Arctic Sea Ice Climate Change

NUM. 0055 AÑO 24 JUNE 2024
Climate change is affecting
the Arctic more
than any other place on
Earth.
Arctic Sea Ice
Rdm Léenos
RDM Revista
Climate Change
@Rdm_revista
RDM Revista
www.rdmrevista.com.m

Letter to the reader.
RDM and Multimedia Magazine: This publication aims to
publicize the activity of the National Snow and Ice Data
Center (NSIC) in the collection of data from the Airborne
Snow Observatory (ASO) of the NSIDC DAAC includes
the snow depth studies as well as NASA in collecting hyperspectral
and lidar data from the melting Arctic ice cap,
each for their contribution in making the information available
for the dissemination of this publication. As well as
the collaboration for the preparation and monitoring by the
RDM group of the Mtra. Celia Dolores Ramírez Rioja, to
each of our editors, designers, editors, who each month
contribute to the preparation of this document.
Sincerely RDM and Multimedia Magazine
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Development and monitoring of RDM Magazine and Multimediato Mtra. Celia
Dolores Ramirez Rioja the whole team of designers, editors, writers and researchers.
that forms RDM Magazine and Multimedia
En relación con todo lo contenido en el sitio, se prohíbe la reproducción, uso, copia, impresión,
distribución, publicación, traducción, adaptación, reordenación y cualquier otro
uso o modificación total o parcial de los datos y obras contenidos en estas páginas, por
cualquier medio y de cualquier forma.
5255-38287797
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Arctic Sea Ice
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Climate change
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Arctic Sea Ice
Climate change is affecting the Arctic more
than any other place on Earth. This region
is warming twice as fast as the rest of the
globe, and one serious consequence is the
loss of significant amounts of sea ice. Sea
ice loss impacts both Arctic ecosystems
and the Earth as a whole. Because Arctic
sea ice is light in color, it reflects most of
the sunlight that hits the sea ice surface
back into space.
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Climate change
Sea ice forms in a fjord in Svalbard. — Credit: Alia
Khan, NSIDC
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Arctic Sea Ice
Because Arctic sea ice is light in color, it reflects
most of the sunlight that hits the sea ice surface
back into space. This prevents too much heat
from being absorbed into the ocean, and helps
to keep the region cool. However, as more sea
ice is lost, more heat is absorbed, which causes
more melting. This amplifies warming, and the
cycle continues. As a result, sea ice is one of
the most rapidly changing areas of the Arctic
environment.
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Climate change
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Earth’s climate
Sea ice plays a critical role in regulating Earth’s
climate, and it influences global weather patterns
and ocean circulations. NSIDC’s Arctic
Sea Ice News & Analysis (ASINA) project, funded
by NASA, provides near real-time data and
monthly insights and analyses on how Arctic
sea ice is changing and what conditions may be
playing a role in ice behavior.
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Climate change
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Climate change
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NASA
NASA has collected passive microwave
data via instruments on satellites continuously
since 1978, and these data are
publicly available through the NASA
NSIDC Distributed Active Archive Center
(DAAC). Instruments continue to circle
the Earth today, providing near realtime
data for scientists studying the
cryosphere and climate.
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The ASINA
project
The ASINA project scientists interpret these data,
making the information that they hold about
sea ice more accessible to other researchers
and the general public. Our analyses focus primarily
on sea ice extent, which is a measurement
of the area of ocean where there is at
least some sea ice. The annual minimum sea
ice extent in September and the annual sea ice
maximum extent in March, when compared with
previous years and decadal averages, are important
indicators of how much ice is being lost
over time.
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Climate change
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The Arctic
sea ice
In April 2012, NSIDC updated its method of calculating
daily values for the Arctic sea ice extent minimum
from a 5-day centered average to a 5-day trailing
average. The new calculations show, for example,
that the record minimum occurred on September
18, 2007, which was two days later than we originally
reported (September 16). In addition, NSIDC
updates extent values, calculated initially with nearreal-time
data, when final processed data becomes
available. These final data, processed at NASA
Goddard, use higher quality input source data and
include additional quality control measures. The recalculations
show a 2007 record low extent of 4.17
million square kilometers (1.61 million square miles).
Our originally published value was 4.13 million square
kilometers. In the final data, the date of the minimum
may also change for some years.
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Climate change
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Ice-covered
Extent defines a region as “ice-covered” or “not icecovered.”
For each satellite data cell, the cell is
said to either have ice or to have no ice, based
on a threshold. The most common threshold
(and the one NSIDC uses) is 15 percent,
meaning that if the data cell has greater than 15
percent ice concentration, the cell is considered
ice covered; less than that and it is said to be
ice free. Example: Let’s say you have three 25
kilometer (km) x 25 km (16 miles x 16 miles)
grid cells covered by 16% ice, 2% ice, and 90%
ice. Two of the three cells would be considered
“ice covered,” or 100% ice. Multiply the grid cell
area by 100% sea ice and you would get a total
extent of 1,250 square km (482 square miles).
