aspects of the cryosphere meto 401 [email protected]
TRANSCRIPT
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Why study polar regions?Why study polar regions?
• Sea level change from melting
• Repository of paleoclimatic information– Best view of abrupt climate change
• Unequivocal & integrative signals of climate change– Polar amplification– “Canary in the coal mine”
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International Polar Year: 50International Polar Year: 50thth Anniversary Anniversary of International Geophysical Year (IGY)of International Geophysical Year (IGY)
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SHEBASHEBA
• the first extensive sea ice experiment in 30 yr– since AIDJEX, in which I was also involved
• an icebreaker for a year, frozen in the Arctic ice
• best modern instruments
• helicopter, aircraft, under-ice robotic surveys
• I had a tethered balloon there!
• confirmed what U.S. nuclear submarines were seeing: dramatic thinning of pack ice
• Arctic Oscillation?
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SHEBA: ApproachSHEBA: Approach
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Ice Station SHEBAIce Station SHEBA
Year long icebreaker drift 2 Oct 1997: 75 N, 142 W 11 Oct 1998: 80 N, 166 W Total drift ~ 2800 km As crow flies ~ 800 km
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Seasonal Evolution of Pack IceSeasonal Evolution of Pack Ice
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Net mass loss during SHEBA year!Net mass loss during SHEBA year!
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Ice–Albedo FeedbackIce–Albedo Feedback
April: Uniform white surface
July: Variegated darker surface
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Evolution of Average Surface AlbedoEvolution of Average Surface AlbedoGradual seasonal change
+ Abrupt synoptic change
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Albedo evolution: smooth seasonal decrease + discrete synoptic changes
Decrease in average albedo from about 0.9 to 0.4 Spatial variability of albedo increased during melt
Clouds In winter: significant (11 C) warming associated with appearance of clouds. In summer: clouds still had a net warming effect. The blanket beat the umbrella.
In Fall 1997 the ice cover was thinner than expected; much to our surprise it was even thinner in the fall of 1998
SHEBA: SummarySHEBA: Summary
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Movie: Movie: Thawing Arctic SeaIceThawing Arctic SeaIce
Will open the fabled Northwest Passage (summer only)
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The Two Basic Climate States: The Two Basic Climate States: Nonglacial and Glacial (Polar Ice Nonglacial and Glacial (Polar Ice
Caps)Caps)• Continental drift, sealevel change, and CO2 all
contributed to planetary temperature shifts on the million-yr timescale
• Glacial states are marked by multiple expansions of continental ice sheets into midlatitudes.– Fluctuations on time scales of tens of thousands of years
• Fluctuations of ice sheets in last 3M yr correlate with orbitally-induced changes in solar radiation distribution with latitude– terrestrial feedbacks (ice sheet dynamics, ocean
temperatures, CO2) are responsible for a significant modulations of the orbital signal
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We keep We keep bouncing bouncing back from back from
ice ice onslaughtsonslaughts
SnowballEarth?
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Descent into our Ice EpochDescent into our Ice Epoch
SnowballEarth?
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Our Current Ice Age -- the last 3M yrOur Current Ice Age -- the last 3M yr
• Some say it began when the isthmus of Panama closed, cutting off communication between the world oceans and forcing the Gulf Stream to carry vast amounts of warm water northward where it evaporated and helped create the ice sheets
• Previously the northern ocean had been too cold to cause enough snowfall to grow ice sheets
• Antarctica starting glaciating ~10-30M yr ago, and its chilling effect added to the decline
• Main cause of Antarctic glaciation may have been falling CO2 (formerly thought to be opening of Drake Passage by continental drift)
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Within the current 3M-yr ice age...Within the current 3M-yr ice age...
• there have been ~ 8 glacial periods of roughly 90K yr duration, separated by short interglacials of roughly 10K yr duration
• the glacial-interglacial temperature curve is like a sawtooth — slow fall into a glacial, rapid rise out of it (with occasional backslidings)
• before the latest 8 glacials, were ~16 others of different character
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Our understanding of ice ages has Our understanding of ice ages has increased dramatically since 2004increased dramatically since 2004
• … because of the Dome C ice core, which goes back almost 800K yr, or almost 8 glacial cycles
• until then, we only had the Vostok ice core, which went back almost 400K yr
• based on the Vostok core, we should have been sliding back into a glacial period by now (our 10K-yr interglacial should have been over)
• BUT… the Dome C record shows the interglacial most analogous to ours (in terms of Earth’s orbit) last 28K yr, not 10K yr
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Current Ice Age, 21K to presentCurrent Ice Age, 21K to present
Movie: Ice Age Bering Strait
Movie: Ice Age Map
• Asia, Africa, S. America remarkably unglaciated
• N. America got the worst of it, by far• No way to migrate into N. America using
Bering Strait land bridge until ~13K yr ago– some anthropologists say humans were in N.
