Cryosphere Lecture 6

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The end of the last glacial -
a rapid warming
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Warmer summers early-mid Holocene and recent gradual cooling in
in NW Europe
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European temperature changes based
on pollen Davis and Brewer (2003) QSR 22,1701
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More recent records of millennial scale change (also pollen based) show:
Similar overall patterns of summer temps but with regional variation arising from latitude and influence of precessional changes – greater seasonal change in north - winter temperatures do not track summer changes as previously thought Changes at Bri
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Hints of short-term variability but
hard to separate noise from signal Need to turn to wider range of environmental proxy sources to understand centennial scale change
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Decline in northern mid-high latitude
temperature (at least in summer)
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Big changes from 6000
to present
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The last 1000 years: Is temperature higher now
than at any time in the recent past?
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Little Ice Age and
Medieval warm period
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More recent compilations: some variations but generally support idea of recent temperatures
outside of natural climate variability
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MTWM
Mean temperature of the warmest month
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MTCM
mean temperature of the coldest month
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Anthropogenic forcing:
Greenhouse gases (fossil fuel, deforestation), land cover (albedo), aerosols
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Glacier fluctuations between 6000 years ago and present Long term N hemisphere advance but
short term (recent) retreat
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Glaciers
Major contributors to sea level rise Ice mass loss from glaciers has increased since 1960s
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Loss rates from glaciers outside Greenland and Antarctica
0.7 mm yr-1 SLE 1993-2009 0.83 mm yr-1 SLE 2005-2009
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Permafrost
Permafrost(perenially frozen ground) is overlain by a zone seasonally-thawed ground: the active layer
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Continuous Permafrost
pervasive permafrost beneath the active layer (90- 100% area)
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Discontinuous permafrost
continuity of permafrost broken by through-going talkiks (50-90% area)
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Sporadic permafrost
Isolate blocks of relatively thin permafrost - most common at margins of periglacial environments (10-50% area)
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Active Layer Thickness
ALT
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T at
at 10-20 m depth
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Frozen Ground
Since 1930s Thickness of seasonally frozen ground in NH decreased by 32 cm Since 1970s In NH, southern limit of permafrost moving North Since 1980s Increasing permafrost Temp by up to 2C Active layer thickness increased by up to 90 cm
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Snow Cover
Strong negative correlation between Temp anomaly and Snow Cover Extent (SCE)
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Snow cover continued stats
Between 1967-2012, satellite data show decreases through the year Largest decrease (53%) in June Most stations report decreases, especially in Spring
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Lake & River ice
Contracting Winter ice duration with delays in Autumn Freeze-up proceeding more slowly than advances in Spring break-up Evidence of acceleration in both across the NH
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Sea ice
Between 1970-2012, Arctic sea ice declined at 3.8% per decade Larger losses in Summer and Autumn At the same time, extent of thick multi-year ice in Arctic declined at 13.5% per decade Mean sea ice thickness decreases by 1.3-2.3 m between 1980 -2008
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Ice shelves and Ice tongues
Continuing retreat and collapse of ice shelves along Antarctic Peninsula Progressing thinning of some other ice shelves/ice tongues in Antarctica and Greenland
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Ice sheets
Both Greenland and Antarctic ice shelves lost mass and contributed to sea level changes over the last 20 years Rate of loss and discharge from a number of major outlet glaciers in Antarctica and Greenland increased over this period
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Card 2

Front

Warmer summers early-mid Holocene and recent gradual cooling in

Back

in NW Europe

Card 3

Front

European temperature changes based

Back

Preview of the front of card 3

Card 4

Front

More recent records of millennial scale change (also pollen based) show:

Back

Preview of the front of card 4

Card 5

Front

Hints of short-term variability but

Back

Preview of the front of card 5
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