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Satellite data
Ice-covered
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Arctic Sea Ice
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Area takes the percentages of sea ice within data
cells and adds them up to report how much of
the Arctic is covered by ice; area typically uses
a threshold of 15%. So in the same example,
with three 25 km x 25 km (16 miles x 16 miles)
grid cells of 16% ice, 2% ice, and 90% ice, multiply
the grid cell areas that are over the 15%
threshold by the percent of sea ice in those grid
cells, and add it up. You would have a total area
of 662 square km (255.8 square miles).
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Scientists at
NSIDC
Scientists at NSIDC report extent because they are
cautious about summertime values of ice concentration
and area taken from satellite sensors. To the sensor,
surface melt appears to be open water rather than water
on top of sea ice. So, while reliable for measuring
area most of the year, the microwave sensor is prone
to underestimating the actual ice concentration and
area when the surface is melting. To account for that
potential inaccuracy, NSIDC scientists rely primarily on
extent when analyzing melt-season conditions and reporting
them to the public. That said, analyzing ice
area is still quite valuable. Given the right circumstances,
background knowledge, and scientific information
on current conditions, it can provide an excellent sense
of how much ice there really is “on the ground.”
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Sea Ice
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Sea ice is classified
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Sea ice is
classified
Sea ice is classified by stages of development
that relate to thickness and age. A simple classification
categorizes sea ice into two primary age
groups: first-year or multiyear. However, for some
applications more detailed classification is
used, such as for navigational purposes, where
finer detail on the age and thickness of the sea
ice is needed.
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Sea ice is classified
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Sea ice is
classified
The World Meteorological Organization
(WMO) has defined the following categories:
New ice is a technical term that refers to ice
less than 10 centimeters (3.9 inches) thick.
As the ice thickens, it enters the young ice
stage, defined as ice that is 10 to 30 centimeters
(3.9 to 11.8 inches) thick. Young ice is
sometimes split into two subcategories, based
on color:
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Sea ice is classified
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Gray ice
• Gray ice (10 to 15 centimeters, or 3.9
to 5.9 inches thick)
• Gray-white ice (15 to 30 centimeters,
or 5.9 to 11.8 inches thick)
• First-year ice is thicker than 30 centimeters
(11.8 inches), but has not survived
a summer melt season.
• Multiyear ice is ice that has survived a
summer melt season and is much thicker
than younger ice, typically ranging
from 2 to 4 meters (78.7 to 157.5
inches) thick.
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Sea ice is classified
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How sea ice
Sea ice grows, forms, and melts strictly in salty
ocean water. This sets it apart from other forms
of ice like icebergs, glaciers, and lake ice, which
form from fresh water or snow. Lake ice tends to
freeze as a smooth layer, while sea ice develops
into various shapes because of the constant
turbulence of ocean water.
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Sea ice is classified
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How sea ice forms
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Sea ice forms more slowly than freshwater for two
main reasons. First, the freezing temperature of salt
water is lower than freshwater; ocean temperatures
must reach -1.8°C (28.8°F) to freeze. Secondly, in
contrast to fresh water, the salt in ocean water causes
the density of the water to increase as it nears
the freezing point.
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Sea ice is classified
As a result, salt water sinks away from the surface
before it cools enough to freeze. Generally,
the top 100 to 150 meters (300 to 450 feet) of
water must cool to the freezing point for sea ice
to form. Furthermore, other factors cause sea
ice formation to be a slow process.
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Stages of ice
As the ocean water begins to freeze, small
needle-like ice crystals called frazil form. These
crystals are typically 3 to 4 millimeters (0.12 to
0.16 inches) in diameter. Because salt doesn't
freeze, the crystals expel salt into the water, and
frazil crystals consist of nearly pure fresh water.
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Frazil crystals
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Stages of ice
formation
Sheets of sea ice form when frazil crystals float
to the surface, accumulate and bond together.
Depending upon the climatic conditions, the ice
formation process follows one of two paths.
In calm waters, frazil crystals form smooth, thin
ice, called grease ice for its resemblance to an
oil slick. Grease ice develops into a continuous,
thin sheet of ice called nilas. Initially, the sheet
is very thin and dark (called dark nilas), becoming
lighter as it thickens. Currents or light
winds often push the nilas around so that they
slide over each other, a process known as rafting.
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Frazil crystals , thin
ice, called grease ice
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Stages of ice
formation
As the ice thickens into a more stable
sheet with a smooth bottom surface, frazil
ice production ceases in the relatively
still waters under the ice. Ice continues
growing when crystals grow directly on
the bottom of the ice surface. This bottom
ice growth is called congelation ice.
Congelation ice crystals are long and
vertical because they grow much slower
than frazil ice.
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Congelation ice
crystals
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Stages of ice
formation
In rough ocean waters, the frazil crystals accumulate into
slushy circular disks, called pancakes or pancake ice,
because of their shape. A signature feature of pancake
ice is raised edges or ridges on the perimeter, caused by
ocean waves bumping the pancakes into each other. If
the motion is strong enough, rafting occurs, where thin
sheets of ice slide over one another. If the ice is thick
enough, ridging occurs, where the sea ice bends or fractures
and piles on top of itself, forming ridges on the surface.
