger ice in recent years. The four panels show the age of the sea ice in March for different years. Sea ice age is used as a rough indicator of sea ice thickness.

In 1988, large areas of the Arctic Ocean were covered by multi-year sea ice that is five or more years old (red colors in Figure 4(a)). In 2008, 2009 and 2010, these areas of older sea ice had dwindled to a small strip near the coast from Alaska to Greenland (red colors in Figure 4 (b), (c), and (d)), indicating that in these years, old 5-year sea ice was replaced by younger, thinner and less resilient ice.

The thick component of the perennial ice, called multi-year ice, as detected by satellite data during the winters of 1979–2011 was studied5, and results reveal that the multi-year ice extent and area are declining at a rapid rate of 215.1% per decade and 217.2% per decade, respectively, with a record low value in 2008 followed by higher values in 2009, 2010, and 20115.

  End of Winter End of Summer
Now Modeled sea ice thickness in the top row is for the year when the modeled ice coverage matched current values in Spring (left) and Autumn (right). The bottom row shows model projections of sea ice thickness when the Arctic is nearly ice free in summertime, within 30 years (Spring on left, Autumn on right). Figure from Wang and Overland.
In 30
Years
Figure 5. Modeled sea ice thickness in the top row is for the year when the modeled ice coverage matched current values in Spring (left) and Autumn (right). The bottom row shows model projections of sea ice thickness when the Arctic is nearly ice free in summertime, within 30 years (Spring on left, Autumn on right). Figure from Wang and Overland1

The pale areas in Figure 5 (to the right) denote thicker sea ice (3-6 feet or 1-2 meters thick), and dark blue areas denote thinner sea ice (less than 3 feet or 1 meter thick), as computed by models.

The top row of Figure 5 shows conditions for the year when the computer simulated September sea ice extent reachs current values. By the end of winter, much of the central Arctic is covered by sea ice less than 8 feet or 2.5 meters thick (top left). At the end of summer (in September), much of the remaining sea ice in the central Arctic is less than 4 feet or 1.2 meters thick (top right).

The bottom row of Figure 5 shows conditions for the year when the models predict a nearly sea ice-free Arctic, about 30 years later. At the end of winter, much of the modeled sea ice is less than 6.5 feet or 2.0 meters thick (bottom left). At the end of summer, the sea ice that remains is very thin (bottom right).

In the year when the models predict a nearly sea ice-free Arctic, about 30 years from now, only a small area north of the Canadian Archipelago and Greenland (the small white area in the image at the bottom right) retains some sea ice approaching a thickness of 6.6 feet or 2 meters.

 

arrow See the latest Arctic Report Card update on Sea Ice

arrow Learn more about Computer models and uncertainty in predictions of sea ice loss

References and definitions

1 Wang, M., and J.E. Overland (2009): A sea ice free summer Arctic within 30 years? Geophys. Res. Lett., 36, L07502, doi: 10.1029/2009GL037820.

2 Holland, M.M., C.M. Bitz, and B. Tremblay (2006): Future abrupt reductions in the summer Arctic sea ice. Geophys. Res. Lett., 33, L23503, doi:10.1029/2006GL028024.

3 Sea ice concentration is the amount of sea ice in a given area.

4 Inoue, J., and M. Hori (2011) Arctic cyclogenesis at the marginal ice zone: A contributory mechanism for the temperature amplification? Geophys. Res. Lett., doi:10.1029/2011GL047696, in press. [PDF] (accepted 17 May 2011)

5 Comiso, Josefino C., 2012: Large Decadal Decline of the Arctic Multiyear Ice Cover. J. Climate, 25, 1176–1193. doi: http://dx.doi.org/10.1175/JCLI-D-11-00113.1 [PDF version]


Source: noaa.gov

How the loss of sea ice leads to a warmer Arctic

With reduced summer sea ice, additional solar heat is absorbed in the upper ocean, from the surface to a depth of about 65 feet (20 meters). This heat is released slowly from the ocean to the atmosphere during the following Autumn, increasing atmospheric temperatures up to about 1 mile above the surface (Figure 1).

How much warmer is the Arctic?

The red colors in Figures 2 and 3 (below) indicate areas over the Arctic where autumn near-surface air temperatures in recent years were up to 10.8 °F (6°C) warmer than those typically observed in the years prior to 2002.

From 2002 to 2005, as the extent of Arctic summer sea ice began to decline, autumn air temperatures near the surface began to rise above normal (Figure 2). As the loss of sea ice accelerated, and low or record-setting low sea ice extents were observed at the end of summer from 2007-2010 (Figure 3), autumn Arctic air temperatures near the surface rose further above normal values, and elevated temperatures were seen over larger areas of the Arctic.

