Chapter 4. Observations: Changes in Snow, Ice and Frozen Ground

Jon DemuthPhil TivelChad Blevins

Background

• Cryosphere– Consists of: snow, river and lake ice, sea ice

glaciers and ice caps, ice shelves and ice sheets, frozen ground

– 2nd largest component of the climate system– Linked to energy budget– Natural sensor of climate variability– important climate change variable

Chapter Summary

• Snow decrease• Later formation of lake/river ice• Earlier melt of lake/river ice• Sea ice extent decrease• Loss of Glacier and Ice Caps• Sea level rise• Permafrost loss

Snow cover in NH dropped 5 %, in SH records indicate decrease or no changes (1966-2005)

Northern Hemisphere snow-covered area anomalies: This shows Northern Hemisphere snow-covered area departures from monthly means, 1978-2005, from NOAA snow charts (orange) and microwave satellite (purple/green) data sets. The NOAA time series for this period exhibits a significant decreasing trend of -2.0 percent per decade (solid orange line); the microwave snow cover time series exhibits a decreasing trend of -0.7 percent per decade that is not significant at a 90 percent level (dashed green line).

The National Snow and Ice Data Center Supporting Cryospheric Research Since 1976449 UCB University of Colorado Boulder, CO 80309-0449

Satellite data show continuing decline in mean arctic sea ice extent since 1978

Extent comparisons: This graph compares 5-day running means for Arctic sea ice extent (area of ocean with ice concentration of at least 15 percent) for the long-term mean (1979-2000), the previous record low (2005) and the record low (2007). Although the summer of 2007 began with slightly greater ice extent than in 2005, rapid melting commenced in late June. During a two-week period in late June and early July 2007, sea ice declined by an area roughly equal to the size of Kansas each day. Sea ice extent continued its steady decline through mid-September, 2007. Image provided by National Snow and Ice Data Center, University of Colorado, Boulder.

The National Snow and Ice Data Center Supporting Cryospheric Research Since 1976449 UCB University of Colorado Boulder, CO 80309-0449

The National Snow and Ice Data Center Supporting Cryospheric Research Since 1976449 UCB University of Colorado Boulder, CO 80309-0449

Northwest Passage: The maroon line marks the route of the Northwest Passage that opened up in 2007.

The National Snow and Ice Data Center Supporting Cryospheric Research Since 1976449 UCB University of Colorado Boulder, CO 80309-0449

http://www.nasa.gov/centers/goddard/mpg/143497main_sea_ice2005_composite_320x240.mpg

Mass loss of glaciers and ice caps

Glacier mass balance: Image courtesy of Mark Dyurgerov, Institute of Arctic and Alpine Research, University of Colorado, Boulder. The National Snow and Ice Data Center

Supporting Cryospheric Research Since 1976449 UCB University of Colorado Boulder, CO 80309-0449

1941-2004 comparison: Glacier Bay National Park and Reserve's White Thunder Ridge as seen on August 13, 1941 (left) and August 31, 2004 (right). Muir Glacier has retreated out of the field of view, Riggs Glacier has thinned and retreated significantly, and dense new vegetation has appeared. Muir Glacier was more than 2,000 feet thick in 1941. 2004 USGS photo by B. F. Molnia; 1941 photo by W. O. Field. See the Repeat Photography of Glaciers Special Collection in the Glacier Photograph Collection to access this and other photograph pairs.

1928-2000 comparison: These photos of the South Cascade Glacier in the Washington Cascade Mountains show dramatic retreat between 1928 and 2000. Photos courtesy of the USGS.

The National Snow and Ice Data Center Supporting Cryospheric Research Since 1976449 UCB University of Colorado Boulder, CO 80309-0449

Sea level rise contributors: Comparison of volume (white), area (grey) and percent contribution to sea level rise (red) by small glaciers and ice caps, and the Greenland and Antarctic Ice Sheets.

Small glacier/ice cap contribution: The cumulative contribution to sea level from small glaciers and ice caps (red) plotted with the annual global surface air temperature anomaly (blue) .

Ice sheets have very likely contributed to sea level rise

The National Snow and Ice Data Center Supporting Cryospheric Research Since 1976449 UCB University of Colorado Boulder, CO 80309-0449

Permafrost temperature has increased

Coastal erosion: Intact permafrost is extremely strong and resistant to erosion, and intact sea ice minimizes wave action in the ocean. When sea ice retreats and permafrost degrades, coastlines become much more vulnerable to erosion. These pictures were taken in Shishmaref, Alaska, during a storm in 2003. Only two hours separate the first photo from the second. For reference, red arrows mark the barrel. By the time the second photograph was taken, the coastline in the foreground had retreated past the barrel. Although coastal erosion was significant, this was not a particularly strong storm.