Each ridge consists of above-the-surface ice, called
a sail, and below-the-surface pile of ice, called a keel.
Because of the difference in density between the ice and
the water, most of the ice in a ridge is below the surface.
For instance, keels are about nine times thicker than
their corresponding sail. Particularly in the Arctic, ridges
up to 20 meters (66 feet) thick can form when thick ice
deforms.
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Pancake ice
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Stages of ice
formation
Eventually, the pancakes cement together and consolidate
into a coherent ice sheet. This formation process results
in a rough bottom surface of ice with large undulations.
Ice will continue to grow on the bottom via congelation
growth, adding thickness to the ice cover.
Once sea ice forms into sheet ice, it continues to grow
through the winter as first-year ice. When temperatures
increase in spring and summer, the ice begins to melt. If
the ice remains thin over the winter or if the spring and
summer temperatures are high enough, the ice will melt
out completely during the summer. If the ice grows thick
enough during the winter and/or it experiences less extreme
spring and summer conditions, it will thin during the
summer, but it will not melt completely. In this case, it remains
until the following winter, when it grows and thickens
and is classified as multiyear ice.
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Classified as
multiyear ice.
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Multiyear ice
Multiyear ice has distinct properties that distinguish it from
first-year ice, based on processes that occur during the summer
melt. Multiyear ice contains much less brine and more
air pockets than first-year ice because of processes explained
below. Less brine means “stiffer” ice that is more difficult
for icebreakers to navigate and break through.
In fact, multiyear ice often supplies the fresh water needed
for polar expeditions.
First-year and multiyear ice have different electromagnetic
properties that satellite sensors can detect, allowing scientists
to distinguish the two.
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Multiyear ice is more common in the Arctic than in the Antarctic.
This is because ocean currents and atmospheric circulation move
sea ice around Antarctica, causing most of the ice to melt in the
summer as it moves into warmer waters, or as the upper ocean
heats up because open water areas absorb solar heat. Most of the
multiyear ice that does occur in the Antarctic persists because of a
circulating current in the Weddell Sea, on the eastern side of the
Antarctic Peninsula.
These color-coded maps compare sea ice age, the week of March 4,
2000 (left) and the week of March 5, 2023 (right). Oldest sea ice is
white, and youngest sea ice is dark blue. The extent of old, thick sea
ice in the Arctic has declined significantly since the mid-1980s, when
satellite measurements first became available, and even since the
start of the twenty-first century. — Credit: NOAA Climate.gov based on data from NSIDC
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The Arctic Ocean
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There was another substantial drop during 2005 to 2007. In 2005,
most of the first-year ice melted out completely, so there was very little
replenishment of multiyear ice. Then in 2007, the overall ice extent set
a new record low. Again, a pattern of ice motion transported a lot of
multiyear ice across the Arctic Ocean towards Fram Strait. From 2007
to 2023, multiyear ice has bounced up and down over 1- to 3-year cycles,
but remains lower than pre-2005 levels and the overall trend is
downward. Sea ice typically travels across the Arctic with prevailing
winds and ocean currents, and sea ice exits the Arctic Ocean through
Fram Strait.
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Arctic Sea Ice
As ice thins, its speed increases, transporting more ice through the
Strait, which results in more multiyear ice leaving the Arctic Ocean
at an increasing rate. The Beaufort Gyre, a circular current north of
Alaska, used to act as a nursery for young sea ice where it could
persist and thicken over time. Since the start of the twentyfirst
century, substantial amounts of ice has melted in the southern
arm of the gyre, which has decimated the existing multiyear ice and
allowed much less first-year ice to survive and transition to new
multiyear ice.
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Sea ice properties
Salt and sea ice are an ever-evolving duo. The older the sea
ice, the lower its salt concentration. When sea ice forms, it
tends to be very salty because it contains concentrated droplets
called brine that are trapped in pockets between the ice
crystals. As it ages, the brine gets pushed out. Sea ice that is
four or more years older is nearly free of brine.
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Salinity and sea ice
Salinity is a measure of the concentration of dissolved
salts in water. A common way to define salinity values
had been parts per thousand (ppt), or kilograms of salt in
1,000 kilograms of water.
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Sea ice properties
Today, however, salinity is usually described in practical
salinity units (PSU), a more accurate but more complex
definition. Nonetheless, values of salinity in ppt and PSU
are nearly equivalent. The average salinity of the ocean
typically varies from 32 to 37 PSU, but in polar regions, it
may be less than 30 PSU. Sodium chloride (table salt) is
the most abundant of the many salts found in the ocean.
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Salinity and sea ice
Fresh water freezes at 0°C (32°F), but the freezing point of
seawater varies. For every 5 PSU increase in salinity, the
freezing point decreases by 0.28°C (0.5°F); thus, in polar regions
with an ocean salinity of about 32 PSU, the water
begins to freeze at -1.8°C (28.8°F). The Arctic Ocean is generally
fresher than other oceans, somewhere between 30
and 34 PSU, but salinity levels vary by region, and areas
with strong river inflow may have even lower salinity.