America 20K yr ago!
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Milankovitch Theory (1920s) states that cyclical variations in three elements of Earth-Sun geometry combine to produce variations in the amount of solar energy that reaches Earth; these variations are enough to start ice sheets growing or shrinking
1. eccentricity —elongation of orbit; 100K-yr period, roughly
Earth’s Orbital MechanicsEarth’s Orbital Mechanics
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2. Obliquity — the angle that Earth's axis makes with the plane of Earth's orbit. 40K yr period, roughly.
3. Precession — the Earth's axis of rotation behaves like the spin axis of a top; it traces a circle on the celestial sphere over a period of time.
Earth’s Orbital MechanicsEarth’s Orbital Mechanics — 2 — 2
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Movie: Precession of Earth axis
• 21000-yr period, roughly
• Moon has kept Earth from tilting too much (there is a theory that Mars, lacking a big moon, tilted as much as 90 deg in the past)
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Orbital Orbital Elements Elements
Have Have Periodic Periodic BehaviorBehavior
lending hope that ice ages
might be predictable!
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Earth’s Orbital Mechanics — 3Earth’s Orbital Mechanics — 3
• Using these three orbital elements, Milankovitch formulated a mathematical model that calculated latitudinal differences in sunlight and the corresponding surface temperature for 600K yr prior to 1800. He then correlated these changes with the growth and retreat of the Earth’s Ice Ages.
• His first monograph on the subject in 1920 was alternately ignored and refuted for about 50 years. Finally, in 1976, a study by Imbrie et al. published in Science examined deep-sea sediment cores over 450,000 yr to seemingly confirm Milankovitch’s theory.
• The theory is still controversial, however, because no climate model has been able to create ice ages using the Milankovitch forcing (the changes of sunlight distribution caused by orbital variations)
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The Smoking Gun The Smoking Gun for Milankovitch for Milankovitch
(from Imbrie (from Imbrie paper)paper)
Fourier spectrum of past 0.5M yr had peaks at exactly the three periods of Earth orbital variation!
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Ocean DrillingOcean Drilling
...has been our main source of information on Ice Age
...confirmed Milankovitch theory of Ice Ages...maybe
Sediments don’t go back as far as you’d think: ocean floor is constantly being recycled and is never older a few hundred million yr.
Shackleton just won big AGU award for showing in 1970s that global ice volume is related to oxygen isotope fraction in dead plankton (the ones with calcareous (CaCO3) shells) that fall to bottom of ocean.
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Ocean Cores to 1978 (over 15000)Ocean Cores to 1978 (over 15000)
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Ocean Core ExampleOcean Core Example
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Temperature — Last 18K yearsTemperature — Last 18K years
• it was only ~5C colder at peak of last glaciation• sudden climate shifts are possible• it wasn’t all warming!• the Sun and CO2 may have controlled this, partly
Note:
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Backsliding: Heinrich EventBacksliding: Heinrich Event
11K yr ago: parade of icebergs from melting N. American ice sheets chills N. Atlantic
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Heinrich Events in History (red Heinrich Events in History (red squares)squares)
plot of Sea Surface Temperature (SST) vs time
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Prof. Ruddiman (U Va) says...Prof. Ruddiman (U Va) says...
• Humans have kept the planet out of the next ice age by doing two things:– deforesting, starting 8K yr ago (releases CO2)– growing rice, starting 5K yr ago (releases CH4)– BUT… this was before the Dome C ice core!
• He also sees the signature of the Black Plague in the temperature record of the Little Ice Age, and ascribes it to the regrowth of forests after farms were massively abandoned -- i.e., human dieback lowered atmospheric CO2 and cooled the planet
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Ice CoringIce Coring
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Vostok Ice Vostok Ice Core: Core:
Temperature, Temperature, CO2, CH4CO2, CH4
(Antarctic)(Antarctic)
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Greenland and Antarctic ice cores Greenland and Antarctic ice cores agreeagree
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How did we get CO2 and temperature so far How did we get CO2 and temperature so far back?back?
