Download 5.3.2 Glaciers

5.3 Cryosphere
5.3.1 Introduction
The cryosphere is the frozen part of the world. It includes all permanent or seasonal snow and
ice deposits on land, in the seas, in rivers and lakes and in the ground (permafrost). It is the
second largest component of the climate system after the oceans with regard to mass and heat
capacity. Snow and ice play a key role in the earth’s energy budget by reflecting heat from the
sun due to its light surfaces. As melting replaces white surfaces with darker, more heat is
being absorbed (the albedo effect). Three quarters of the world’s freshwater resources are
frozen. Snow and ice play a key role in the water cycle and are essential for storing fresh
water for the hotter and often dryer seasons.
The cryosphere is important for the exchange of gases between the ground and the
atmosphere – among these several greenhouse gases, e.g. methane. Finally, ice and snow are
defining components of ecosystems in the northern parts of the Northern hemisphere and in
high mountain areas. Many plants and animals have evolved to live under these conditions
and can not live without. The cryosphere hence plays a major role in various dimensions of
the climate system: it is affected if the climate changes, but its own changes affect the climate
system in turn. Therefore, monitoring these changes provides crucial knowledge about climate
change.
Selection of indicators
The various components play strong but different roles within the climate system:
 Due to their large volumes and areas, the two continental ice sheets of Greenland and
Antarctica actively influence the global climate over very long time scales. Sea level
can however be affected more rapidly.
 Snow covers a large area too, but has relatively small volume. It is important for key
global interactions and feedbacks like increased uptake of heat (albedo effect).
 Sea ice also covers a large area. It is important due to its albedo and its impacts on
ocean circulation, which transports heat from equator to the poles.
 Melting permafrost release the strong greenhouse gas methane from frozen organic
material. Together with seasonal snow, it influences the water content in the soil and
the vegetation.
 Glaciers, ice caps and seasonal lake ice, with their smaller areas and volumes, react
relatively quickly to changes in climate, influencing ecosystems and human activities
on a local scale. They are good indicators of climate change.
The selected indicators cover strategic information from all these compartments of the
cryosphere: glaciers and snow cover in Europe, the Greenland ice sheet, the Arctic sea ice and
mountain permafrost in Central Europe. Lake and river ice conditions are presented in the
water chapter.
Indicators and vulnerability
The cryosphere is vulnerable to global warming. It is a very visible expression of climate
change. It integrates climate variations over a wide range of time scales, from millennia to
seasonal variations throughout the year. This can complicate interpretations of why changes
happen.
In Europe, the most vulnerable areas are the high mountain areas, and the Arctic. Both in the
Arctic and the European Alps, temperatures have increased more than global rate in the past
few decades; in the Arctic as a whole, twice as much. The amount of ice and snow, especially
in the Northern Hemisphere has decreased substantially over the last few decades due to
increased temperatures. European glaciers shrink, snow covered areas creep higher up and
further north, sea ice in the Arctic melts and gets thinner, permafrost starts to thaw, and the
Greenland ice sheet shows increasing signals of disintegration and thawing at its borders.
These trends will accelerate as climate change is projected to continue. However, there are
also large uncertainties to the fate of key components of the cryosphere; it is not possible to
give reliable predictions of when the Arctic sea ice may melt completely in summer. Neither
is it possible now to predict the future of the Greenland ice sheet with any confidence
Data and info sources
Data on the components of the cryosphere are quite different with regard to availability and
quality. Long-term data records on glaciers of all European glaciated areas are provided in a
considerable good quality and quantity by the World Glacier Monitoring Service (WGMS) in
Zürich. Data on snow cover and Arctic sea ice have been measured globally since satellite
measurements started in the 1970s and are available e.g. at the Global Snow and Ice Data
Centre (NSIDC) in Boulder/U.S.A. However sensors in the satellites are gradually improved,
allowing for new observations. Hence area-wide data on the Greenland ice-sheet are often
available for not longer than 15 years. This is also the situation for data on mountain
permafrost measured in boreholes which are drilled into frozen rock walls.
The gaps in the cryospheric data base are well recognized by the scientific community and
many efforts are taken to improve the knowledge, e.g. during the International Polar Year
(IPY) 2007 - 2009.
5.3.2 Glaciers
Key Messages
• The vast majority of glaciers in the European glacial regions are in retreat.
•
•
•
Since 1850, glaciers in the European Alps have lost approximately two thirds of their volume, with
clear acceleration since 1985.
Glacier retreat is projected to continue. A 3°C warming of average summer air temperature could
reduce the currently existing glacier cover of the European Alps by some 80 %. With ongoing
climate change nearly all of the smaller glaciers and one third of the overall glacier area in
Norway are projected to disappear by 2100.
