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Aspects of the Cryosphere. Meto 401 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

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aspects of the cryosphere

Aspects of the Cryosphere

Meto 401

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”

Meto 401

  • 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?

Meto 401

ice station sheba
Ice 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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ice albedo feedback
Ice–Albedo Feedback

July: Variegated darker surface

April: Uniform white surface

Meto 401

evolution of average surface albedo
Evolution of Average Surface Albedo

Gradual seasonal change

+ Abrupt synoptic change

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sheba summary
SHEBA: Summary
  • 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

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movie thawing arctic seaice
Movie: Thawing Arctic SeaIce

Will open the fabled Northwest Passage (summer only)

Meto 401

the two basic climate states nonglacial and glacial polar ice caps
The Two Basic Climate States: Nonglacial and Glacial (Polar Ice 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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descent into our ice epoch
Descent into our Ice Epoch



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our current ice age the last 3m yr
Our 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)

Meto 401

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 increased dramatically since 2004
Our understanding of ice ages has increased 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

Meto 401

current ice age 21k to present
Current Ice Age, 21K to present

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!

Movie: Ice Age Bering Strait

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earth s orbital mechanics
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 shrinkingEarth’s Orbital Mechanics

1. eccentricity —elongation of orbit; 100K-yr period, roughly

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earth s orbital mechanics 2
Earth’s Orbital Mechanics — 2

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.

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movie precession of earth axis
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 elements have periodic behavior
Orbital Elements Have Periodic Behavior

lending hope that ice ages might be predictable!

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earth s orbital mechanics 3
Earth’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 for milankovitch from imbrie paper
The Smoking Gun for Milankovitch (from Imbrie paper)

Fourier spectrum of past 0.5M yr had peaks at exactly the three periods of Earth orbital variation!

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ocean drilling
Ocean 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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temperature last 18k years
Temperature — 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


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backsliding heinrich event
Backsliding: 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 squares
Heinrich Events in History (red 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 coring
Ice Coring

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how did we get co2 and temperature so far back
How did we get CO2 and temperature so far 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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temperature last 100m years
Temperature — 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!

Meto 401

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)

Meto 401

where s the ice
Where’s the Ice?

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.

Meto 401

polar view
Polar 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 climate
Ice 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.

Meto 401

global warming and the cryosphere
Global Warming and the Cryosphere

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.

Meto 401

news on the polar warming front
News 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.

Meto 401

is the arctic feeling amplified warming
Is the Arctic Feeling Amplified Warming?

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.

Meto 401

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.

Meto 401

perennial arctic sea ice cover decreasing 10 decade
Perennial Arctic Sea Ice Cover Decreasing ~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?

Meto 401

wintertime in the antarctic
Wintertime in the Antarctic

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

Meto 401

west antarctic ice sheet grounded below sea level
West Antarctic ice sheet grounded below sea level
  • 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.

Meto 401

diagram of an ice sheet
Diagram of an Ice Sheet

Note depression under ice sheet; “glacial rebound” when melts

Moves more like a sandpile than a mountain glacier.

Meto 401

collapsing larsen ice shelf antarctic peninsula which is 2 of antarctica
Collapsing Larsen Ice Shelf, Antarctic Peninsula (which is 2% of Antarctica)

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.

This 21 Feb 2000 Landsat 7 image shows a portion of the Larsen Ice Shelf and drifting icebergs that have recently calved from it.

Meto 401

larsen b ice shelf collapse
Larsen-B Ice Shelf Collapse

size of Rhode Island

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larsen ice shelf under a microscope
Larsen 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 collapsing
3 West Antarctic Glaciers exhibit signs of collapsing

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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huge icebergs are calving from antarctic ice shelves
Huge icebergs are calving from Antarctic ice shelves

Connecticut-size iceberg calved from Ross Ice Shelf in 2002

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calving glaciers
Calving Glaciers

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.

Meto 401

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 margins are thinning blue rapidly in places
Greenland ice margins are thinning (blue), rapidly in places

Jakobshavns Ice Stream thinned 70 meters in 5 years.

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greenland growth of melt zone 2001 3
Greenland: Growth of Melt Zone, 2001-3

Many more melt ponds in 2003

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collapse of ward hunt ice shelf arctic
Collapse of Ward Hunt Ice Shelf, Arctic

Made world news in 2003

North coast Ellesmere Isl.

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mountain glacier retreat worldwide
Mountain 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.

Meto 401

microwave remote sensing of sea ice
Microwave Remote Sensing of Sea Ice
  • 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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a rare look at the north pole
A Rare Look at the North Pole

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.

Leads continually open and close due to shifting winds and ocean currents.

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n hemisphere monthly average sea ice extent
N. Hemisphere Monthly-Average Sea Ice Extent

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.

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n hemisphere annual average sea ice extent
N. Hemisphere Annual-Average Sea Ice Extent

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.

Meto 401


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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november n american snow cover
November N. American Snow Cover

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

Meto 401

polar research is ideal for satellites
Polar research is ideal for satellites

Remote sensing is a natural solution to the remoteness, harshness and dangers of polar regions

Near-polar orbit configuration produces more frequent polar observations than any other place on Earth

Meto 401

satellites and the cryosphere
Satellites 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.

Meto 401

  • 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 orbit lines antarctica
IceSat Orbit Lines, Antarctica

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 data
Actual IceSAT Data


Meto 401