Maximum extent of frozen ground has decreased The National Snow and Ice Data Center Supporting Cryospheric Research Since 1976449 UCB University of Colorado Boulder, CO 80309-0449

4.1 IntroductionPhysical Properties: -surface reflectivity and latent heat -presence or absence of snow or ice

Cryosphere on land = 75% of worlds freshwater (7m and 57m rise)

Currently Ice covers 10% of land and 7% of oceans

All parts contribute to short term climate

Changes in glaciers and ice caps reflect climate variations

Permafrost accounts for 24% of land in NH

4.2 Changes in Snow Cover• High albedo of snow very important on surface energy

– Decreasing because of soot• Snow cover data collected since 1966 – longest env. Data set of any kind

• SCA has declined in spring and summer but not a lot in winter– Spring melt 2 weeks early– Significant decline in mean SCA

• temp variations play significant role in trends of SCA• N. America SCA increased in Nov, Dec and Jan (1915-2004)• Eurasia SCA in mountains show recent decline and lower elevations• S. America show great interannual variablitly but little or no long –

term trend• S. East Australia significant snow depth declines

4.2 Changes in Snow Cover

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4.2 Changes in Snow Cover

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4.2 Changes in Snow Cover

Frei, A. and G. Gong, 2005. Decadal to Century Scale Trends in North American Snow Extent in Coupled Atmosphere-Ocean General Circulation Models. Geophysical Research Letters, 32:L18502, doi: 10.1029/2005GL023394.

Automated Model Discussion:March 24, 2008

Area Covered By Snow: 25.5% Area Covered Last Month: 47.2%Snow Depth Average: 6.0 in Minimum: 0.0 in Maximum: 664.1 in Std. Dev.: 17.4 inSnow Water Equivalent Average: 1.7 in Minimum: 0.0 in Maximum: 296.3 in Std. Dev.: 5.5 in

NOAA: National Operational Hydrologic Remote Sensing Center

NOAA: National Operational Hydrologic Remote Sensing Center

4.3 Changes in River and Lake Ice

Freeze-up and breakup dates for river and lake ice show spatial variability – later and earlier

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4.3 Changes in River Ice

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4.3 Changes in Lake Ice

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Importance of Sea Ice

• Provides Albedo effect• Modifies the exchange of heat, gasses and momentum

between the atmosphere and polar oceans• Redistributes freshwater via the transport and subsequent

melt of relatively fresh sea ice.• Insulates ocean from cold atmosphere• Arctic mammals (seals, polar bears) hunt, breed, and feed on

the ice

Climatically important Characteristics of sea ice

• Its concentration (fraction of ocean covered by it)• Its extent (area enclosed by the ice edge)• Total area of ice in it’s extent (extent weighted by

concentration)• The area of multi-year ice within total extent• Its thickness• Velocity• Growth and melt rates (affects freshwater flux in

ocean)

• Ice extent, or ice edge position is the only sea ice variable for which observations are available for more than a few decades.

• Expansion or retreat of ice may be amplified by albedo effect.

Measurements

Methods of Measuring Sea Ice Extent

• Passive microwave data from satellites are accurate to 95% but errors of 10% to 20% can be seen during the melt season.

• An algorithm converts the observed radiance to ice concentration.

• It is difficult to distinguish between first year and multiyear ice, but algorithms are improving upon this.

• Aircraft, Ship (19th century) and Coastal observations have also been made with regards to sea ice extent, but data is regional and mainly in the Northern Hemisphere.

Nov 1978 – Dec 2005 annual meanice extent anomalies.

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USS Skate 1959 surfacing -  http://www.csp.navy.mil/asl/ScrapBook/Boats/Skate1959.jpg

USS Hawkbill photo, 1999 -  http://www.usshawkbill.com/scicex3.jpg

Ice Thickness

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The sea ice outflow through the Fram Strait is a major componentof the ice mass balance in the Arctic

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North Atlantic Oscillation

Changes in Glaciers and Ice Caps

Southern Patagonia Ice Cap

Baffin Island Glacier, CanadaTidewater Glacier

Extents of Glaciers and Ice Caps

Earths Ice Mass90% - Antarctica10% - Greenland

<1% - Other*USGS* NSIDC - National Snow and Ice Data Center

Retreat of Glacial Tongues

SH (tropics, New Zealand, Patagonia) NW North America (mainly Canadian Rockies) Atlantic (South Greenland, Iceland, Jan Mayen, Svalbard Scandinavia), European Alps and Asia (Caucasus and central Asia)