CO2 and CH4 trapped in air bubbles; stays same over eons once encased (which may take 100s of yr)
Temperature inferred from oxygen isotopes or deuterium
A heroic endeavor — big technology leap to drill that deep and recover core
Cores stored in giant Denver freezer, mainly
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Ice core drilled at Dome C, Ice core drilled at Dome C, AntarcticaAntarctica
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Ice core drilled Ice core drilled at Dome C, at Dome C,
Antarctica, goes Antarctica, goes back 720K yrback 720K yr
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Deuterium values from Dome C ice core Deuterium values from Dome C ice core show change in nature of interglacials 400K show change in nature of interglacials 400K
yr agoyr ago
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Comparison Comparison of 400K-yr of 400K-yr
ago ago interglacial interglacial (blue) with (blue) with current one current one
(red)(red)
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Temperature — Last 100M yearsTemperature — Last 100M years
• the last 2-3M yr has been the “Ice Age”• there have been perhaps 8 glaciations in the Ice Age• 50M yr ago it was warm even at the poles!
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Why did temperature slide downhill?Why did temperature slide downhill?
• probably CO2 (and maybe CH4) decreasing; they may control temperature on both short (10K yr) and long (10M yr) time scales
• continental drift played some role– recycling C– changing ocean dynamics (Panama closed 4Myr ago)– creating Antarctica
• it happened before:– 250M yr ago– 600M yr ago (Snowball Earth?)– 2.4B yr ago (Sun was 15% less luminous)
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Current ClimateCurrent Climate
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Ice-Covered Areas Deceptively SmallIce-Covered Areas Deceptively Small
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Greenland and Antarctica
contain about 75% of the world’s
fresh water, enough to raise sea
level by over 73 m.
Measurements of ice elevations
have been made by satellite
radar altimeters for parts of the
polar ice sheets.
Now, the IceSAT laser altimeter
will provide more accurate
measurements and not miss the
poles like earlier satellites did.
Where’s the Ice?Where’s the Ice?
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Polar ViewPolar View
Complete opposites:
Arctic is landlocked sea-ice ocean,
Antarctic is sea-locked land ice sheet
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Ice and Snow Strongly Affect ClimateIce and Snow Strongly Affect Climate
• During Northern Hemisphere winter, they
• blanket up to 15% of the Earth’s surface and
• (b) reflect up to 80% of the Sun’s radiant energy back to space.
• During the Southern Hemisphere winter, they cover about half this area.
• But their influence is far larger than their areal coverage would indicate.
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Global warming should decrease Earth’s snow and ice cover,
which in turn would increase the absorption of solar
radiation, amplifying the warming (a positive feedback).
The meltback of sea ice would also increase the ocean heat
flux to the atmosphere, again amplifying the warming. It
would also increase the vapor flux to the atmosphere, which
might enhance clouds. What would that do? We don’t really
know.
Global Climate Models (not all...) have been predicting
amplified warming in the Arctic since Manabe in late 1960’s.
But...the observational data were too sparse to tell.
Global warming should decrease Earth’s snow and ice cover,
which in turn would increase the absorption of solar
radiation, amplifying the warming (a positive feedback).
The meltback of sea ice would also increase the ocean heat
flux to the atmosphere, again amplifying the warming. It
would also increase the vapor flux to the atmosphere, which
might enhance clouds. What would that do? We don’t really
know.
Global Climate Models (not all...) have been predicting
amplified warming in the Arctic since Manabe in late 1960’s.
But...the observational data were too sparse to tell.
Global Warming and the CryosphereGlobal Warming and the Cryosphere
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News on the Polar Warming FrontNews on the Polar Warming Front
a 40% thinning of Arctic sea ice,1950s to 1990s
a 4%/decade reduction in the surface area of sea ice
a 0.6C/decade temperature increase since the 1960s in the high northern latitudes
marked warming trend on Antarctic Peninsula, faster than the planet as a whole. But Antarctica as a whole is not warming…
Some monster Antarctic icebergs have calved recently...but also we are monitoring them better.
Greenland is warming, but has only reached the warmth of the 1930s now.
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Yes. We finally have enough data to see it. Winter temperatures in the northernmost regions of the world have warmed alarmingly in a very short time. Over the 30-yr period shown, average winter temperatures in central Siberia and parts of Alaska warmed by as much as 5–6°C. Alaskan newspapers are filled with warming stories.
Is the Arctic Feeling Is the Arctic Feeling Amplified Warming?Amplified Warming?
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And What about Sea Ice Melting?And What about Sea Ice Melting?
That’s going on too...nuclear submarines saw it, but it was a Cold War secret!Declassified in mid-90s.
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Perennial sea ice Perennial sea ice has been pulling has been pulling
back from Alaskan back from Alaskan side of Arctic Oceanside of Arctic Ocean
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Perennial Arctic Sea Ice Cover Decreasing Perennial Arctic Sea Ice Cover Decreasing ~10%/decade~10%/decade
• Ice-albedo feedback is positive (i.e., destabilizing)
• 37% of 2*CO2 warming caused by sea ice-albedo feedback (Parkinson/Rind using GISS model)
• NO perennial (summer) Arctic ice cover by 2050?
