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Cryosphere
Part 1: The Arctic
Global Environmental Change –
Lecture 5 Spring 2015
What is the Cryosphere?
• The National Snow & Ice Data Center explains that some
places on Earth are so cold that water is a solid—ice or snow
• Scientists call these frozen places of our planet the
"cryosphere"
• The word "cryosphere" comes from the Greek word for cold,
"kryos“
• This is important because the cryosphere influences the
climate of the entire world, and it is home to people, plants and
animals
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Regions of the Cryosphere
•
•
•
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Arctic
Greenland
Antarctica
Third Pole
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Frozen Ground
Glaciers
Sea Ice
Ice Shelves and Icebergs
3
Tour of the Cryosphere
4
Basic Scientific Background
• Before examining the cryosphere in more detail, it
will be useful to examine some basic concepts
 Feedback
 Albedo
5
Feedback Mechanism
• Any process that acts to oppose or amplify changes to a
system that is in a steady state
• Feedback is a process whereby some proportion or in general,
function, of the output signal of a system is passed (fed back)
to the input
• The response is often proportional
 That is, as the system deviates more from the steady state position, the
faster the process works to counteract it
6
Homeostasis
• Property of an open system, especially living
organisms, to regulate its internal environment so as
to maintain a stable condition, by means of multiple
dynamic equilibrium adjustments controlled by
interrelated regulation mechanisms
• Term was coined in 1932 by Walter Cannon from the
Greek roots homo- (same, like) and sta- (to stand or
stay)
7
Negative Feedback
• A type of feedback, during which a system
responds so as to reverse the direction of
change
• Since this process tends to keep things
constant, it is stabilizing and attempts to
maintain homeostasis
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Negative Feedback Example –
A Ball Rolling Inside a Curved Bowl
• Initially, the ball oscillated from side-to-side, rising far up the sides of the bowl
• With time, the amplitude of the motion decreases until the ball comes to rest at
the bottom of the bowl
• Once stationary, the ball has reached a position of stability
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Positive Feedback –
Microphone Screech
• Small sounds picked up by the microphone are amplified by the nearby speaker,
where the microphone once again picks up the amplified sound and
rebroadcasts it through the speakers
• This looping continues until the initially tiny sound is re-amplified repeatedly to
a piercing squeal
10
Audio Feedback
• An example of microphone-speaker feedback
11
Nuclear Chain Reaction
12
Cybernetic Systems
• From the Greek kubernetes, meaning a
steersman
• Cybernetics means the branch of study
concerned with self-regulating systems using
communication and control in either
mechanical devices or living biological
organisms
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Cybernetic System Components
• Sensor
• Amplifier
• Controller
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Instrument vs. Man
• Cybernetic control
by electrical
system
• Cybernetic
control by
human brain
15
Albedo
• Albedo is the fraction of solar energy (shortwave
radiation) reflected from the Earth back into space
• It is a measure of the reflectivity of the earth's surface
16
Effect of Albedo Change
• Ice, especially with snow on top
of it, has a high albedo: most
sunlight hitting the surface
bounces back towards space
• Water is much more absorbent
and less reflective
• So, if there is a lot of water, more
solar radiation is absorbed by the
ocean than when ice dominates
17
Seasonal Importance of Albedo
• Albedo is not important at high
latitudes in winter: there is hardly
any incoming sunlight to worry
about
• It becomes important in spring
and summer when the radiation
entering through leads can greatly
increase the melt rate of the sea
ice
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Ice Albedo Feedback
• Ice with snow cover has a high albedo of about
0.9, meaning that 90% of incident radiation is
reflected into space – there is little heating of the
ground
• Bare ice absorbs about 50% of the incident
radiation
• Open ocean absorbs 94%
• As ice melts, more and more heat is retained,
creating a positive feedback
19
Ice-Albedo Feedback Summary
• The Ice-Albedo feedback can work in reverse
• If climate starts to cool, snow accumulates, turns to ice, and
reflects more light back into space
• This further cools the surface and the air above it
• Either in forward or reverse, ice-albedo is a positive feedback,
amplifying the input perturbation
20
High-Latitude Climate Sensitivity
• The high latitudes, particularly the Arctic, are predicted by all
the Global Circulation Models to be much more sensitive to
climate change then the temperate and tropical regions
• This is currently observed
• It is largely a result of the ice-albedo feedback
• It is estimated that the Arctic will see 2-4 times the as much
warming as the global average
• Sea ice changes have a very obvious effect on the large
changes climate changes seen in the Greenland ice cores
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2012 Temperature Data
22
Arctic Feedbacks
• Feedback mechanisms in the Arctic are of growing concern
• In 2009, the World Wildlife Federation published a well written report
entitled “Arctic Climate Feedbacks: Global Implications” edited by Martin
Sommerkorn & Susan Joy Hassol – a link to the PDF version of the second
edition is on the Activity Sheet
• While WWF is an advocacy group, this report was written by research
scientists (see pp. 93-96 of the report), and was mentioned by Professor
Ricky Rood of the University of Michigan in a blog dated October 1, 2009
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Impact on Northern Hemisphere
• Amplification of global warming in the Arctic will have fundamental impacts
on Northern Hemisphere weather and climate
• Due to the sun’s rays striking the Earth’s surface more directly at the equator