Glacier retreat has serious consequences for river flow. It impacts freshwater supply, river
navigation, irrigation and power generation. It could cause natural hazards and damages to
infrastructure.
Presentation of the main indicator
Figure 5.3.2.1.: Cumulative ice loss (in mm) of glaciers from all European regions with glaciers
Source: World Glacier Monitoring Service (www.wgms.ch), 2006.
Relevance
Glacier changes are among the most visible indications of the effects of climate change. Glaciers are
particularly sensitive to changes in the global climate because their surface temperature is close to the
freezing/melting point (Zemp et al., 2007). Glacier fluctuations show a strong relation to air
temperature throughout the 20th century (Greene, 2005), and a strong physical basis exists to explain
why warming would cause mass loss (IPCC, 2007a). Therefore their mass balance, resulting from
accumulation (mainly snow fall) and ablation (mainly melting and calving), is considered as a
immediate signal for the early detection of global warming trends. Glaciers are important freshwater
resources and act as `water towers’ for the lower lying regions. With a diminished ice mass, the annual
melt water and therefore the contribution to river flow and sea level rise is decreasing in the long term.
This will cause serious consequences for freshwater supply, river-navigation, irrigation facilities, and
power generation. Further the solute release from melting rock-glaciers may impact the water quality
of high-mountain lakes adversely by intrusion of heavy metals (Thies et al., 2007).
Strong retreat of glaciers can cause glacier instabilities with hazardous incidents such as glacier lake
outbursts, rock-ice avalanches and landslides (Pralong et al., 2005; Huggel et al., 2007). This may
cause more damage to infrastructure. Glacier retreat affects tourism and winter sports in the mountains
(OECD, 2007) and changes the appearance of mountain landscapes.
Adaptation options, such as improved glacier monitoring, water management measures, draining of
glacier-lakes and construction of protective walls can reduce some of the risks and negative
consequences, but not all.
Past trends
According to the high-quality data-records of the WGMS in all of the European glacier regions, a
general loss of glacier mass has been observed (Fig.: 5.3.2.1). Glacier retreat in Europe started after
the maximum glacier-extent of the so-called ‘Little Ice Age’ in the middle of the nineteenth century. In
the Alps, glaciers lost one third of their surface and one half of their volume between 1850 and 1970s.
After 1985 an acceleration in glacial retreat has been observed, which led to a loss of 25% of the
remaining ice until 2000 (Zemp et al., 2006). This culminated in a further ice loss of 5-10% in the
extraordinary hot and dry summer of 2003 (Zemp et al., 2005), and resulted in a total loss of about 2/3
of ice mass until present. This is illustrated by the shrinking of the Vernagtferner-glacier in Austria
(Fig.: 5.3.2.2).
Also the Norwegian coastal glaciers, which were expanding and gaining mass due to increased
snowfall in winter up to the end of the 1990s, are retreating now by reduced winter precipitation and
greater summer melting (Nesje et al., 2007; Andreassen et al, 2005).
Glaciers in Svalbard are experiencing mass loss at lower elevations, and the fronts of nearly all
glaciers there are retreating (Haeberli et al., 2005, 2007; Nuth et al. 2007). Some ice caps in northeastern Svalbard seem to increase in thickness at higher elevations (Bamber et al., 2004, Bevan et al.,
2007). However, estimates for Svalbard as a whole show the total balance is negative (Hagen et al.
2003), and there is a clear signal of accelerated melting at least in western Svalbard (Kohler et al.,
2007).
Very recent findings by the WGMS (UNEP, 2008) indicate a clearly increased annual reduction of the
global-mean ice-thickness of glaciers since the turn of millennium (0.5m) compared to the 1980-1999
period (0.3 m). Some of the most dramatic shrinking has taken place in Europe (Scandinavia, Alps,
and Pyrenees).
The centennial retreat of European glaciers is mainly attributed to increased summer temperatures.
However, changes in winter precipitation, the decreased glacier albedo due to lack of summer snow
fall and various other feedback processes alter the pattern on regional and decadal scale. The recent
strong warming has made disintegration and down wasting increasingly dominant causes of glacier
decline in the European Alps during the most recent past (Paul et al., 2004).
Projections
According to a recently published sensitivity study (Zemp, 2006) the European Alps could lose about
80 % of their currently existing glacier cover, should summer air temperatures rise by 3° C and a
precipitation increase of 25 % for each 1°C would be needed to offset the glacial loss. The modelled
remains of Alpine glaciers as a consequence of warming is presented in Fig. 5.3.2.3. Sugiyama et al.