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Pushing brine
out of sea ice
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When needle-like ice crystals called frazil form, highly saline
water accumulates into droplets called brine, which are
typically expelled back into the ocean. Salinity of nearsurface
water then rises. Some brine droplets become
trapped in pockets between the ice crystals. These droplets
are saline, whereas the ice around them is not.
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Ice needles called frasil
The brine remains in a liquid state because much cooler
temperatures would be required for it to freeze. At this stage,
the sea ice has a high salt content.
Over time, the brine drains out, leaving air pockets, and the
salinity of the sea ice decreases. Brine can move out of sea
ice in different ways:
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Pushing brine out of
sea ice
Aided by gravity, the brine migrates
downward through holes and channels in
the ice, eventually emptying back into the
ocean.
The ice surrounding the brine compresses
and breaks the brine pockets, allowing
the brine to escape to the ocean.
When the sea ice begins to melt during
the summer, small freshwater ponds called
melt ponds form on the surface. This
freshwater travels through the cracks and
holes in the ice, washing out remaining
brine.
When the sea ice surface cools, brine increases
in salinity to the point at which it
can melt ice at its underside. This leads to
a downward migration of brine droplets,
ultimately allowing the brine to escape into
the ocean below the ice sheet.
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Melt ponds
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Salt & ocean circulation
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Salt plays an important role in ocean circulation. In
cold, polar regions, changes in salinity affect ocean
density more than changes in temperature. When salt
is ejected into the ocean as sea ice forms, the water's
salinity increases.
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Because salt water is heavier, the density of the water
increases and the water sinks.
The exchange of salt between sea ice and the ocean
influences ocean circulation across hundreds of kilometers.
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Snow on sea ice
Snow typically covers sea ice, insulating
it and delaying melting in the summer.
The snow also modifies the electromagnetic
radiation signal detected by satellites.
Except during a melt season, the
snow is usually dry, wind-blown, and
hard-packed. Wind from a consistent direction
can blow snow into ridges parallel
to the wind direction, just like small
sand dunes. These complex, fragile
shapes are called sastrugi.
If snow cover is thick, especially over relatively
thin sea ice, the weight of the
snow can push the ice down into the
water below. The salty ocean water
floods the snow and creates a salty,
slushy layer. This flooded sea ice is more
common in the Antarctic than the Arctic
because there is typically thinner ice
and more snowfall in Antarctica.
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Sastrugi
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Snow on sea
During summer, as the snow on top of sea ice melts,
the meltwater can accumulate in depressions on the
sea ice surface called melt ponds. These ponds absorb
more heat than the surrounding sea ice from sunlight,
and they grow in area and depth. The fresh water in
melt ponds appears blue because light reflects and
scatters off the sea ice surface from the bottoms and
sides of the melt pond. If a pond melts through the entire
thickness of the ice, the pond's color turns dark, like
the ocean. Melt ponds are more common in the Arctic
than in the Antarctic partly because Arctic ice lasts
longer, giving melt ponds more opportunities to form,
and because Arctic sea ice more often has an uneven
surface, giving melt ponds places to form.
Other features that form on the surface of sea ice are
frost flowers, crystals of ice deposited on the sea ice
when water vapor bypasses the liquid phase and becomes
a solid. Frost flowers roughen the surface and
dramatically alter its electromagnetic signal.
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Melt ponds
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Sea ice & albedo
This graphic shows the difference
in albedo for sea ice, snow, and
the surrounding ocean in the Arctic.
Sea ice reflects between 50
and 70 percent of solar energy,
compared to only 6 percent for the
surrounding ocean.
— Credit: NASA/NSIDC
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Sea ice & albedo
Albedo is a non-dimensional, unitless quantity that indicates
how well a surface reflects solar energy. Albedo
(ranging from -1 to +1) varies between 0 and 1. Albedo
commonly refers to the “whiteness” of a surface, with 0
meaning black and 1 meaning white. A value of 0
means the surface is a “perfect absorber” that absorbs
all incoming energy. Absorbed solar energy can be
used to heat the surface or, when sea ice is present,
melt the surface. A value of 1 means the surface is a
“perfect reflector” that reflects all incoming energy.
Albedo generally applies to visible light, although it
may involve some of the infrared region of the electromagnetic
spectrum. People understand the concept of
low albedo intuitively when they avoid walking barefoot
on blacktop on a hot summer day. Blacktop has a
much lower albedo than concrete, and the black surface
absorbs more of the sun’s energy and reflects less
energy than the lighter concrete.
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Sea ice & albedo
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Sea ice & albedo
Sea ice has a much higher albedo compared to
many other Earth surfaces, particularly the surrounding
ocean. A typical ocean albedo is approximately
0.06, while bare sea ice varies from
approximately 0.5 to 0.7. This means that the
ocean reflects only 6 percent of the incoming solar
radiation and absorbs the rest, while sea ice
reflects 50 to 70 percent of the incoming energy.
The sea ice absorbs less solar energy and keeps
the surface cooler.
Snow has an even higher albedo than sea ice, so
thick sea ice covered with snow reflects as
much as 90 percent of the incoming solar radiation.