than at the poles, there is an inequality in the amount of solar radiation
received at the poles and the equator, which gives rise to a gradient in
atmospheric temperatures, driving circulation of air in the atmosphere
• This transports heat from regions of low-latitude warmth to the cooler poles,
heat which is then radiated to space
• Because of this transport, poleward of about 38º in each hemisphere, the
Earth emits more radiation to space (as longwave radiation) than it receives
from the sun as shortwave radiation
24
Heat Transport
• Much of the atmospheric heat
transport is accomplished by
weather systems travelling
along the wavy jet streams of
the middle and higher latitudes
in each hemisphere (red
arrows)
25
Sea-Ice Modification
•
•
•
•
•
Arctic sea-ice cover modifies the basic temperature gradients from the equator to
the poles and hence the manner in which the atmosphere transports heat
Sea ice influences temperature gradients because of its high reflectivity and its role
as an insulating layer atop the Arctic Ocean
At its maximum seasonal extent in spring, when it covers an area roughly twice the
size of the continental United States, the albedo of the freshly snow covered ice
surface may exceed 80 per cent, meaning that it reflects more than 80 per cent of
the sun’s energy back to space and absorbs less than 20 per cent
By September, the ice cover shrinks to about half of its spring size
While summer melting causes the albedo of the ice pack to decrease to about 50 per
cent through exposing the bare ice and the formation of melt ponds, this is still
much higher than that of the ocean and land areas, which may have albedos of less
26
than 10 per cent
Climate Stabilization
• When arctic sea-ice melts, it absorbs a lot of energy, and keeps the air
temperature from rising
• Sea-ice is also a good insulator – from October through April, it covers
much of the Arctic ocean, greatly slowing the rate of heat loss to the
atmosphere
• As ice cover diminishes, the insulating effect is also diminished, allowing
the Arctic atmosphere to warm in winter
• This has important climate implications
27
Ice Margin
• As the figure shows, the ice
margin is characterized by
particularly strong
temperature gradients
during winter
• This favors the development
of low pressure systems
along the edge of the ice
28
Polar Vortex
•
•
A persistent, large-scale cyclone located near either of a planet's geographical poles
is called a polar vortex
On Earth, the polar vortices are located in the middle and upper troposphere and the
stratosphere
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They surround the polar highs and lie in the wake of the polar front
These cold-core low-pressure areas strengthen in the winter and weaken in the summer due to their
reliance upon the temperature differential between the equator and the poles
The term is not new, dating back at least as far as 1853
When the polar vortex is strong, the Westerlies increase in strength
When the polar cyclone is weak, the general flow pattern across mid-latitudes
buckles and significant cold outbreaks occur
Ozone depletion occurs within the polar vortex, particularly over the Southern
Hemisphere, and reaches a maximum in the spring
29
Arctic Amplification
•
•
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Depictions from the NCAR
CCSM3 global climate model of:
(a) near surface (2 meter)
temperature deviations by month
and year over the Arctic Ocean
Deviations are relative to 19792007 average
The simulation uses the IPCC A1B
emissions scenario for this century
and observed greenhouse gas
concentrations for the 1990s
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Arctic Atmospheric Temperature
• Latitude by height plot of
October-March temperature
deviations for 2050-2059
• Deviations are relative to 19792007 average
• The simulation uses the IPCC
A1B emissions scenario for this
century and observed greenhouse
gas concentrations for the 1990s
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Future Warming
32
Static Stability and Atmospheric Thickness
• Atmospheric heating over the Arctic Ocean through a
considerable depth will alter both the change in temperature
with elevation (known as the atmosphere’s static stability) and
the gradient of atmospheric thickness from the equator to the
poles
• Atmospheric thickness is the separation, in meters, between
two adjacent pressure levels in the atmosphere, and it increases
with increasing atmospheric temperature
33
Weather Changes
• A weak thickness gradient toward the poles, will weaken the
vertical change in wind speed, called the wind shear
• Warming the Arctic atmosphere will decrease the thickness
gradient between the poles and the equator
• Changes in the static stability and atmospheric thickness
gradient will affect the development, tracks and strengths of
weather systems, and the precipitation that they generate
34
North Atlantic Oscillation
• The NAO describes a correlation in the strengths of the
Icelandic Low (the semipermanent low pressure cell centered
near Iceland) and the Azores High (the semipermanent high
pressure cell centered near the Azores) — the major
atmospheric “centers of action” in the North Atlantic.
• When both centers are strong (a deep low and a strong high),
the NAO is in its positive phase
• When both centers are weak (a shallow low and a weak high),
the NAO is in its negative phase
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NAO Diagram
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NAO Variation
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Polar Vortex Breakdown
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.
38
January, 2014
•
Regions of light blue color show the "wavy"
counter-clockwise path of the jet stream for
January 6, 2014. U.S. is near bottom center
•
Regions of light blue color show a
more circular flow for the jet stream
during the period December 15-17,
2013.
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February 26, 2014
Winds at a height where the pressure is 250 mb
show the axis of the jet stream, seen here at 00
UTC February 26, 2014. A sharp trough of low
pressure was present over the Eastern U.S., and
unusually strong ridges of high pressure were
over the Western U.S. and the North Atlantic.