(2007) investigated the potential evolution of Rhone Glacier, Switzerland, in the 21st century based on
a model considering more the glacier flow dynamics. They found increasing mass loss as well, but to a
gradual lesser extent. However, both modelling studies did not consider feedback processes such as
the development of glacier lakes, which might accelerate the glacier retreat dramatically.
Recent climate scenarios for Norway basing on model calculations of the British Headley Centre and
the German Max Planck Institute which follow the SRES B2 emission-scenario indicate a rise in
summer-temperature by 2.3°C and an increase in winter-precipitation by 16% in the period 2070-2100
compared to the period 1961-1990. As a result, nearly all of the smaller Norwegian glaciers are likely
to disappear and the overall glacier area as well as the glacier volume may be reduced by about one
third at 2100 (Nesje et al., 2007).
Fig.5.3.2.3: Modeled remains of the glacier cover in the European Alps (climatic accumulation area)
for an increase in average summer air temperature of +1 to +5 °C.
(The total of 100% refers to the ice cover of the period 1971–1990).
Source: Zemp, M., 2006
Figure 5.3.2.2: Shrinking of the Vernagt-ferner glacier, Austria
Source: Commission of Glaciology, Bavarian Academy of Sciences; Munich, 2006
www.glaziologie.de
5.3.3. Snow cover
Key Messages
• The northern hemisphere's snow cover extent has decreased at a rate of 1.3% per decade during the
•
•
last 40 years. The greatest losses are in spring and summer.
Model simulations project widespread reductions of extent and duration of snow cover in Europe
over the 21st century.
Changes in snow cover affect the Earth surface reflectivity, river discharge, vegetation, agriculture
and animal husbandry, tourism, snow sports, transport and power generation.
Presentation of the main indicator:
Fig. 5.3.3.1: Differences in the distribution of
March-April average snow-cover in Europe
between earlier (1967-1987) and later
((1988-2004) portions of the satellite era (%
coverage).
Negative values (brown) indicate greater
extent of snow cover in the earlier portion.
Red curves show the 0°C and 5 °C isotherms
averaged for March and April 1967 to 2004
Source:
modified from Lemke et al. (2007)
Fig. 5.3.3.2: Northern Hemisphere
snow-cover extent departures from
monthly means from 1966 to 2005
Source: Brodzik, 2006 (NOAA-data)
Relevance
Snow covers more than 33 % of the land surface north of the equator from November to April. It
reaches a maximum of approximately 45.2 million km2 in January, and a minimum of about 1.9
million km2 in August (Clark et al., 1999a).
Snow cover is an important feedback mechanism in the climate system. The extent of snow cover
depends on the climate e.g. on temperature, precipitation and solar radiation. But it also influences the
climate and climate-related systems by its high reflectivity, insulating properties, its effects on water
resources and ecosystems, and cooling of the atmosphere. Thus a decrease in snow cover reduces the
reflection of solar radiation, contributing to an accelerated climate change. Changes in extent,
duration, thickness and properties of snow cover have an impact on water availability, as for domestic
use, navigation and power generation. Changes in snow cover affect human well-being through
influences on agriculture, infrastructure, and livelihoods of Arctic indigenous people, environmental
hazards and winter recreation. Snow cover retreat can reduce complications in winter road and rail
maintenance, affecting the exploitation and transport of oil and gas in cold regions (UNEP, 2007;
ACIA, 2004).
Shallow snow cover at low elevations in temperate regions is the most sensitive to temperature
fluctuations and hence most likely to decline with increasing temperature (IPCC, 2007).
For several of these impacts, adaptation can reduce the negative implications of snow cover change.
Some adaptation options, such as artificial snowmaking in the Alps to maintain tourism as a main
source of income, have to be balanced against their negative implications for mitigation, due to
increased energy use and greenhouse gas emissions.
Past trends
Data from satellite monitoring (NESDIS-database at NOAA) from 1966 to 2005 show that monthly
snow-cover extent in the Northern Hemisphere is decreasing at a rate of 1.3% per decade (Fig.
5.3.3.2), with the strongest retreat in spring (Fig. 5.3.3.1) and summer (UNEP, 2007). It has declined
in all months except November and December, with the most significant decrease during May to
August (Brodzik et al., 2006). This was accompanied by lower springtime water content, earlier
disappearance of continuous snow cover in spring (by almost two weeks in the 1972-2000 period;
Dye, 2002), less frequent frost days (days with minimum temperature below 0°C) and shorter frostseasons (period of consecutive frost days).