Mass balance data is archived and distributed by the World Glacier Monitoring Service (WGMS)

Global Averaged Mean Specific Mass Index

Co5a/i – Cogley, 2005DM05 – Dyurgerov and Meier, 2005O04 – Ohmura, 2004

a – 546X103KM2

b – 785X103 KM2

CELSIAS

Mean Specific Mass Balance vs. Sea Level Rise

Most Significant Climate Change1) Patagonia2) Alaska and Coast Mts3) NW USA and SW Canada

Highest Contributor to Sea Level Rise1) Alaska and Coast Mts2) Arctic3) Asian High Mts

Tropical GlaciersChanges in Surface Area

•Inland is thickening and edges are thinning

•Very noticeable at outlet glaciers

•J represents the Jakobshavn glacier. – Fastest Moving glacier in Greenland. More than doubled in speed from 1997 – 2003 (3.5 mph to 7.8 mph)

Greenland

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Thinning in the southwestThickening in the northeast

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Ice Flow Acceleration• Acceleration in ice flow is important as the faster it is the more ice that moves from land into

the ocean.• Jakobshavn drains 6.5% of Greenland’s ice sheet area. Acceleration doubling (1997 -2003) for

this glacier is very significant. The acceleration of it has increased sea level rise by.06 millimeters per year.

• Also, the rapid movement of ice from land into the sea provides key evidence of newly discovered relationships between ice sheets, sea level rise and climate warming.

• The glacier's sudden speed-up also coincides with very rapid thinning of the glacier, indicating loss of ice of up to 15 meters (49 feet) in thickness per year after 1997. Along with increased rates of ice flow and thinning, the thick ice that extends from the mouth of the glacier into the ocean, called the ice tongue, began retreating in 2000, breaking up almost completely by May 2003.

Mass Balance estimates for Greenland

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Mass Balance estimates for grounded ice in Antarctica

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Assessment of data and techniques by IPCC suggest a mass balance for theGreenland Ice Sheet ranging between

•Growth of 25 Gt per year and Shrinkage of 60 Gt per year from 1961 to 2003.•Shrinkage of 50 and 100 Gt per year from 1993 to 2003•Even higher rate from 2003 to present (derived from only a small amount of estimates and there is a lack of agreement between techniques so data isn’t shown)

X

Y

•Ice balance for east Antarctica ranges from possible growth of 41 Gt per year, and possible loss of 1 Gt per year for the regions monitored.

•Ice balance for west Antarctica ranges from loss of 31 to 57 Gt per year for the region monitored.

•For the regions monitored the combined Ice balance range for Antarctica would be Between a growth of 1Gt per year and a loss of 49Gt per year

•Time period for this is loosely constrained as input data was of varying length and output data was determined primarily in the few years before 2002

Antarctica InSAR measurements

Ice Sheets• Looking at all data and techniques, IPCC assesses Antarctic ice

sheet mass balance ranges from a growth of 50Gt per year to shrinkage of 200 Gt per year from 1993 to 2003.

• IPCC estimates that the mass balance of both ice sheets range from growth of 100 Gt per year and shrinkage of 200 GT per year from 1961 to 2003, but needs to assume accumulation rates, ice flow acceleration rates, and slow time scales affecting central regions of the ice sheets.

• More recent estimates from 1993 to 2003 suggest mass balance ranging from a shrinkage of 0 Gt per year to 300 Gt per year.

Ice Sheets

• Both Antarctica and Greenland ice caps have too few measurements, too many disagreements on measurement techniques, and the existence of systematic error that cannot be estimated accurately for the inclusion of confidence limits and formal error analysis.

Changes in Frozen Ground

Northern HemisphereFrozen Ground

Seasonally Frozen GroundIntermittently Frozen Ground

Thermokarst Lakes (a.k.a thaw lakes)

Recent Trends in Permafrost Temperature

***Permafrost Degradation******Subsea Permafrost***

Changes in the Active Layer

Red Dots - Maximum soil freeze depth stations

Blue Dots – Active layer monitoring stations

Russia 1956 - 1990

Active layer monitoring stations(Mackenzie Delta -

1998)

Current Active Layer Monitoring Sites

Synthesis

FAQ: Is the amount of Snow and Ice on the Earth Decreasing?

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Questions?