Great Lake ice cover as seen on February 19, 2014, by the
MODIS instrument on NASA's Aqua satellite. Ice cover on
North America’s Great Lakes reached 88 percent in midFebruary 2014—levels not observed since 1994. The average
maximum ice extent since 1973 is just over 50 percent. It has
surpassed 80 percent just five times in four decades. The lowest
average ice extent occurred in 2002, when only 9.5 percent of
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the lakes froze. Image credit: NASA Earth Observatory.
Arctic Oscillation (AO) Index
• The Arctic Oscillation refers to an opposing pattern of pressure
between the Arctic and the northern middle latitudes
 Overall, if the atmospheric pressure is high in the Arctic, it tends to be low in
the northern middle latitudes, such as northern Europe and North America
 When pressure is high in the Arctic and low in mid-latitudes, the Arctic
Oscillation is in its negative phase
 In the positive phase, the pattern is reversed
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Arctic OscillationDiagrams
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Snowmageddon
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Heavy Snowfall = No Climate Warming?
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•
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Global warming skeptics regularly have a field day whenever a record snow storm
pounds the U.S., claiming that such events are inconsistent with a globe that is
warming
If the globe is warming, there should, on average, be fewer days when it snows, and
thus fewer snow storms
However, it is possible that if climate change is simultaneously causing an increase
in ratio of snowstorms with very heavy snow to storms with ordinary amounts of
snow, we could actually see an increase in very heavy snowstorms in some portions
of the world
There is evidence that this is happening for winter storms in the Northeast U.S.--the
mighty Nor'easters like the "Snowmageddon" storm of February 5-6 and
"Snowpocalypse" of December 19, 2009.
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Evidence
• There are two requirements for a record snow storm:
 1) A near-record amount of moisture in the air (or a very
slow moving storm).
 2) Temperatures cold enough for snow.
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Groisman Study
• Groisman et al. (2004) found a 14% increase in heavy (top
5%) and 20% increase in very heavy (top 1%) precipitation
events in the U.S. over the past 100 years, though mainly in
spring and summer
• They did find a significant increase in winter heavy
precipitation events have occurred in the Northeast U.S.
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Changnon Study
• Changnon et al. (2006) found, "The temporal distribution of
snowstorms exhibited wide fluctuations during 1901-2000,
with downward 100-yr trends in the lower Midwest, South,
and West Coast. Upward trends occurred in the upper
Midwest, East, and Northeast, and the national trend for 19012000 was upward, corresponding to trends in strong cyclonic
activity."
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2009-2010
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Lake Effect Snow
• A study by Kunkel et al. (2008) noted that we should expect
an increase in lake-effect snowstorms over the next few
decades
• Lake-effect snow is produced by the strong flow of cold air
across large areas of relatively warmer ice-free water
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Kunkel Study
• The report says, "As the climate has warmed, ice coverage on the Great
Lakes has fallen. The maximum seasonal coverage of Great Lakes ice
decreased at a rate of 8.4 percent per decade from 1973 through 2008,
amounting to a roughly 30 percent decrease in ice coverage. This has
created conditions conducive to greater evaporation of moisture and thus
heavier snowstorms. Among recent extreme lake-effect snow events was a
February 2007 10-day storm total of over 10 feet of snow in western New
York state. Climate models suggest that lake-effect snowfalls are likely to
increase over the next few decades. In the longer term, lake-effect snows
are likely to decrease as temperatures continue to rise, with the
precipitation then falling as rain".
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South Haven, Michigan 01-08-14
• Cold wave and winter
weather associated with the
Midwest and Eastern U.S.
"Polar Vortex" episode of
January 5 - 8, 2014, cost an
estimated $3 billion
• Snow shovelers take a
break in South Haven,
Michigan after an epic lake
effect snowstorm buried
the city on January 8, 2014
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February 15, 2015
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What Effect DO NAO Changes Have?
• The WWF Federation report summarizes the changes do to
positive and negative NAO cycles as follows:
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The Arctic and Carbon
• Increasing attention has been responses of various
regions to increasing carbon levels in the atmosphere
 Carbon sinks are regions that absorb more carbon dioxide
from the atmosphere than they emit
 Carbon sources are regions that emit more carbon dioxide
from the atmosphere than they absorb
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Carbon Dioxide Solubility
• CO2 is more soluble in cold water than warm
• The exchange of gases, such as carbon dioxide, between the atmosphere
and ocean is primarily controlled by:
 Gas concentration differences between the air and the sea
 The turbulence in the lower atmosphere, which arises from weather patterns and longerterm climate changes that control the variability of wind and waves
• In polar seas, seasonal or permanent sea-ice cover is a potential barrier to
the atmosphere-ocean exchange of gases compared to open waters
elsewhere
55
Arctic Carbon Sink
• Recent analyses indicate that surface waters of the Arctic
Ocean generally have low to very low carbon dioxide
concentrations, compared to its concentration in the
atmosphere
• As such, these surface waters have the ability to absorb large
amounts of carbon dioxide, about 0.066 to 0.175 gigatonnes
(GT) of carbon per year
56
Carbon Uptake
• In the shallow coastal waters of the Chukchi and Barents seas, the inflow of
nutrient-rich seawater from the Pacific and Atlantic oceans, coupled with the
seasonal retreat and melting of sea ice and the abundance of light, sustains high
rates of marine plant (i.e., phytoplankton) photosynthesis and growth in open
waters each year.