The trends in duration and depths of Northern Hemispheric snow cover at higher latitudes differ by
region. In contrast to a reduced duration of snow cover over North America, a long term increase in
depth and duration has been observed over most of northern Eurasia (Kitaev et al., 2005).
Snow cover trends in mountain regions of Europe vary largely with region and altitude. Recent
declines in snow cover have been documented in mountains of Switzerland (e.g. Scherrer et al., 2004)
Slovakia (Vojtek et al., 2003), and in the Spanish ski-resorts as in the Sierra Nevada and the Pyrenees
(Rodriguez et al., 2005), but no change was observed in Bulgaria over the 1931 to 2000 period
(Petkova et al.,2004). Declines, when observed, were largest at lower elevations, and Scherrer et al.
(2004) statistically attributed the declines in the Swiss Alps to warming. Lowland areas of central
Europe are characterised by recent reductions in annual snow cover duration by about 1 day/year
(Falarz, 2002). At Abisko in subarctic Sweden, increases in snow depth have been recorded since
1913 (Kohler et al., 2006), and trends towards greater maximum snow depth but shorter snow season
have been noted in Finland (Hyvärinen, 2003).
Projections
Model simulations project widespread reductions in snow cover over the 21st century (IPCC, 2007).
Decreases of between 9 and 17% in the annual mean NH snow cover by the end of 21st century are
projected by individual models (ACIA, 2004). Although winter precipitation is projected to increase in
northern and central Europe (Christensen et al., 2007), less frequent frost occurrence associated with
higher temperatures are projected to reduce the number of days with snow cover (Fig. 5.3.3.3).
Decreases of more than 60 snow cover days are projected (in the period 2071-2100 compared to the
period 1961-1990) to occur around the northern Baltic Sea, on the west slope of the Scandinavian
mountains and in the Alps (Jylhä et al., 2007). The beginning of the snow accumulation season (the
end of the snowmelt season) is projected to be later (earlier), and the snow coverage is projected to
decrease during the snow season (Hosaka et al., 2005).
For every 1 °C increase in average winter-temperature, the snowline rises by about 150 metres in the
European Alps (Beniston, 2003a). Regional climate model runs, following the SRES emission
scenarios A1B, B1 and A2, project milder winters with more precipitation in this region, increasingly
falling as rain (Jacob et al, 2007). A recently published study on sensitivity of the Alpine snow cover
to European temperature by Hantel et al. (2007) reported a distinctive variation of snow-cover
sensitivity to temperature change with altitude and estimated a reduction of about 30 days in snow
duration (snow cover of at least 5 cm) in winter at the height of maximum sensitivity (about 700m) for
a 1°C increase in temperature over central Europe (5-25°E and 42.5-52.5°N).
Snowfall in lower mountain areas is likely to become increasingly unpredictable and unreliable over
the coming decades (Elsasser and Bürki, 2002), with consequences for natural snow-reliability and
therefore difficulties in attracting tourists and winter sport enthusiasts in the future (OECD, 2007).
Fig. 5.3.3.3 Annual number of days with snow cover over land areas
(a) Observed means in northern Europe, 1961-1990 (coloured dots) and modelled means for
Europe, 1961-1990, based on seven regional climate model simulations (contours) ;
(b) Projected multi-model mean changes for the period 2071-2100, relative to 1961-1990
Source: Jylhä et al., 2007
5.3.4 Greenland ice sheet
Key Message (approx. 10 lines)
• The ice loss from the Greenland ice sheet increased in the 1990s from a near balance to
approximately 100 billion tons lost per year. It may have doubled again by 2005 (UNEP
2005). Acceleration in the outlet glaciers’ discharges to the sea accounts for more than the net
loss from melting (Rignot et al 2006).
• The corresponding contribution to global sea level rise has been suggested having increased
from 0,14 to 0,28 mm/year between 1993 and 2003. In the long run, melting ice sheets have
the largest potential to increase sea level.
* It is not possible to give reliable predictions of the future of the ice sheets yet; Processes
causing the faster movements of the glaciers are poorly understood and there is a lack of long
term observations.
Presentation of the main indicators
Figure 5.3.4.1: Calculations of the rates of mass changes in Greenland ice sheet demonstrate
increased ice loss over time, but also uncertainties in the most recent estimates since
estimates from the same period do not overlap. The rectangles depict the time period of
observations (horizontal) and the upper and lower estimates of mass balance (vertical) as
calculated by different techniques. Open bars refer to direct calculations from gravity
measuring satellites, filled bars are other techniques. (Thomas et al 2008).