This serves to insulate the sea ice, maintaining
cold temperatures and delaying ice melt in
the summer. After the snow does begin to melt,
and because shallow melt ponds have an albedo
of approximately 0.4 to 0.5, the surface albedo
drops to about 0.75. Albedo drops further as
melt ponds grow and deepen.
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Sea ice
formations
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Sea ice is not a continuous, uniformly
smooth sheet of ice, but rather a complex
surface that varies dramatically across even
short distances. Most sea ice features occur
when sea ice either converges or spreads
out.
The bulging sea ice in the foreground is a
pressure ridge, which forms when separate
ice floes collide and stack on top of each other.
— Credit: Michael Studinger, Goddard
Space Flight Center, NASA
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Ice floes and ridges
When wind, ocean currents, and other forces push sea ice
around, ice floes (sheets of ice floating in the water) collide with
each other, and ice piles into ridges and keels. Ridges are small
“mountain ranges” that form on top of the ice; keels are the corresponding
features on the underside of the ice. The total thickness
of the ridges and keels can be several meters (in some cases,
20 meters, or 60 feet, thick), and the surface ridges can
easily be 2 meters (6 feet) or higher.
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Smooth, rolling hills.
Ridges create significant obstacles to anyone trying to traverse
the ice. Ridges are initially blocky with very sharp edges. Over
time, especially during the summer melt, the ridges erode into
smaller, smoother “hills” of ice called hummocks. This process is
similar to the erosion of jagged mountain peaks into smooth, rolling
hills, but at an accelerated pace. When keels erode into
smooth features, they are called bummocks.
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The conductors
The conductors are narrow, linear cracks in the ice that form when
ice floes diverge or shear as they move parallel to each other. The
formation of the conductors is similar to mid-ocean ridges or shear
zones that form from Earth's moving tectonic plates. The width of
conductors varies from a couple of meters to over a kilometer. The
conductors can often branch or intersect, creating a complex network
of linear features in the ice. In the winter, conductors begin to
freeze almost immediately from the cold air.
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The conductors are important for several reasons. First,
seasonal changes influence local and regional climate.
The conductors are much darker than surrounding ice,
which during the summer, results in relatively lower albedo,
or the ability to reflect light. Because of lower reflectivity,
conductors absorb more solar energy than the surrounding
ocean, which heats the water in the conductors
and speeds up the melting of surrounding ice.
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The conductors
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At the beginning of winter, as sea ice begins to refreeze in leads,
brine adds salt to the open ocean layer. In leads that persist
throughout the winter, relatively warm ocean water is exposed to
the cold atmosphere, releasing heat and moisture into the atmosphere.
Thus, Conductors are often accompanied by low-level
clouds downwind. The Conductors are also important for wildlife.
Seals, whales, penguins, and other animals rely on Conductors
for access to oxygen.
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Polar bears in the Arctic often hunt near conductors because they
know that their prey is likely to come to the surface to breathe in
such areas.
Finally, The Conductors are important for navigation. Even when
they freeze, the Conductors tend to contain thinner and weaker ice
that allows submarines to more easily surface through the ice and
icebreakers to more easily traverse the ice.
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Polynyas
Polynyas are areas of persistent open
water where we would expect to find
sea ice. For the most part, they tend
to be roughly oval or circular in shape,
but they can be irregularly shaped,
too. The water remains open because
of processes that prevent sea ice from
forming or that quickly move sea ice
out of the region. There are two types
of polynyas—open-ocean or coastal
polynyas—differentiated by the mechanism
of ice removal. One process
often dominates in a given polynya,
but both can occur.
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Sensible-heat (openocean)
polynyas
Sensible-heat (open-ocean) polynyas. Sensible-heat transfer
occurs between two bodies at different temperatures that
are in contact with each other. The body with the higher
temperature transports sensible heat to the body with the lower
temperature. A sensible-heat polynya forms when water
that is above freezing upwells, or moves from the lower
depths of the ocean to the surface.
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Heat transfers from the warmer water to the ice, melting
it, and preventing new ice from forming. The topography
of the ocean bottom or overturning of water causes the
warm water to rise to the surface. In this type of polynya,
sensible heat from the ocean provides the source of heat
needed to melt the ice. Sensible-heat polynyas usually
form in mid-ocean areas, far from coasts or other barriers.
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Latent-heat (coastal)
polynyas
Latent-heat transfer occurs when matter changes
state; latent heat is absorbed when ice melts,
and it is released into the surroundings when liquid
water freezes. The process is called “latent”
because it is not associated with a change in
temperature, but rather with a change of state.
A latent-heat polynya is characterized by ocean
water at the freezing point. It forms as a result of
winds blowing in a persistent direction that push
the ice away from a barrier, such as the coast,
fast ice (ice that is anchored to the shore or
ocean bottom), a grounded iceberg or an ice
shelf. As new ice grows within polynyas, wind
blows it to the leeward side, while the windward
side remains ice-free. Latent heat is released as
water freezes and also as water evaporates into
the air above the open water. Some sensibleheat
exchange also occurs within latent-heat
polynyas because the water in the polynya is generally
warmer than the air above it, even though
the water is at freezing temperature.