Anomalies for autumn in 2002-2005 represent deviations from the normal near surface air temperature values which were observed from 1968-1996) Anomalies for autumn 2007-2010 represent deviations from the normal near surface air temperature values which were observed from 1968-1996)


Figure 2. Anomalies for autumn in 2002-2005 represent deviations from the normal near surface air temperature values which were observed from 1968-1996. Figure from Overland and Wang1.   Figure 3. Anomalies for autumn 2007-2010 represent deviations from the normal near surface air temperature values which were observed from 1968-1996. Figure from NOAA/ESRL Physical Sciences Division.

Rises in near surface air temperatures throughout the 21st century are projected to be especially pronounced over the Arctic Ocean during the cold season, largely driven by loss of sea ice cover.2

Heat released from the warmer Arctic changes the Arctic atmosphere

As sea ice cover is diminished during autumn, air temperature near the surface is increased, decreasing the stable stratification of the lower atmosphere.1 The result is a dome of warm air and elevated pressure surfaces over much of the Arctic ocean.

Elevated pressure surfaces over the Arctic are are indicated by red and yellow colors in Figure 4 (below) for autumn 2002-2010.

Note that some of the largest pressure surface elevations, shown in red, occur from the East Siberian Sea to northern Alaska, a region of diminished summer sea ice cover for every year from 2002-2010.

Figure 4. Anomalies represent deviations from normal pressure surface elevations over the Arctic. Anomalies represent deviations from normal east-west winds over the Arctic.


Figure 4. Deviations from normal autumn pressure surface elevations over the Arctic seen from 2002-2010. Figure from NOAA/ESRL Physical Sciences Division. graphic from NOAA.   Figure 5. Anomalies for autumn 2002-2010 represent deviations from normal east-west winds over the Arctic. Figure from NOAA/ESRL Physical Sciences Division.

The warmer Arctic and changes in the Arctic atmosphere may impact the Polar Vortex

The elevated pressure surfaces above the North Pole persist into early winter, setting up conditions that tend to weaken the strong Polar Vortex winds that normally circle the Arctic in a counterclockwise direction, and may impact large scale wind patterns over the Northern Hemisphere, potentially allowing cold air to move southward.

Figure 5 (above) shows the changes in the Northern Hemisphere wind fields that are associated with late autumn surface air temperature and earlier sea loss. Blue and purple colors indicate areas with wind deviations below normal. Note the much reduced winds north of Alaska and western Canada.1

As summer Arctic open water area increases over the next decades, we anticipate there is the potential for an increasing influence of loss of summer sea ice on the atmospheric northern hemisphere general circulation in following seasons which may have impacts on northern hemisphere weather.5

cartoon showing Heat absorbed in ice-free areas of the Arctic ocean in summer is released to the atmosphere in autumn

 

Figure 6. NOAA/AVHRR infrared satellite image of explosive frontal cylone generation observed by the Japanese RV Mirai in the Beaufort Sea on September 24, 2010. The ship's location is indicated in red. Figure from Inoue and Hori (2011).4

Sea ice retreat contributes to Arctic cyclone generation

The Arctic is warming faster than the rest of the globe, due to the decrease in Arctic sea ice. With less sea ice cover, the ocean absorbes more heat from the sun during summer, increasing the temperature contrast between the warm ice-free ocean and cold ice surfaces in autumn. The large temperature contrast contributes to the generation of Arctic cyclones. In the late September 2010, Japanese Research Vessel Mirai observed the explosive generation of an Arctic cyclone, shown in Figure 6.4

Scientists analyzing observations from the Mirai concluded that this is an invaluable example of the fact that sea ice retreat contributees to polar amplification of surface air temperature increase and that cyclone generation is important in the transfer of the excess heat from the ocean into the atmosphere.4

References

1 Overland, J.E., and M. Wang (2010): Large-scale atmospheric circulation changes associated with the recent loss of Arctic sea ice. Tellus, 62A, 1–9.

2 Serreze, M.C., A.P. Barrett, J.C. Stroeve, D.N. Kindig, and M.M. Holland (2009): The emergence of surface-based Arctic amplification. The Cryosphere, 3, 11–19.

3 Stroeve, J. C., J. Maslanik, M. C. Serreze, I. Rigor, W. Meier, and C. Fowler, 2011. Sea ice response to an extreme negative phase of the Arctic Oscillation during winter 2009/2010, Geophys. Res. Lett., 38, L02502, doi:10.1029/2010GL045662.

4 Inoue, J., and M. Hori (2011) Arctic cyclogenesis at the marginal ice zone: A contributory mechanism for the temperature amplification? Geophys. Res. Lett., doi:10.1029/2011GL047696. [PDF]

5 Francis, J. A. and S. J. Vavrus (2012), Evidence linking Arctic amplification to extreme weather in mid-latitudes, Geophys. Res. Lett., 39, L06801, doi:10.1029/2012GL051000.