Total Melt Area
April - October
Area Melted (km2)
3.00E+07
2007
1998
2.50E+07
1987
2005
2007
2002
1991
1995
2.00E+07
1.50E+07
1983
1996
1.00E+07
1992
5.00E+06
1978
1983
1988
1993
1998
2003
2008
Year
The figure includes additional maps of previous years are available at:
http://cires.colorado.edu/science/groups/steffen/greenland/melt2007/greenland%20melt%202007.pdf
Figure 5.3.4.2: The area of Greenland ice sheet where there is at least one day of surface melting in
summer has increased with a new record extent in 2007. Melting now has passed 2500 meters
elevation (Updated from Steffen et al 2004). This also led to a record ice loss according to the first
results from gravity measurements (S.Luthcke in Nature April 2008)
Relevance
The polar ice sheets in Greenland and Antarctica contain 98-99% of the freshwater ice on Earth’s
surface. The frozen water stored in Antarctica equals a 57 meters rise in global sea level, whereas the
water in the Greenland ice equals 7 meters. When setting their upper estimate of 59 cm sea level rise at
the end of this century, the IPCC did not take into account increased discharges into the oceans from
the ice sheets’ moving outlet glaciers. The uncertainty about their future is therefore a main reason for
uncertainties in projections of sea level rise. The Greenland ice sheet is the most susceptible to
warming because of its vicinity to the Atlantic Ocean and other continents. But also the more isolated
Antarctica now seems to have a net loss of ice that may be accelerating (UNEP 2007). (See indicator
on sea level)
The speed of ice loss is important in addition to the magnitude because a faster increase in sea level
reduces the time to take appropriate adaptation measures.
The melt water from Greenland will contribute to reduce the salinity of the surrounding ocean. An
upper layer of fresher water may reduce the formation of dense deep water, one of the mechanisms
setting up global ocean circulation.
Past trends
The Greenland ice sheet is a huge inland glacier with several glacier tongues calving into the
sea. It covers roughly 80% of Greenland, The average ice thickness is 1600 meters, with the highest
summit reaching 3200 meters above sea level. It has a volume of approximately 3 million km3.
Until recent improvements in remote sensing, it was hard to measure whether the polar ice sheets were
growing or shrinking. Still most time series are short. There is however a general consensus from
different approaches that the ice loss from the Greenland ice sheet has accelerated; from a near balance
in the early 90s, it reached about 100 billion tonnes lost per year at the end of the century and may
have doubled again by 2005 (UNEP 2007). The first estimates from summer 2007 show a new record
ice loss. However, there is still considerable discrepancy between different estimates of ice loss rates
(see figure 1)
The estimated contribution to sea level rise increased from 0,14 to 28 mm/year between 1993 – 2003
according to IPCC (IPCC WG 1, page TS-23).
The ice has thickened in the interior of the Greenland ice sheet above 2000 meters since it has received
more snowfall – in average about. 4 cm/year since 2000. This gain has been more than offset by the
loss in lower-lying regions.
The ice loss is partly caused by increased surface melting, the melt water runoff exceeding the snow
accumulation, leading to a negative “surface mass balance”. Air temperatures on the ice sheet have
increased by about 7 degrees Fahrenheit since 1991. For the western parts of Greenland, the
melting area increased by 30% from 1997 to 2006. A new record melt area was registered in 2007
(figure 2).
The other explanation is changes in the ice dynamics; the speed of glaciers. Large amounts of
meltwater form rivers and melting ponds at the surface and penetrate through crevasses to the bottom.
The water probably lubricates the bedrock-ice interface, making the glaciers move faster. However,
also ocean temperatures and topography of the fiords can influence the movements of the glaciers with
floating outlet tongues. Outlet glaciers act as “bathtub drains” to the inner ice; ice is being transported
into the melting zone, and calving into the ocean increases. The fastest flowing glacier, Jacobshavn
on the west coast, has sped up nearly twofold the last decade. Individual glaciers are also
reported to slow down, possibly around a new equilibrium. The phenomenon is widespread mostly on
the southeast coast and has moved northwards to ap.70o N. Acceleration is associated with large
retreats and thinning. Near the outlets, surface elevation can subside with tens of metres.
The acceleration of the outlet glaciers (ice dynamics) has been estimated to cause as much as 2/3 of
the ice loss from Greenland in 2005 (Rignot and Kanagaratnam 2006).
Projections
It is not possible to predict the future development of the Greenland ice sheet with confidence. Glacier
models account mostly for accumulation of snow during winter and melting in summer (surface mass
balance). The processes at the bottom of the glaciers believed to cause their acceleration are not
understood well and can therefore not be modelled with confidence. The sensitivity of the Greenland
ice sheet to global warming therefore largely is unknown – also if there are tipping points that can
accelerate the melting because of positive feed-backs.