• The seasonal growth of marine phytoplankton and zooplankton (e.g., shrimp,
copepods) supports rich and diverse open-water and seafloor ecosystems
• These ecosystems provide critical food sources for marine mammals (e.g., grey
whale, walrus, polar bears), seabirds and human populations in the Arctic
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Carbon Inventory
•
•
•
•
The upper waters of the Arctic contain approximately 25 GT of inorganic carbon
and about 2 GT of organic carbon (in the form of living organisms, detritus and
other materials)
Seawater inflow of Pacific Ocean water through Bering Strait into the Chukchi Sea
and Atlantic Ocean water flowing into the Barents Sea supplies an inflow of about 3
GT of inorganic carbon per year into the Arctic Ocean with a similar outflow from
the Arctic through Fram Strait
Within the Arctic itself, river inputs and coastal erosion constitute a land to ocean
carbon flux of about 0.012 GT of carbon per year
However, there are larger uncertainties about the atmosphere-ocean fluxes of carbon
and production of organic carbon by marine plant photosynthesis and its subsequent
export from surface waters to deep waters and sediments of the Arctic
58
Arctic Vulnerability
• The potential vulnerability of the marine carbon cycle due to natural and
human caused climate-change factors include:
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Sea-ice loss, warming, circulation and other physical changes
Changes in biology and ecosystem structure of the Arctic
Changes in the water cycle and freshwater inputs to the Arctic Ocean
Ocean acidification effects
• Of these factors, sea-ice loss, phytoplankton growth, and warming appear
to be the primary agents of change over the next decade or so
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Short Term Effects
• Because exposed surface waters have a lower carbon dioxide
content than the atmosphere, sea-ice loss is expected to
increase the uptake of carbon dioxide by surface waters
• The loss of sea-ice effectively removes the barrier to the
atmosphere-ocean exchange of gases, including
 Carbon dioxide
 Methane
 Dimethylsulfide, emitted to the atmosphere by marine phytoplankton
• Affects cloud formation
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Present State of C in the Arctic
• At present, the Arctic Ocean is a globally important net sink, responsible
for the 5 to 14 per cent of the global ocean’s net uptake of carbon dioxide
• Some estimates say this may increase to 18% in the short term
• This masks the global reduction of the ocean uptake of carbon dioxide over
the last few decades and, thus, is increasingly important to the feedback
between the global carbon cycle and climate
61
Future Predictions
• Over time, in response to environmental changes driven
largely by climate and environmental change, changes will
occur in:
 carbon and carbon dioxide distributions in surface and subsurface waters,
 atmosphere-ocean carbon dioxide gradients,
 the capacity of the Arctic Ocean to uptake carbon dioxide
• This makes future predictions of the Arctic Ocean carbon
dioxide sink/source trajectory beyond the next decade difficult
62
Longer Term Effects
• Reduced cooling of water during its movement to the poles and increased
absorption of the sun’s energy that results in the warming of surface water
relative to previous decades should act to increase the carbon dioxide
content of seawater toward the saturation limit
• In the recent past (1998-2006), warming of up to 2°C had been observed in
the regions of significant sea-ice loss (mainly on the “inflow” arctic shelves
such as the Chukchi and Barents seas)
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Competing Effects
• If surface waters warm by 4 to 5°C, as a consequence of climate change
predicted by the end of this century, and if present-day carbon and carbon
dioxide distributions remain unchanged, the Arctic Ocean carbon dioxide
sink will significantly decrease in size as a result of warming
• While the impacts of sea-ice and increased phytoplankton photosynthesis
and growth will continue to use up carbon dioxide in the water, the
saturation of carbon dioxide in warmer waters may somewhat counteract
these effects on the atmosphere-ocean exchange of carbon dioxide
• As a result of future climate change, ecosystem shifts may affect the export
of organic carbon and decrease interactions between the pelagic (open
ocean) and benthic (seafloor) ecosystems
64
Arctic Ocean
Geography
• The coastal seas of the Arctic (Barents,
Laptev, Kara, East Siberian, Chukchi
and Beaufort seas) overlie shallow
continental shelves (less than 200
meters deep) that constitute about 53
per cent of the total area of the Arctic
Ocean
• The remainder is a deep central basin
more than 2,000 meters deep, flanked
by the slightly shallower Eurasian and
Canada basins
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Surface vs. Deep Water
• In the central basin of the Arctic, subsurface waters are relatively isolated
from surface waters due to differences in seawater density that change with
depth and limited exchanges with deep water outside of the Arctic
• As such, climate change due to warming, sea-ice loss and other processes
mostly affects surface waters rather than the deep, isolated and old subsurface
waters in the central basin
• In the central basin, density stratification generally acts as a barrier to mixing
between nutrient-poor surface waters and nutrient-rich subsurface waters
 Subsurface waters generally have much higher carbon dioxide content than surface waters,