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Latent-heat (coastal)
polynyas
When sea ice forms in polynyas or elsewhere, salt is expelled
into the water, raising the salinity of the nearsurface
water. The salt increases the density of the surface
water, making the surface water heavier than the
water below, causing it to sink.
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In some cases, the high-density surface water mixes
with other masses and sinks all the way to the ocean
bottom. Latent-heat polynyas, particularly those in the
coastal regions of Antarctica, are a major source of the
world's bottom waters, which influence the process of
thermohaline circulation.
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How sea ice changes
Processes that affect the growth and melt of sea
ice are referred to as thermodynamics. In the simplest
sense, when the temperature of the ocean
reaches the freezing point for salt water at -1.8°
C (28.8°F), ice begins to grow. When the temperature
rises above the freezing point, ice begins to
melt.
Because of the ocean’s dynamic nature, sea ice
does not generally grow and melt in a single place.
Instead, most sea ice is constantly moving and
changing location. Only in places near the coast,
where ice can attach to the coast or shallow shelf
region, is it pinned in place and does not move.
Such ice is called fast ice because it is fastened to
the coast.
The amount and rates of growth and melt depend
on the way heat is exchanged within the sea ice, as
well as between the top and bottom of the ice.
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How sea ice thickens
When cold air cools the ocean surface to the freezing
point, sea ice begins to form. As the ocean temperature
nears the freezing point, the water density increases
and the water sinks. Warmer water that replaces it
must also be cooled, so more than just the ocean surface
needs to reach the freezing point. Once ice
begins to grow, it acts as an insulator between the
ocean and atmosphere. Heat from the ocean must be
conducted, or pass through, the sea ice before being
emitted to the atmosphere. Ice growth slows as the ice
thickens because it takes longer for the water below
the ice to lose its heat through ice to reach the freezing
point.
The relationship between thermodynamics and sea ice
thickness can be thought of most simply in terms
of freezing degree days (FDD), which is essentially a
measure of how cold it has been for how long.
The cumulative FDD is simply the daily degrees below
freezing summed over the total number of days the
temperature was below freezing.
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How sea ice thickens
90
The freezing temperature of ocean (saline) water is
typically -1.8°C (28.7°F). If the average daily temperature
was -5.8°C (21.6°F), this would be -4°C (24.8°F) for
one day, as the following equation shows:
(-1.8) — (-5.8) = 4 degrees below freezing
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4 degrees below freezing, Day 1 = 4 cumulative FDD
7 degrees below freezing, Day 2 = 11 cumulative FDD
2 degrees above freezing, Day 3 = 9 cumulative FDD
Scientists have developed different formulas to estimate ice thickness
from thermodynamic growth, using the FDD. One such
formula (from Lebedev 1938) is:
Thickness (cm) = 1.33 * FDD (°C) 0.58
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How sea ice thickens
92
The ice thickness increases at a rate roughly proportional
to the square root of the cumulative FDD. Formulas
such as this are empirical, meaning they are calculated
only with observed data, so they really are simplifications
of the ice growth processes. The formulas assume
that the ice growth occurs in calm water and is
reasonably consistent, and they do not take into account
sea ice motion, snow cover, and other surface
conditions.
Snow cover is one factor that dramatically alters the actual
sea ice thickness calculated from the above formula.
Snow is an effective insulator, slowing the transfer of
heat from the ocean, through the ice, and to the atmosphere.
Snow essentially slows the growth of ice.
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About Ice
Sheets Today
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The Antarctic and
Greenland Ice
Together, the Antarctic and Greenland Ice
Sheets contain more than 99 percent of freshwater
ice on Earth. If they both completely melted,
they would raise sea level by an estimated
67.4 meters (223 feet). Long-term satellite data
indicate that through most of the twentieth century,
the ice sheets made very little contribution
to sea level, and were nearly in balance in annual
snowfall gain and ice or meltwater loss.
However, the stability of the ice sheets has
changed considerably in the twenty-first century.
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Greenland Ice
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Ice Sheets Today offers the latest satellite data
and scientific analyses on surface melting of the
Greenland Ice Sheet in the Northern Hemisphere
and Antarctic Ice Sheet in the Southern Hemisphere.
Surface melt on each ice sheet results
from a combination of daily weather conditions
and the amount of solar energy absorbed
by its snow and ice. Air temperatures, pressures,
and winds drive weather conditions. The
quality of snow, its grain size and color, also influence
melt. Soot, wildfire ash, and other surface
dust darken the snow’s surface and increase
solar energy absorption.
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Greenland Ice
The extent and duration of this surface melting
is an indicator of changing climate and other
conditions. It is a major component of the
waning of Earth's ice sheets.
The Greenland Ice Sheet melt season typically
lasts from April 1 to November 1. The Antarctic
Ice Sheet melt season typically lasts from November
1 to April 1.
Ice Sheets Today is produced by NSIDC and
funded by NASA as part of the ASINA program.
