Transcript MES_31 Jan Lecture

Spatial and
Temporal
Scale
and Climate
Change
Gangotri Glacier, Uttarkashi District of Garhwal Himalaya
Over the last 25 years, Gangotri glacier has retreated more
than 850 meters, with a recession of 76 meters from 1996 to
1999.
Climate Variability in
Time and Space
• Scale is everything. Some litmus tests:
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Record extent (spatial)  Length of record (temporal)
Grain (spatial)  Resolution of time steps (temporal)
Ubiquity (spatial) vs. coherence (temporal)
Heterogeneity (spatial) vs. nonstationary (temporal)
Process/mechanism scale vs. sampling vs.
conclusions
The tradeoff between record length and
resolution
•
Data from paleomagnetism, magnetic anomalies, paleobiogeography,
and paleoclimatological evidence
http://www.scotese.com/climate.htm
Ice-core proxy records:
Full length with evident multi millennial and
millennial variability in the Vostok core
Higher resolution in the GISP2
record from Greenland.
• Younger
Dryas multimillenial
“event”
• End of the
YD is very
fast
More GISP2
• Inter-annual resolution
possible
• Strength of record is in
groups of decades or
centuries. Letters and pink
bars are cold periods.
From O'Brien, et al., 1995, Science, 270, 1962-1964
More GISP
• Significant variability in
the last 1200 yr.
• Sea-ice extent increase
in 13th and 19th century
and MWP more or less
well resolved
Last 250 yr in ice
• Sulfate and nitrate
concentration increases
evident
• Data smoothed to annual
resolution after 6 or so subannual samples
• Laki, Tambora, and Katmai
eruptions noted form sulfate
signals.
A single event….
to
a
global
propagation
Annual resolution
Quelccaya Ice Cap, Peru
Tree-ring reconstruction of precipitation in northern New Mexico (HG Grissino-Mayer)
Abrupt climate change
• Mechanistic definition
– Transition of the climate
system into a different state
(of temperature, rainfall, and
other aspects) on a time
scale that is faster than the
responsible forcing
•
Impacts-based
definition
– Change of the climate
system that is faster than
the adaptation time of social
and/or ecosystems
• FEEDBACKS: albedo,
precipitation, CO2 (?)
Figure 1. As the Earth climate emerged from the most
recent ice age, the warming that began 15,000 years
ago was interrupted by a cold period known as the
Younger Dryas, which in turn ended with abrupt
warming. Source: Cuffey and Clow (1997) and Alley
(2000).
Different proxies have different
spatial and temporal characteristics
• Handful of ice cores from different
continents; substantial differences in dating
even on cores in close proximity:
Long records, moderate agreement on long
time scales, spatially extensive but poor
coverage
• Handful of tree cores from the same site,
absolutely zero difference in dating
Long records, excellent cross-dating on
annual and centennial time scales, can build
to networks for spatial extent
delta 18O data series
extracted from a Tarawa
coral core. This record is
plotted against
instrumental sea surface
temperature (SST) and
rainfall records and
measurements of the
Southern Oscillation Index
(SOI) in order to observe
how well these corals
have recorded recent
climate variability,
including ENSO events.
Figure courtesy of Dr. Julie Cole, University of Colorado.
Proxies and Climate Variability
• Annual Resolution
with verification
(cross-dating)
– Tree-rings
– Shrub rings
– corals
• Quasi annual
resolution
– Ice cores
– Speleothems
(stalagmites)
– Varved sediments
Snapshots of modern spatial
variability
Spatio-temporal variability
Spatial variability in climate