with low rates of mixing between these waters and the surface mixed layer
 The surface mixed layer typically extends to 10 to 50 meters, with depth heavily dependent
on mixing due to winds and sea-ice cover
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Mixing in the Arctic
• The loss of sea-ice should facilitate deeper mixing and bring
nutrient and carbon dioxide-rich subsurface waters to the
surface
• This could either increase or decrease atmosphere-ocean
carbon dioxide exchanges depending on biological responses
of the Arctic Ocean surface ecosystem to the increased supply
of nutrients
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Fresh Water in the Arctic
• Melting sea-ice is introducing large amounts of cold fresh water in the
Beaufort Gyre, with possible climatic consequences
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Acidification in the Arctic
• The predicted ocean uptake of human-caused carbon dioxide,
based on IPCC scenarios, is expected to increase hydrogen ion
concentration by 185 per cent and decrease its pH by 0.3 to 0.5
units over the next century and beyond, with the Arctic Ocean
impacted before other regions as a result of the relatively low
pH of polar waters compared to other waters
• In the Arctic Ocean, potentially corrosive waters are found in
the subsurface layer of the central basin
69
Terrestrial Carbon
• The largest deposits of organic carbon of any region on Earth are contained
in the Arctic
• Arctic terrestrial ecosystems play an important role in the global carbon
cycle, making large contributions to fluxes of the greenhouse gases carbon
dioxide and methane
• Both outflows of carbon from and inflows of carbon to Arctic terrestrial
ecosystems have been altered as climate has warmed
• As warming continues in the future, carbon emissions from Arctic lands are
projected to outpace uptake, further adding to global warming
70
• Arctic terrestrial
ecosystems make an
important contribution to
terrestrial carbon fluxes
Carbon Fluxes
 They remove about 0.3 to 0.6
GT of carbon per year
 They add about 0.03 to 0.1 GT
of methane to the atmosphere
 They contribute relatively
smaller but still significant
carbon export as dissolved
organic matter into arctic rivers
and eventually into the oceans
71
Source of Terrestrial C
• Carbon was deposited over millennia of slow growth by mosses, grasses
and woody plants
• As these plants decayed to litter and eventually to soil carbon, there was
little release of the stored carbon to the atmosphere as a result of prevalent
low temperatures that did not allow microorganisms to break down the
organic matter
• The result was a slowly growing deposit of carbon that over many
millennia became one of the largest deposits on Earth
• Most of these carbon deposits are presently locked away from the
atmosphere in frozen ground and so are not contributing significantly to the
buildup of atmospheric greenhouse gases
72
C Storage on Earth
Region
C in Vegetation, GT
C in Soils, GT
Arctic
60-70
1650
Temperate Zone
139
262
Tropics
340
692
• Arctic means the northern circumpolar permafrost region
• For comparison, the carbon content of Earth's atmosphere has increased
from ∼360 GT during the last glacial maximum to ∼560 GT during
preindustrial times and ∼730 GT in 2006
• In 2006, the total earth C estimate in solids was 1500 GT
73
Yedomo
•
•
•
(Left) Exposed carbon-rich soils from the mammoth steppe-tundra along the Kolyma River in
Siberia. The soils are 53 m thick; massive ice wedges are visible
(Right) Soil close-up showing 30,000-year-old grass roots preserved in the permafrost
Yedoma represents relict soils of the mammoth steppe-tundra ecosystem which contain little
of the humus that characterizes modern ecosystems of the region, but they comprise large
amounts of grass roots and animal bones, resulting in a carbon content that is much higher than
is typical of most thawed mineral soils
74
C Release from Yedomo
• Organic matter in yedoma decomposes quickly when thawed, resulting in
respiration rates of initially 10 to 40 g of carbon per m3 per day, and then
0.5 to 5 g of carbon per m3 per day over several years
• If these rates are sustained in the long term, as field observations suggest,
then most carbon in recently thawed yedoma will be released within a
century, a striking contrast to the preservation of carbon for tens of
thousands of years when frozen in permafrost
75
Local Thawing
• Some local thawing of yedoma occurs independently of climate change
• When permafrost ice wedges thaw, the ground subsides, forming
thermokarst lakes
• Abundant thermokarst lakes on yedoma territory migrate across the plains
as thawing and subsidence occur along their margins
• During the Holocene (the past 10,000 years), about half of the yedoma
thawed beneath these migratory lakes and then refroze when the lakes had
moved on
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Methane Production
• The yedoma carbon beneath the thermokarst lakes is decomposed by
microbes under anaerobic conditions, producing methane that is released to
the atmosphere primarily by bubbling
• Near eroding lake shores, methane bubbling is so high that channels
through the lake ice remain open all winter
• During a thaw/freeze cycle associated with lake migration, ∼30% of
yedoma carbon is decomposed by microbes and converted to methane
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Release of C to Surface Waters
• In a 2013 PNAS article, Cory et al. conclude that recent
climate change, by increasing arctic soil temperatures and
thawing large areas of permafrost, allows for microbial
respiration of previously frozen C