Deep ice core drillings can give some indications. The Eem period 120 000 years ago was
approximately 5 degrees warmer than today, but the Greenland ice did not melt down completely. Sea
level rose 5 meters above today’s level, with the melting Greenland ice contributing 1-2 meters (Dahl
Jensen, pers. com).
The ice sheets of Greenland and Antarctica have been associated with slow climate responses over
thousands of years. But the acceleration of ice movement has caused a rethinking of how fast they
respond to warming. Paleodata show periods of rapid melting of the large continental ice sheets after
the last ice age, resulting in average rise of sea level with 1 cm/year and peak rates up to 4 cm/year
(UNEP 2007). If current trends continue, it seems likely that there will be a faster ice loss than
previously expected, leading to a higher rise in sea level than IPCC’s upper estimate of +59 cm by the
end of the century. As to the ocean circulation, the IPCC projects a 25% reduction of the North
Atlantic Current in this century, but no abrupt changes.
5.3.5 Arctic Sea Ice
Key Messages
•
The sea ice extent in the Arctic has declined at an accelerating rate, especially in
summer. The record low ice cover September 2007 was roughly half the size of the normal
minimum extent in the 1950s.
*
The summer ice is projected to continue to shrink and may even disappear at the
height of the summer melt season in the upcoming decades. There will still be substantial ice
in winter.
•
Reduced polar ice will speed up global warming and is expected to impact ocean
circulation and weather patterns. Species specialized for life in the ice are threatened.
*
Less ice will ease the access to the Arctic’s resources. Oil and gas exploration,
shipping, tourism and fisheries will offer new economic opportunities, but also increase
pressures and risks to the Arctic environment.
Presentation of the main indicator(s)
Figure 5.3.5.1: Time trends of sea-ice extent
(Will be combined in one graph with absolute values of extent at y-axis):
The figures are taken from NSIDC: http://nsidc.org/arcticseaicenews/2008/040708.html
http://nsidc.org/news/press/2007_seaiceminimum/20071001_pressrelease.html
Data can be retrieved here: http://nsidc.org/data/easytouse.html#seaice
Arctic sea ice grows to its greatest yearly amount in March and melts to its lowest yearly
amount in September. The figure shows the average ice extents for these two months after
1979. The linear trend for March indicates that the Arctic is losing an average of 44,000
square kilometers of ice per year for that month. The corresponding value for September is 72
000 square kilometres (Source: National Snow and Ice Data Centre).
Figure 5.3.5.2: The 2007 minimum sea ice extent
The extent of the summer sea ice in September 2007 reached a historical minimum, 39%
below the climatic average for the first two decades of satellite observations (red line). The
weather conditions that summer was dominated by clear sky. Continuous warm winds blew
the ice towards the coast of Canada-Greenland and out in the North East Atlantic (Source:
National Snow and Ice Data Centre).
Relevance
Reduction in Arctic sea ice has several feedbacks to the climate system. Snow- covered ice
reflects 85% of the sunlight (high albedo), whereas open water reflects only 7% (low albedo).
Less ice and snow will therefore both accelerate the sea ice decline and global warming.
Reduced ice formation will also reduce formation of dense deep water which contributes to
drive ocean circulation. As the ice cover influences air temperature and circulation of air
masses, changes in weather patterns such as storm tracks and precipitation can be expected
even at mid-latitudes (Serreze et al 2007).
The sea ice is an ecosystem filled with life uniquely adapted to these conditions, from micro
organisms in channels and pores inside the ice, rich algae communities underneath, to fish,
seals, whales and polar bears. The diversity of life in the ice grows with the age of the ice
floes. As the ice gets younger and smaller, the abundance of ice associated species will be
reduced with a risk of extinction for some of them. Arctic indigenous peoples adapted to
fishing and hunting such species will face large economic, social and cultural changes.
Less summer ice will ease the access to the Arctic Ocean’s resources, though remaining ice
still will pose a major challenge to operations most of the year. Expectations of large
undiscovered oil and gas resources already drive the focus of the petroleum industry and
governments northwards. As marine species move northwards with warmer sea and less ice,
so will the fishing fleet. It is however hard to tell whether the fisheries will become richer or
not; fish species react differently to changes in marine climate, and it is hard to predict
whether the timing of the annual plankton blooms will match the growth of larvae and young
fish also in the future. Shipping and tourism are likely to increase, though drift ice, short
sailing seasons and lack of infrastructure will impede a fast development of transcontinental
shipping of goods; it is more likely that traffic linked to extraction of Arctic resources in the
outskirts of the northern sea routes will grow first. These activities offer new economic
opportunities. At the same time they also represent new pressures and risks to an ocean that so
far has been closed to most economic activities by the ice. This should be met by better
international regulations of these activities.