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Arctic sea ice: Walking
on sunshine
Following the 2024 maximum sea ice extent on
March 14, Arctic ice extent has declined slowly
such that 2024 March average is the fifteenth
lowest in the passive microwave satellite record.
The atmospheric circulation pattern for March
2024 featured a strong pressure gradient across
Fram Strait, likely promoting strong winds from
the north and therefore strong sea ice export
out of the Arctic. An update on sea ice age reveals
continued scarcity of the oldest age classes.
A new study highlights the uncertainty as to
when a seasonally ice-free Arctic Ocean can be
expected.
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Arctic sea ice
The average ice extent for March 2024 is 14.87
million square kilometers (5.74 million square
miles), fifteenth lowest in the passive microwave
satellite record. As of the beginning of April
2024, Arctic sea ice extent had dropped by
about 278,000 square kilometers (107,000
square miles) below the March 14 maximum.
Extent is notably low only in the Sea of Okhotsk,
Barents Sea, Labrador Sea, and Davis Strait.
Extent is near average in the Bering Sea, counter
to the pattern of below average extent in this
region characterizing many recent years.
Arctic sea ice extent for March 2024 was 14.87 million square kilometers
(5.74 million square miles). The magenta line shows
the 1981 to 2010 average extent for that month. Sea Ice Index
data. About the data
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Arctic sea ice
The graph above shows Arctic sea ice extent as
of April 2, 2024, along with daily ice extent data
for four previous years and the record low year.
2023 to 2024 is shown in blue, 2022 to 2023 in
green, 2021 to 2022 in orange, 2020 to 2021 in
brown, 2019 to 2020 in magenta, and 2011 to
2012 in dashed brown. The 1981 to 2010 median
is in dark gray. The gray areas around the
median line show the interquartile and interdecile
ranges of the data. Sea Ice Index data.
Credit: National Snow and Ice Data Center
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Arctic sea ice
Air temperatures for March 2024 at the 925 hPa level
(about 2,500 feet above the surface) were below average
in the Barents Sea and along the Eurasian coast at 1 to 3
degrees Celsius (2 to 5 degrees Fahrenheit) contrasting
with above average values of 2 to 5 degrees Celsius (4 to
9 degrees Fahrenheit) over the Canadian Arctic Archipelago,
Greenland, and Baffin Bay . This was attended by
an unusual atmospheric circulation pattern at sea level,
with high pressure over the North American side of the Arctic
and low pressure centered over the Kara Sea,
leading to a strong intervening pressure gradient across
the Fram Strait. This implies strong winds from the north
directed down the strait, which likely favored a strong export
of sea ice out of the Arctic Ocean. Whether this pattern
continues to persist bears watching.
This plot shows the departure from average air temperature
in the Arctic at the 925 hPa level, in degrees Celsius,
for March 2024. Yellows and reds indicate above average
temperatures; blues and purples indicate below average
temperatures.
Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences
Laboratory
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Arctic sea ice
This plot shows average sea level pressure in
the Arctic in millibars for March 2024. Yellows
and reds indicate high air pressure; blues and
purples indicate low pressure.
Credit: NSIDC courtesy NOAA Earth System
Research Laboratory Physical Sciences Laboratory
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Arctic sea ice
Including 2024, the downward linear trend in
March sea ice extent is 37,000 square kilometers
(14,000 square miles) per year, or 2.4 percent
per decade relative to the 1981 to 2010
average. Since 1979, Arctic sea ice loss in
March is 1.68 million square kilometers
(649,000 square miles), which is roughly equivalent
to the size of the state of Alaska or the
country of Iran.
Monthly March ice extent for 1979 to 2024
shows a decline of 2.4 percent per decade.
Credit: National Snow and Ice Data Center
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Arctic sea ice
With the passage of the seasonal maximum sea
ice extent, it is appropriate to provide an updated
assessment of sea ice age. Older, multiyear
ice (ice that has survived at least one melt
season) is generally thicker and more resistant
to melting completely during the upcoming melt
season than first-year ice, which represents ice
growth of the previous autumn and winter. As
seen in the figure, first-year ice dominates, as it
has for the past several years. The extent of
multiyear ice is lower than last year, mostly because
of less second-year ice (one- to two-yearold
ice that has survived two melt seasons), but
it is within the ranges that have been seen since
2008. The oldest ice (greater than four-years
old) has been at very low levels since 2012 and
is slightly lower than last year.
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The top maps show sea ice age for the week of March 11 to March 17
for (a) 1984 and (b) 2024. The bottom graph is a timeseries of the
percent of the sea ice extent within the Arctic Ocean domain (inset
map) for the same time period from 1984 through 2024; color categories
are the same as in the maps. Data and images from NSIDC EA-
SE-Grid Sea Ice Age, Version 4 (Tschudi et al., 2019a) and Quicklook
Arctic Weekly EASE-Grid Sea Ice Age, Version 1.
Credit: Tschudi et al., 2019b
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Loss of Permafrost
Loss of Permafrost.- The melting of the Arctic is becoming
increasingly accentuated, due to the loss of
Permafrost.
The melting of this layer is causing the release of
carbon in the form of CO2 and methane, causing a
critical increase in the greenhouse effect and further
altering the thermal balance of the planet.