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SSMI sea ice data for
Sept 1999 and
QuikScat land ice
information for July
1999. White over
oceans = waters 95%
or more covered by
ice. The gray scale
over the Antarctic ice
sheet differentiates
different kinds of ice.
Image credit: C. Parkinson, N. DiGirolamo, D. Cavalieri, for sea ice; Tim Liu for land ice
Wintertime in the AntarcticWintertime in the Antarctic
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West Antarctic ice sheet grounded below sea West Antarctic ice sheet grounded below sea levellevel
• grounded on marine sediment experiencing high geothermal heat flow
• Inherently unstable? We don’t know. There isn’t any evidence of collapse in the fossil record.
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The W. Antarctic ice sheet is The W. Antarctic ice sheet is complicatedcomplicated
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Projection of the effect of complete West Projection of the effect of complete West Antarctic melting on FloridaAntarctic melting on Florida
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Diagram of an Ice SheetDiagram of an Ice Sheet
Note depression under ice sheet; “glacial rebound” when melts
Moves more like a sandpile than a mountain glacier.
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Ice Sheet DiagramIce Sheet Diagram
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On the northermost thumb of Antarctica, warming surface temperatures splintered an ice shelf by an unexpected mechanism. Landsat 7 detected melt ponds on the surface of the Larsen Ice Shelf and a sophisticated ice-shelf computer model showed that added pressure from surface water filling crevasses, then freezing, can crack the ice entirely through. Will become more widespread if Antarctic Peninsula summer temperatures continue to rise.
Collapsing Larsen Ice Shelf, Antarctic Peninsula Collapsing Larsen Ice Shelf, Antarctic Peninsula (which is 2% of Antarctica)(which is 2% of Antarctica)
This 21 Feb 2000 Landsat 7 image shows
a portion of the Larsen Ice Shelf and
drifting icebergs that have recently
calved from it.
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Larsen-B Ice Shelf CollapseLarsen-B Ice Shelf Collapse
size of Rhode Island
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Larsen Ice Shelf Under a MicroscopeLarsen Ice Shelf Under a Microscope
The upper image is an overview of the shelf’s edge, while the lower image is displayed at Landsat resolution of 30 m.
The labeled melt pond in the lower image measures ~ 1.6x1.6 km.
Biggest effect in the Antarctic Peninsula (where temperatures have increased 2.5oC in 50 years). 2000 km2 of Larsen Ice Shelf disintegrated in 2 days.
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3 West Antarctic Glaciers exhibit signs of 3 West Antarctic Glaciers exhibit signs of collapsingcollapsing
Thinning increasing towards coast (satellite altimetry)
Flow acceleration (InSAR)
Retreat of grounding line (Landsat)
Calving of large icebergs (MODIS)
All observations by satellite sensors. Most of this area has never been visited by humans.
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More More evidence…evidence…
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Huge icebergs are calving from Antarctic ice Huge icebergs are calving from Antarctic ice shelvesshelves
Connecticut-size iceberg calved from Ross Ice Shelf in 2002
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At left: MODIS image shows the Ross Ice Shelf near Roosevelt Island, Antarctica, in Mar 2000, prior to calving of iceberg B-15. Large iceberg calving events only occur every few years, but their frequency appears to be increasing.
At right: B-15 in the process of breaking away from the ice shelf in Mar 2000. B-15 is one of the largest icebergs ever observed (300x40 km), about 2x the size of Delaware. The iceberg formed along cracks in glacier ice moving off the Antarctic continent.
Calving GlaciersCalving Glaciers
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A Greenland GlacierA Greenland Glacier
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So..What’s Going on with Greenland?So..What’s Going on with Greenland?
The margins are thinning in some places by 1 m/yr. A conservative estimate indicates a net loss of ~ 51 km3/yr of ice from the entire ice sheet, sufficient to raise global sea level by 0.005 in/yr, or approximately 7% of the observed rise. The thinning cannot be accounted for by increased melting alone; it appears that ice must be flowing more quickly into the sea through glaciers.
Aircraft survey from NASA Wallops
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Greenland ice Greenland ice margins are margins are
thinning thinning (blue), rapidly (blue), rapidly
in placesin places
Jakobshavns Ice Stream thinned 70 meters in 5 years.
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Greenland: Greenland: Growth of Growth of Melt Zone, Melt Zone,
2001-32001-3
Many more melt ponds in 2003
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Collapse of Ward Hunt Ice Shelf, Collapse of Ward Hunt Ice Shelf, ArcticArctic
Made world news in 2003
North coast Ellesmere Isl.