High interest in getting access to the resources in the Arctic may create tensions and security
problems. However most border issues in the Arctic Ocean have been set, giving clear rules
for who has the right to manage the resources. The coastal states of the Arctic Ocean all
follow the UN Convention of the Law of the Seas in the remaining issues of delimitation of
their Exclusive Economic Zones and extended continental shelves.
Past trends
The extent of the minimum ice cover at the end of the melt season in September 2007 broke
all previously observed records. If older ship and aircraft observations are taken into account,
sea ice coverage may have been halved since the1950s (NSIDC, 2007; Meier, 2007). Since
the more reliable satellite observations started in 1979, the summer ice has shrunk with 10,2
% per decade (Comiso 2007, NSIDC, 2007). The reduction in winter maximum extent is
smaller, with a decrease of 2,9% per decade (Figure 5.3.5.1) (Stroeve et al 2007). Both
summer and winter decline has accelerated (Comiso 2008).
The ice also gets thinner and younger since less ice survives summer and grows into thicker
multi-year floes. There is a remarkable shift in the composition of the sea ice towards less
multi-year ice and larger areas covered with first-year ice (Figure 5.3.5.3). The young ice
absorbs more heat, is weaker and has less biological life than the older ice.
Figure 5.3.5.3. The area of thick, multi year sea ice in the Arctic Ocean decreases. The figure
is based on a combination of modelling and satellite observations (Nghiem et al 2007).
Observations of thickness are more scattered, and it is hard to calculate trends for the whole
ice cover. Submarine data have been considered to be most representative and have
demonstrated a decrease of 40% from an average of 3,1 meters in 1956-78 to 1,8 meters in the
1990s (Rothrock et al 1999; UNEP 2007). British submarine data from 2007 show continued
thinning (Wadham, pers com). German observations from the area around the North Pole
indicate that ice thickness here has decreased from 2 m in 2001 to 0.9 m in 2007, both due to
a general thinning and a shift towards generally younger ice (Nghiem et al, 2007; Haas,
pers.com.) These results are in stark contrast with observations between Ellesmere Island and
86N, where ice thickness was still above 4 m in 2006 (Haas et al., 2006).
The Arctic sea ice reacts very sensitively to changes in air and ocean temperatures as well as winds,
waves and ocean currents. There are strong imprints of natural variability in the observed
changes, e.g. due to regular shifts in the circulation patterns of the polar atmosphere.
However, the changes that can be attributed to increases in greenhouse gases seem to increase
over time (Stroeve et. al., 2007).
Projections
The summer ice is very likely to continue to shrink in extent and thickness, leaving larger
areas of open waters for an extended period of time. It is also very likely that conditions for
freezing in winter will persist so the winter sea ice still will cover large areas.
The speed of change is however uncertain. Several international assessments until recently
concluded that mostly ice free late-summers may occur by the end of this century (ACIA,
2004; IPCC, 2007; UNEP, 2007). But the actual melting has been faster than the average
trends simulated by the climate models used for these assessments (Figure 5.3.5.4). New
model studies suggest that ice-free summers may occur in a much nearer future. (Winton,
2006; Holland et. al., 2006; Stroeve et. al, 2007; Maslowski, 2007). Exactly when is
impossible to predict with confidence, both due to the limited understanding of the processes
involved and the large variability of the system.
Most studies emphasize that it is very likely that a thinner and more vulnerable ice will break
up so more heat from the sun will be absorbed in the open water. This can lead to abrupt
melting and a high susceptibility to strong winds when weather conditions are favourable, like
in the summer of 2007. An increased influx of warm Atlantic and Pacific water can also be an
important mechanism for further weakening of the sea ice. Unless followed by consecutive
years of cold winters, such events will produce a thinner, younger and even more vulnerable
ice cover that can melt more easily the next summer, and more easily be transported out of the
Polar Ocean.
Figure 5.3.5.4:
The retreat of the sea ice has been faster than predicted: Arctic September sea ice extent from
observations (thick red line) and 13 IPCC AR4 climate models, together with the mean value
(solid black line) and variation (dotted black line) from several models run. (Updated from
Stroeve et al 2007).
5.3.6. Mountain Permafrost
Key Messages
• A warming of mountain permafrost in Europe of 0.5-1.0°C has been observed during the recent 1020 years.
• Present and projected atmospheric warming will lead to wide-spread thaw of mountain permafrost.