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In Siberia alone, massive melting of this layer would
release more than 1,000 gigatons of carbon dioxide
and methane, the main greenhouse gases, Russian
experts warn, Switzerland, Great Britain and Mongolia
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Loss of Permafrost
The aforementioned study also indicates that if carbon
dioxide emissions remain at levels that ensure
that global warming will be less than 1.5°C, summer
sea ice in the Arctic has a real chance of survival. in
the long term (Elcacho, 2016). the inhabitants of the
Arctic.
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On the other hand, the thawing of Permafrost could
bring the growth of forests to the north, creating new
ecosystems, and the potential development of agriculture
in thawed areas, consequently, new business
opportunities for the inhabitants of the Arctic.
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Methane Gas
Methane Gas.- The sediments found on the seabed of the
Arctic have large quantities of methane retained, so the
thaw would generate the release of large columns of methane
into the atmosphere, further increasing global warming
since the greenhouse effect that produced is 23 times
greater than carbon dioxide.
It is estimated that there are 1.5 trillion tons of methane locked
inside the ice-covered Earth, which represents a serious
threat if released into the atmosphere since it is
highly flammable and can form explosive mixtures with air.
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In this regard, in July 2017, two strong methane gas explosions
were recorded in the Yamal Peninsula, northern
Siberia, leaving deep holes at least 50 meters deep. According
to witness statements, the explosions shot fire into
the sky for several minutes and huge chunks of charred
permafrost. In this region of Siberia, more than 700
methane gas release sites have been identified and more
than 12 holes formed since 2014. Dr. Anton Sinitsky, director
of the Arctic Research Center, admitted to being
surprised by the strength of the eruptions and recognized
the risk they present.
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Rise in Sea Level.
Rise in Sea Level.- As has already been indicated,
global warming of the planet is an indisputable fact
mainly due to greenhouse gas emissions, which generates,
among other things, the thermal expansion
of the oceans, the melting of ice. of glaciers and polar
caps, as well as the Arctic and Antarctic.
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According to tide records and satellite measurements,
it is shown that over the last century the average
sea level increased between 10 and 20 centimeters.
However, the annual rate of increase over
the past 20 years has been 3.2 millimeters, roughly
double the average rate of the preceding 80 years.
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Rise in Sea Level.
In August 2015, NASA published a study in which it
shows an alarming increase in sea level of 8 centimeters
in the last 23 years and predicts that by the end of
this century the water could have risen almost a meter.
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Experts from the World Wildlife Fund (WWF) program predicted
that, by the end of the 21st century, global ocean levels will rise
by more than one meter, but forecasts from the international organization
Arctic Monitoring and Assessment Program (AMAP)
are more negative, indicating that ocean levels will rise by 1.6
meters by 2100
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Spread of diseases
Spread of diseases.- As we could see, in the Arctic the
thaws are increasing more and more, generating a
great variation in the microclimates, which causes,
among other things, the increase in the number of insects
that are migrating to other areas, potentially causing
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The spread of existing diseases as well as the emergence
of new pathogens. However, they can not only be
spread in this way, but also by the water that runs as a result
of melting ice, which can transport bacteria from the
corpse of an animal to another living being and become
infected.
In this regard, in the year 1890, there was a large smallpox
epidemic in Siberia, where the city lost more than
40% of its population, the bodies were buried in the permafrost
layer on the banks of the Kolyma River, it is estimated
that, Consequently, the melting of the ice due to
high temperatures could expose them again.
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Natural resources
Natural resources.- According to studies carried
out, it is estimated that in the Arctic there would
be 25% of the oil and gas reserves left on the
planet, as well as reserves of iron, coal, gold and
silver; that in the seas of the Arctic Ocean there
would be more than 62 trillion cubic meters of
gas and more tan 9,000 million tons of oil and on
the shore about 3,500 million tons of oil, these figures
have caused countries such as Denmark
(Greenland), Iceland, Finland, Norway, Sweden,
Russia, Canada and the United States, being
border countries, They are claiming a portion of
the Arctic, becoming an area of conflict as it is
considered a strategic region due to the resources
it has and its geographical position.
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New Maritime Routes
130
New Maritime Routes.- It all started since the legendary
icebreaker Arktika reached the geographic North Pole in
1977, being the first surface ship to do so
(DOMINGUEZ, 2013). The new maritime routes are allowing
the rapprochement between East and West, reducing
this way the costs and operating times. The melting
of the Arctic has allowed accessibility to two new commercial
maritime routes:
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‒ The “Northern Sea Route”.- This route links Europe
with East Asia through the North Sea, transit is mainly
through Russian waters and is known as the “Northern
Sea Route” or NSR. This alternative is 7,000 km shorter
than the traditional route through the Suez Canal, with
savings of time and costs that this entails. Despite their
difficult conditions, there are more and more boats
that pass through it
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El congresista estadounidense republicano Duncan Hunter
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de noviembre
de 2005 un plan
al Senado para reforzar
la barrera fronteri-
za entre los dos países.
La propuesta fue
aprobada el 15 de di-