6 Duarte CM, Lenton TM, Wadhams P, Wassmann P. (2012), Abrupt climate change in the Arctic. Nat Clim Chang. 2011;2:60–62.

Source: noaa.gov

Warm Arctic - Cold Continents

The Polar Vortex

Cold air is normally trapped in the Arctic in winter by strong Polar Vortex winds, which circle the North Pole from west to east and the strong pressure field that is shown in purple/blue colors in Figure 1a, below left. This pattern broke down in December 2009, and in February 2010, (Figures 1b and 1c, below middle and right). North-south winds increased, allowing cold Arctic air to spill southwards.

Normal 850 mb geopotential height values which were observed for December from 1968-1996   850 mb geopotential height values which were observed for December 2009   850 mb geopotential height values which were observed for February 2010
(a) Average December value for 1968-1996
(b) December 2009

(c) February 2010
Figure 1. Arctic Atmospheric Pressure: normal 850 mb geopotential height values which were observed for December from 1968-1996 (left) and unusual 850 geopotential height values that were observed for December 2009 (middle) and for February 2010 (right). Figures from NOAA/ESRL Physical Sciences Division.

Warm Arctic - Cold Continents

This creates the Warm Arctic-Cold Continent Pattern, shown in Figure 2 below for December 2009 and 2010. Red colors indicate areas where the Arctic was 9°F or 5°C warmer than normal. Purple colors indicate areas where the continents were 9°F or 5°C cooler than normal. Warmer than normal Arctic temperatures were seen especially in regions that were sea-ice-free in summer: north of Alaska and in the Barents Sea. The cold continents are seen where Arctic air penetrated southward. Some warm air penetrates northward near Bering Strait and east Greenland.

Anomalies for December 2009 represent deviations from the normal 1000 mb air temperature values which were observed from 1968-1996.   Anomalies for December 2010 represent deviations from the normal 1000 mb air temperature values which were observed from 1968-1996.
(a) December 2009   (b) December 2010
Figure 2. Warm Arctic (red) - Cold Continents (purple) pattern in (a) December 2009 and (b) December 2010. Shown are anomalies or deviations from the normal 1000 mb air temperature values which were observed from 1968-1996. Data are from the NCEP-NCAR Reanalysis through the NOAA/ESRL Physical Sciences Division.

The Polar Vortex was weak in other years as well. In late autumn and early winter 2005, 2008, 2010, but especially 2009, a weak Polar Vortex and associated increase in southward flowing winds coming out of the Arctic brought record cold and snow conditions to northern Europe, eastern Asia and eastern North America. In autumn 2009, Northern Eurasia (north of 50° latitude to the Arctic coast) and North America (south of 55° latitude) were particularly cold, 3 -18° F cooler than the normal monthly average, and Arctic regions were more than 7°F warmer than average.

The North Atlantic Oscillation (NAO) climate index had it's lowest value in 145 years for Winter 2009/2010

One indicator of a weak Polar Vortex is the North Atlantic Oscillation (NAO) index. Winter 2009/2010, which saw two major winter cold continent events, had the lowest NAO value in 145 years of historical record. In other years, Winter 2005-2006 had a primary influence in Eurasia and December 2008 had a more local influence in northeastern Canada.

Influences on sub-Arctic weather

Meteorological attribution to these sub-Arctic events is difficult. The last five years have been the warmest recorded period in the Arctic and climate conditions over the Arctic cannot be ruled out as influencing weather in some sub-Arctic regions, making it relative colder for part of the winter.

Certainly many factors, including random chaos in the development of weather patterns, can produce such extreme winter events. For example, the US experienced severe winter weather in early February 2011, but the NAO and Arctic pressure fields were not necessarily strong. This serves to show that not all severe weather events can be directly attributed to changes in the Arctic.

Sub-Arctic weather can also be influenced by changes in the Arctic stratosphere, snow cover, and other climate forcing such as El Nino. More combined observational and modeling studies to understand causes and latitudinal extent of this recent Warm Arctic – Cold Continent pattern are a high priority in Arctic research. In summary, the most we can now say is that loss of sea ice pushes in the right direction to weaken the Polar Vortex and increase the chance for sub-Arctic impacts.

References

1Honda, M., J. Inoue, and S. Yamane (2009): Influence of low Arctic sea-ice minima on anomalously cold Eurasian winters. Geophys. Res. Lett., 36, L08707, doi:10.1029/2008GL037079.

2Strey, S.T., W. Chapman, and J. Walsh (2009): Effects Of An Extreme Arctic Sea Ice Minimum On the Northern Hemisphere Atmosphere During Late Autumn and Early Winter:, Eos Trans. Eos Trans. AGU, 90(52), Fall Meet. Suppl., Abstract C41A-0421.