• They also find soil destabilization from melting ice has caused
an increase in thermokarst failures that expose buried C and
release dissolved organic C (DOC) to surface waters, and that,
once exposed, the fate of this C is unknown but will depend on
its reactivity to sunlight and microbial attack, and the light
available at the surface78
C Release from Frozen Soil
• It is clear that the rate of C release from frozen soils is a critical issue
• Permafrost thaw and the microbial decomposition of previously frozen
organic carbon is considered one of the most likely positive climate
feedbacks from terrestrial ecosystems to the atmosphere in a warmer world
• Knowledge of C release rates from permafrost soils are crucial for
predicting the strength and timing of this carbon-cycle feedback effect
• Sustained carbon transfers to the atmosphere must come from old carbon,
which forms the bulk of the permafrost carbon pool that accumulated over
thousands of years
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Schuur et al. Study
• Schuur et al. (2009) found that areas that thawed over the past 15 years had
40 per cent more annual losses of old carbon than minimally thawed areas,
but had overall net ecosystem carbon uptake as increased plant growth
offset these losses
• However, areas that thawed decades earlier, lost significantly more old
carbon, a 78 per cent increase over minimally thawed areas
• Old carbon loss contributed to overall net ecosystem C release despite
increased plant growth
• “Our data document significant losses of soil carbon with permafrost thaw
that, over decadal timescales, overwhelms increased plant carbon uptake at
rates that could make permafrost a large biospheric carbon source in a
80
warmer world”
Eight-Mile Lake Study Site
•
•
•
Infrared air photo of the Eight Mile Lake study site and
surrounding area
Ground subsidence as a result of permafrost thaw and ice
wedge melting is visible as dark striations that occur at the
study site and the surrounding hillslopes
Symbols represent the location of the extensive thaw site
(black), the moderate thaw site adjacent to the borehole
(grey), and the minimal thaw site (white).
81
Early-Season Permafrost
• Early-season photo of
extensive permafrost
thaw showing ground
subsidence and water
ponding
• Due to the shallow thaw
at this time of year, the
water table is still
visible at the soil surface
82
Mid-season
•
•
•
Water table drops below the soil surface
as the seasonal thaw depth increases
Tundra dominated by shrubs following
permafrost thaw is visible in the
foreground
Minimally-subsided tundra dominated by
the tussock forming sedge, Eriophorum
vaginatum, is visible in the far
background as the light green vegetation
in the left middle of the photo
83
Estimating C Age
•
•
•
“At monthly intervals during the growing season, we also collected ecosystem
respiration CO2 from dark chambers, as well as soil CO2 from soil profile gas wells,
for Δ14C analysis
In the laboratory, CO2 was then purified and analyzed for Δ14C using an accelerator
mass spectrometer, while a subsample was analyzed for δ13C using an isotope ratio
mass spectrometer.
Radiocarbon provides an indication of the age of respired C, and thus can be used
as a fingerprint for identifying the decomposition of old organic C that has been
stored in these permafrost soils”
84
Thawing Permafrost Video
85
Schuur et al. Figure
• Net exchange of CO2 between tundra and the atmosphere for three sites
that differ in the extent of permafrost thaw
86
Arctic Tipping Points
• The Sommerkorn and Hassol WWF study concluded that the arctic carbon
cycle will undergo one of the biggest transformations of any region, with
consequences for fluxes of carbon, nutrients, energy and water, for vegetation
and biodiversity, and for interactions between the Arctic and global climate
• They say many changes will unfold rapidly with immediate effects on the
function and structure of the Arctic
 For example, disturbances driven by warmer and drier conditions have the
potential to lead to rapid changes and tipping points
 Increased damage by insect attacks and fires have already tipped the C balance in
parts of Canada, changing it from a small C sink to a net C source in just a decade
87
Sea Ice Decline
• Sea ice has been declining steadily, if
irregularly, since the beginning of
satellite data availability
• Numerous changes in climate
behavior have been noted
• While it is not yet possible to clearly
link each change to the melting of
Arctic sea ice, a causal link is
suspected
• The next slide shows an animation of
sea ice changes
88
Sea Ice Animation
Sea Ice motion over the Arctic Basin.
Sea ice shows up as various shades of
grey and open ocean as blue. Each
image is a snapshot of sea ice cover
each day with the date shown in the
lower part of each image.
In general lighter shades of grey are
newly formed first year ice and the dark
shades of grey are older multi-year ice.
The motion of large ice floes and the
formation leads can be seen quite well
during the winter months.
89
Major Changes: 2007
• The Arctic sea-ice extent set a record minimum in September, with a
dramatic reduction in area of coverage (4.3 million km2)
• Cariboo populations that have been increasing at a steady rate since the
early to mid 1970's are either showing signs of peaking or beginning to
decline
• The last five years (to 2004) were characterized by an increase of total river
discharge to the Arctic Ocean mainly due to a contribution from Asian
rivers, with a mean 2000-2004 discharge from Asia was 110 km3 (5%)
higher than over the previous twenty years.