• Warming and melting of permafrost is expected to contribute to increasing the destabilization of
mountain rock-walls, the frequency of rock fall, debris flow activity and geotechnical and
maintenance problems in high-mountain infrastructure.
Presentation of the main indicator(s)
Figure 5.3.6.1: Temperature in a mountain range Figure 5.3.6.2: Temperatures measured in
containing permafrost
different boreholes at ca. 10.0 m depth
(blue colours bordered by black line)
(drilled in rock-glaciers and frozen rock-walls)
Source: Gruber (2007)
Source: PERMOS (2007)
[http://maps.grida.no/go/graphic/mountain-permafrost-patterns-and-temperature-gradients]
Relevance
Permafrost is permanently frozen ground and consists of rock or soil material that has remained at or
below 0°C continuously for more than 2 years.
Mountain permafrost is the dominating permafrost in Europe, because Arctic permafrost exists in
Europe in the in northernmost parts of Scandinavia only. He is abundant at high elevations in midlatitude mountains, where the annual mean temperature is below -3°C. It contains variable amounts of
ice and exists in different forms: in steep bedrock, in rock glaciers, in debris deposited by glaciers or in
vegetated soil. Because vegetation and circulating groundwater in the mountain permafrost area are
mostly absent, the temperature in the deeper rock material is largely determined by the history of
temperature at its surface. Therefore mountain permafrost contains valuable information on climate
change. Even if temperature profiles from alpine boreholes are difficult to interpret in terms of past
trends due to the effects of the complex topography (Fig.5.3.6.1) and the availability of insulating
snow-cover (Gruber et al., 2004), monitoring of temperature changes at depth however provides
valuable data on the thermal response of permafrost to climate change.
Permafrost influences the evolution of mountain landscapes and affects human infrastructure and
safety. Permafrost warming or thaw affects the potential for natural hazards, such as rock falls (e.g. at
the Matterhorn in summer 2003) and debris flows (Noetzli et al., 2003; Gruber and Haeberli, 2007). At
least four large events involving rock volumes over 1 million m3 took place in the Alps during the last
decade. Its effects on infrastructure have motivated the development of technical solutions to improve
design lifetime and safety (Philips et al., 2007).
Past trends
Data from a north-south transect of boreholes, 100m or more deep, extending from Svalbard to the
Alps (European PACE-project) indicate a long-term regional warming of permafrost of 0.5-1.0°C
during recent decades (Harris et al., 2003). In Scandinavia and Svalbard, monitoring over 5-7 years
show warming down to 60m depth and present warming rates at the permafrost surface of 0.040.07°C/year (Isaksen et al., 2007). In Switzerland, a warming trend and increased active-layer depths
were observed in 2003, but results varied strongly between borehole locations due to variations in
snow cover and ground properties (PERMOS, 2007). At the Murtel-Corvatsch (rock-glacier) borehole
in the Swiss Alps, the only long-term data-record (20 years), permafrost temperatures in 2001, 2003
and 2004 were only slightly below -1°C (Fig. 5.3.6.2) and were, apart from 1993 and 1994, the highest
since measurements began in 1987 (Vonder Mühll et al., 2007). Such data measured at rock-glaciers
are difficult to interpret because the subsurface thermodynamics in ice-rich frozen debris are rather
complex. Complementary and clearer signals on thawing permafrost are expected from boreholes that
were directly drilled into bedrock (e.g. Schilthorn and M. Barba Peider; Fig.:5.3.6.2). Corresponding
monitoring programs, such as PACE and PERMOS, however, have started only less than a decade
ago.
.
Projections
No specific projections on the behaviour of mountain permafrost are available yet, but changes in
mountain permafrost are likely to continue in the near future and the majority of permafrost bodies
will experience warming and/or melting. According to recent model calculations basing on the
regional climate model REMO and following the IPCC SRES-Scenarios A1B, A2 and B1, in the
Alpine region a warming up to 4°C until 2100 is projected (Jacob et al., 2007). The further rising
temperatures and melting permafrost could increasingly destabilize mountain walls and increase the
frequency of rock falls, posing problems to mountain infrastructure and communities (Gruber et al.,
2004). The warming and thaw of bedrock permafrost can sometimes be fast and failure along ice-filled
joints can occur even at temperatures below 0°C (Davies et al., 2001). Water flowing along linear
structures and the advection of heat along joint systems will further accelerate destabilisation (Gruber
and Haeberli, 2007).
Fig.: 5.3.6.4 Rock-Glacier Murtel-Corvatsch
Source: M.Phillips
Fig.: 5.3.6.3 TheMatterhorn
Source: M.Phillips
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