3Francis, J.A., W. Chan, D.J. Leathers, J.R. Miller, and D.E. Veron (2009), Winter Northern Hemisphere weather patterns remember summer Arctic sea-ice extent, Geophys. Res. Lett., 36, L07503, doi:10.1029/2009GL037274.

4 Budikova, D. (2009): Role of Arctic sea ice in global atmospheric circulation: A review. Global Planet. Change, 68(3), 149–163.

5 Petoukhov, V., and V. Semenov (2010): A link between reduced Barents-Kara sea ice and cold winter extremes over northern continents. J. Geophys. Res.-Atmos., ISSN 0148-0227.

6Serreze, M. C., A. P. Barrett, and J. J. Cassano (2011), Circulation and surface controls on the lower tropospheric air temperature field of the Arctic, J. Geophys. Res., 116, D07104, doi:10.1029/2010JD015127.

7 Overland, J.E., K.R. Wood, and M. Wang (2011): Warm Arctic–cold continents: Impacts of the newly open Arctic Sea. Polar Res., 30, 15787, doi: 10.3402/polar.v30i0.15787. [PDF Version]

8 Jiping Liu, Judith A. Curry, Huijun Wang, Mirong Song, and Radley M. Horton (2012). Impact of declining Arctic sea ice on winter snowfall PNAS 2012 ; published ahead of print February 27, 2012, doi:10.1073/pnas.1114910109

9 Francis, J. A. and S. J. Vavrus (2012), Evidence linking Arctic amplification to extreme weather in mid-latitudes, Geophys. Res. Lett., 39, L06801, doi:10.1029/2012GL051000.

10Duarte CM, Lenton TM, Wadhams P, Wassmann P. (2012), Abrupt climate change in the Arctic. Nat Clim Chang. 2011;2:60–62.

Source: noaa.gov

Why changes in the Arctic matter globally: Glaciers and Sea Level1

Normal 850 mb geopotential height values which were observed for December from 1968-1996  

Surface meltwater disappears down a moulin. Near the ice margin in the Ilulissat region, West Greenland

© Konrad Steffen/CIRES, University of Colorado
  850 mb geopotential height values which were observed for December 2009  
Drained glacier dammed meltwater lake reveals walls of bue ice. Near Helheim Glacier, Southeast Greenland

© Henrik Egede Lassen
/Alpha Film
  850 mb geopotential height values which were observed for February 2010  

Soil particles on the ice sheet surface near the margins further accelerate the melting process

© Henrik Egede Lassen
/Alpha Film
 
Acknowledgement: AMAP is the source of these materials.
Anyone wishing to use these materials for commercial purposes should contact amap@amap.no.

Arctic glaciers, ice caps and the Greenland Ice Sheet contributed over 40% of the global sea level rise of around .118 inches (3 mm) per year observed between 2003 and 2008. In the future, global sea level is projected to rise by 3 to 5.2 feet (0.9-1.6 m) by 2100 and Arctic ice loss will make a substantial contribution to this.2

Changes in the Arctic cryosphere3 have impacts on global climate and sea level1

All the main sources of freshwater entering the Arctic Ocean are increasing — river discharge, rain/snow, and melting glaciers, ice caps, and the Greenland Ice Sheet. Recent calculations estimate that an extra 1847 cubic miles (7700 km3) of freshwater — equivalent to one metre of water over the entire land surface of Australia — has been added to the Arctic Ocean in recent years. There is a risk that this could alter large-scale ocean currents that affect climate on a continental scale.

Melting glaciers and ice sheets worldwide have become the biggest contributor to global sea level rise. Arctic glaciers, ice caps, and the Greenland Ice Sheet contributed .118 inches (3 mm) — over 40% — of the total .122 inches (3.1 mm) global sea level rise observed every year between 2003 and 2008. These contributions from the Arctic to global sea level rise are much greater than previously measured.

High uncertainty surrounds estimates of future global sea level. Latest models predict a rise of 3 to 5.2 feet (0.9 to 1.6 m) above the 1990 level by 2100, with Arctic ice making a significant contribution.

Major Greenland ice sheet loss in 2010 is thought to be related to regional Arctic sea ice loss and increased warm winds from the south.

References and Definitions:

12011 Snow, Water, Ice and Permafrost in the Arctic (SWIPA) assessment - coordinated by AMAP and produced in collaboration with IASC, WMO/Clic and IASSA - Executive Summary (30MB download)

2Key finding 13 in the 2011 Snow, Water, Ice and Permafrost in the Arctic (SWIPA) assessment.

3The cryosphere is the part of the Earth's surface that is frozen for some part of the year. It includes frozen water in the form of sea ice, glacier ice, ice sheets, ice caps, snow cover, lake and river ice, and frozen ground.

Source: noaa.gov

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