90
Major Changes: 2008
•
•
•
Autumn temperatures are at a record 5º
C above normal, due to the major loss of
sea ice in recent years which allows
more solar heating of the ocean
Winter and springtime temperatures
remain relatively warm over the entire
Arctic, in contrast to the 20th century
and consistent with an emerging global
warming influence
Arctic-wide annual averaged surface air
temperature anomalies (60°–90°N)
based on land stations north of 60°N
relative to the 1961–90 mean
91
Major Changes: 2008 continued
•
•
•
•
•
During 2008 the summer minimum ice extent, observed in September, reached 4.7
million km2
While slightly above the record minimum of 4.3 million km2, set just a year earlier
in September 2007, the 2008 summer minimum further reinforces the strong
negative trend in summertime ice extent observed over the past thirty years
At the record minimum in 2007, extent of the sea ice cover was 39% below the
long-term average from 1979 to 2000
Arctic sea ice cover is composed of perennial ice (the ice that survives year-round)
and seasonal ice (the ice that melts during the summer)
Consistent with the diminishing trends in the extent and thickness of the cover is a
significant loss of the older, thicker perennial ice in the Arctic
92
Major Changes: 2008 continued
•
•
•
Data from the NASA QuikSCAT launched in 1999 and a buoybased Drift-Age Model indicate that the amount of perennial ice
in the March ice cover has decreased from approximately 5.5 to
3.0 million km2 over the period 1958–2007
Many authors have recently acknowledged that a relatively
younger, thinner ice cover is more susceptible to the effects of
atmospheric and oceanic forcing
In the face of the predictions for continued warming
temperatures, the persistence of recent atmospheric and oceanic
circulation patterns, and the amplification of these effects
through the ice albedo feedback mechanism, it is becoming
increasingly likely that the Arctic will change from a
perennially ice-covered to an ice-free ocean in the summer.
93
Major Changes: 2008 continued
•
•
•
•
Sea Surface Temperature (SST ) trends over the past
100 years in the Arctic marginal seas were analyzed
by Steele et al. (2008)
They found that many areas cooled up to ~0.5°C
decade–1 during 1930–65 as the Arctic Oscillation
(AO) index generally fell, while these areas warmed
during 1965–95 as the AO index generally rose
Warming is particularly pronounced since 1995, and
especially since 2000 when the AO index exhibited
relatively low and fluctuating values
Summer 2007 satellite-derived data indicate that
SST anomalies were up to 5°C in ice-free regions
94
Major Changes: 2009
•
•
One of the most dramatic signals of the general Arctic-wide warming trend
in recent years is the continued significant reduction in the extent of the
summer sea ice cover and the decrease in the amount of relatively older,
thicker ice
The extent of the 2009 summer sea ice cover was the third lowest value of
the satellite record (beginning in 1979) and >25% below the 1979 - 2000
average
95
Major Changes: 2009 continued
• In 2008, there was an unprecedented amount of fresh water in
the surface layer of the Arctic Ocean
• The source of the fresh water was melting sea ice
• The heating of the ocean in areas of extreme summer sea ice
loss (for instance, summer surface water temperatures in the
Beaufort Sea were more than 3°C above average) was
contributing to record high surface air temperatures in the fall
(October through December) over the Arctic Ocean.
96
Major Changes: 2010
•
•
•
•
•
A combination of low winter snow accumulation and warm spring temperatures created a new
record low spring snow cover duration over the Arctic in 2010, since satellite observations began in
1966
Glaciers and ice caps in Arctic Canada are continuing to lose mass at a rate that has been increasing
since 1987, reflecting a trend towards warmer summer air temperatures and longer melt seasons.
Observations show a general increase in permafrost temperatures during the last several decades in
Alaska, northwest Canada, Siberia and Northern Europe, with a significant acceleration in the
warming of permafrost at many Arctic coastal locations during the last five years.
The greatest changes in vegetation are occurring in the High Arctic of Canada and West Greenland
and Northern Alaska, where increases in greening of up to 15% have been observed from 1982 to
2008.
In the Eurasian river drainage basins, the correlation between increased river discharge and
decreased summer minimum sea ice extent (over the period 1979-2008) is greater than the
correlation between precipitation and runoff, suggesting that both rivers and sea ice were
responding to changes in large-scale hemispheric climate patterns.