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Mountain Glacier Retreat WorldwideMountain Glacier Retreat Worldwide
Muir Glacier near Juneau in SE Alaska retreated more than 7 km from 1973 to 1986. By 1986, Burroughs Glacier (A), cut off from its source of ice, was collapsing into a melting ice field.
1973 1986
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Microwave Remote Sensing of Sea Microwave Remote Sensing of Sea IceIce
• Discovered by accident in 1972 — ESMR (Electrically Scanning Microwave Radiometer) could see– ocean has low emission of thermal IR radiation– sea ice has high emission– multi-year sea ice has different emission than first-year
ice
• These differences are caused mainly by sea salt
• Salty water is reflective in the microwave, like a metal (both have a lot of free electrons); – emissivity + reflectivity = 1 by Kirchhoff’s Law, so a
good reflector is a poor emitter
• Sea ice rejects brine when it forms (you can drink melted old ice) hence is much less reflective in microwave
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Microwave Remote Sensing, Sea IceMicrowave Remote Sensing, Sea Ice
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TheTheHeartbeat Heartbeat of Arcticof ArcticSea IceSea Ice
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Full-Year Sea Ice Movies (1999)Full-Year Sea Ice Movies (1999)
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Microwave-Retrieved Sea Ice AmountMicrowave-Retrieved Sea Ice Amount
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The area is usually shrouded in clouds but on 5 May 2000, MODIS captured this true-color image. The dark irregular lines are cracks or “leads” in the sea ice.
A Rare Look at the North PoleA Rare Look at the North Pole
Leads continually open and close due to shifting winds and ocean currents.
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Note large seasonal cycle: min ~ 7M km2 in late summer to max ~ 15M km2 in late winter. Year-to-year differences SEEM small.
Data from Scanning Multichannel Microwave Radiometer on NASA’s Nimbus 7 satellite and from Special Sensor Microwave Imagers on Defense Meteorological Satellites.Plot : Claire Parkinson, et al., J. Geophys. Res., 1999.
N. Hemisphere Monthly-Average Sea Ice ExtentN. Hemisphere Monthly-Average Sea Ice Extent
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Annual-averaging reveals trend (albeit with large excursions) not visible in monthly-average plot. Trend line has downward slope of 34,000 km2/yr. Recent findings by Comiso are even more surprising, indicating loss of summer ice by 2050.
N. Hemisphere Annual-Average Sea Ice ExtentN. Hemisphere Annual-Average Sea Ice Extent
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PermafrostPermafrost
Frozen ground, saturated with ice
Underlies ~25% of the land mass of N. Hemisphere
Can be 100s of meters thick
The “permafrost line” has been moving north
Meas’ts at 125 m show 2-4 C warming over past 100 yr
Permafrost in Siberia stores vast amounts of CH4; its release would enhance greenhouse warming
Network is being developed
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Snow from MODISSnow from MODIS
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Red line = 35-year average Nov snowline.Light gray = covered by clouds for entire period. Gray = no data.
Seasonal snow cover is vital to the water resources of many parts of the world, notably India and the U.S. West.
data from MODIS
November 1-7, 2000
November 16-23, 2000
November N. American Snow CoverNovember N. American Snow Cover
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Polar research is ideal for satellitesPolar research is ideal for satellites
Near-polar orbit configuration produces more frequent polar observations than any other place on Earth
Remote sensing is a natural solution to the remoteness,
harshness and dangers of polar regions
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Satellites and the CryosphereSatellites and the Cryosphere
• Satellite data provide one of the best ways to observe snow and ice coverage and variability.
• Visible and infrared sensors provide high-resolution images under sunlit, cloud-free conditions, ...
• while microwave sensors provide coarse-resolution observations under ANY conditions — dark or light, cloudy or cloud-free.
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NASA’s Newest — IceSat (a big laser)NASA’s Newest — IceSat (a big laser)
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ICESatICESat
• First cryospheric satellite mission ever
• Addresses fundamental climate questions:– Ice sheet mass balance– Ice sheet behavior– Polar stratospheric clouds – Clouds and aerosols
• Further uses being developed for:– Sea ice thickness– Snowfall gauge
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IceSat Shooting StrategyIceSat Shooting Strategy
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IceSat Orbit IceSat Orbit Lines, Lines,
AntarcticaAntarctica
8-day repeat cycle
only goes to 86° S
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IceSAT will see clouds too...IceSAT will see clouds too...
a complicating factor for the ice people but a boon for the cloud people
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Actual IceSAT DataActual IceSAT Data
Antarctica