97
Major Changes: 2010 continued
•
•
•
•
Panels illustrate the substantial loss in
the oldest ice types within the Arctic
Basin in recent years compared to the
late 1980s
Following the summer melt of 2007,
there was a record low amount of
multiyear ice in March 2008
Since then there has been a modest
increase in multiyear ice in 2009 and
again in 2010
Even with this increase, 2010 had the
third lowest March multiyear ice extent
since 1980
98
Major Changes: 2011
•
•
•
•
In 2011, annual near-surface air temperatures over much of the ocean were
approximately +1.5 °C greater than the 1981-2010 baseline period and land
temperatures were also above their baseline values
This continued a decade-long warm-bias of the Arctic relative to mid-latitudes
The wintertime increase and the summertime decrease in cloudiness resulted in
greater energy flux to the surface, potentially contributing to the near record low
sea ice extent this year
Below-average snow extent during spring 2011 is consistent with a decline
observed since the 1970s, and continues an accelerated decrease since 2006. June
snow cover extent in Eurasia was the lowest since the start of the satellite record in
1966
99
Major Changes: 2011continued
• Sea ice and ocean observations over the past decade (2001-2011) suggest
that the Arctic Ocean climate has reached a new state with characteristics
different than those observed previously
• The new ocean climate is characterized by less sea ice (both extent and
thickness) and a warmer and fresher upper ocean than in 1979-2000
• The persistence of these changes is having a measureable impact on Arctic
marine and terrestrial ecosystems
• An anticyclonic (clockwise) wind-driven circulation regime has dominated
the Arctic Ocean for at least 14 years (1997-2011), in contrast to the typical
5-8 year pattern of anticylonic/cyclonic circulation shifts observed from
1948-1996
100
Major Changes: 2012
• A new record low June snow cover extent (SCE) for the Northern
Hemisphere (when snow cover is mainly located over the Arctic) was set in
2012
 A new record low May SCE was also established over Eurasia
• 2012 spring snow cover duration was the second shortest on record for both
the North American and Eurasian sectors of the Arctic because of earlier
than normal snow melt
 The rate of loss of June snow cover extent between 1979 and 2012 (-17.6% per decade
relative to the 1979-2000 mean) is greater than the loss of September sea ice extent
(-13.0% per decade) over the same period
101
Major Changes: 2012 continued
•
•
•
•
•
Over the past 30 years (1982-2011), the Normalized Difference Vegetation Index
(NDVI), an index of green vegetation, has increased 15.5% in the North American
Arctic and 8.2% in the Eurasian Arctic
In the more southern regions of Arctic tundra, the estimated aboveground plant
biomass has increased 20-26%
Increasing shrub growth and range extension throughout the Low Arctic are related
to winter and early growing season temperature increases
Growth of other tundra plant types, including graminoids and forbs, is increasing,
while growth of mosses and lichens is decreasing
Increases in vegetation (including shrub tundra expansion) and thunderstorm
activity, each a result of Arctic warming, have created conditions that favor a more
active Arctic fire regime
102
Major Changes: 2012 continued
•
Massive phytoplankton blooms beneath a 0.8-1.3 m thick, fully consolidated (yet
melt-ponded) sea ice pack were observed in the north-central Chukchi Sea in July
2011

•
New satellite remote sensing observations show:



Blooms extended >100 km into the ice pack and biomass was greatest (>1000 mg C m-3) near the iceseawater interface, with nutrient depletion to depths of 20-30 m.
(a) the near ubiquity of ice-edge blooms across the Arctic and the importance of seasonal sea ice
variability in regulating primary production
(b) a reduction in the size structure of phytoplankton communities across the northern Bering and
Chukchi seas during 2003-2010
A unique marine habitat containing abundant algal species in so-called "melt holes"
was observed for the first time in perennial sea ice in the central Arctic Ocean
103
Major Changes: 2012 continued
• In 2012, new record high temperatures at 20 m depth were measured at
most permafrost observatories on the North Slope of Alaska and in the
Brooks Range, where measurements began in the late 1970s
• A common feature at Alaskan, Canadian and Russian sites is greater
warming in relatively cold permafrost than in warm permafrost in the same
geographical area
• During the last fifteen years, active-layer thickness has increased in the
Russian European North, the region north of East Siberia, Chukotka,
Svalbard and Greenland.
104
Major Changes: 2013
•
•
•
•
•
The summer 2013 mean sea level pressure field was characteristic of a positive
Arctic Oscillation/North Atlantic Oscillation
Consequently, relative to the previous six years, air temperatures were anomalously
low across the central Arctic Ocean, Greenland and northern Canada
In contrast, summer 2013 in Alaska was one of the warmest on record
Northern Hemisphere spring snow cover extent (SCE) was lower than the historical
mean (1967-2013) during 2013, with a new record low May SCE established for
Eurasia. North American June SCE was the fourth lowest on record
The record-setting loss of Eurasian spring snow cover in May 2013, and the below
normal June SCE in North America was driven by rapid snow melt, rather than
anomalously low snow accumulation prior to melt onset
105
Arctic Report Card, 2013
106
Major Changes: 2014
• Evidence is emerging that Arctic warming is driving
synchronous pan-Arctic responses in the terrestrial and marine
cryosphere. For the period 1979-2014, satellite observations
showed reductions in Northern Hemisphere snow cover extent
in May and June (-7.3% and -19.8% per decade, respectively)
bracket the rate of summer sea ice loss (-13.3% per decade in
minimum ice extent) and since 1996 the June snow and
September sea ice signals have been more coherent.
107
Arctic Surface Temperatures
• The annual surface air
temperature anomaly (+1.0°C
relative to the 1981-2010
mean value) for October
2013-September 2014
continues the pattern of
increasing positive anomalies
since the late 20th Century.
108
Arctic Report Card, 2014
109
Permafrost Peril
• Coastal house in Alaska
110
A
Potentially
Scary
Picture
• Data from March 12,
2014
• Gray shading is 2 sigma
standard deviation from
1981-2010 average
111
One Week
Later
• Data from March
19, 2014
112
3-11-15
• The gray region shows
the 2σ deviation, with a
95.4% probability
• Arctic ice is currently
well below the 30 year
2σ range – this is
somewhere between
95.4% and 99.7%
probability
113
3-18-15
• Still below the
2σ range
114
3-25-15
• Slight increase since last
week
• Barely below the 2σ
range
115