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October 24, 2012
G 610 – Climate of the Holocene
Presenter:
Erin Dunbar
Assistant:
Jesse Senzer
Defines abrupt climate change
Recent abrupt changes before the
instrumentation timeframe
Threshold models
Urges more effort on the study of abrupt
change
“...occurs when the climate system is forced to
cross some threshold, triggering transition to a
new state at a rate determined by the climate
system itself and faster than the cause.”
-Committee on Abrupt Climate Change, National Research Council
Alley, R.B. et al, Science 2003 Vol. 299, Figure 2
New steady state
Amplifier
Trigger
Persistence
Globalizer
Alley, R.B. et al, Science 2003 Vol. 299, Figure 4
What is the impact of climate change?
Ecological
Economic
What is the impact of our reaction?
Where does the human contribution fit?
Will the changes be like the changes in the
past?
The difficulty of identifying and quantifying all
possible causes of abrupt climate change, and the
lack of predictability near thresholds, imply that
abrupt climate change will always be
accompanied by more uncertainty than will
gradual climate change.
Alley, R.B. et al, Science 2003 Vol. 299
Defines abrupt change as: “… persistent
transition of climate (over subcontinental scale)
that occurs on the timescale of decades.”
Focuses on GCM with coupled oceanic and
atmospheric systems
THC has multiple equilibria
THC circulates most of the poleward heat
transport
Modern mode
Deep water in Nordic sea → Greenland-Scotland
ridge
Glacial mode
Ocean open convection in subpolar NA; brine
rejection
Heinrich mode
Shallow circulation
Loeng, H. et al, CAMEL Climate Change Edu., 9.2.3 of the Arctic Climate Impact Assessment
What is atmospheric
radiocarbon?
Why does Beryllium-10
matter?
What does Figure 1
communicate?
A function of the
production rate of
14C in the upper
atmosphere and
the sizes of and
exchange rates
between the major
carbon reservoirs.
Sediments, Ocean, Terrestrial biosphere
Ruddiman, 2001
Atmospheric radiocarbon offers great promise for identifying past
changes in the globally integrated thermohaline circulation.
Ruddiman, 2001
Can be used to estimate past changes in cosmic
radiation because 10Be is rapidly (1-2yr) removed
from the atmosphere to the ice surface by
precipitation.
Beryllium increases/decreases are linked to
cosmogenic radiation that can help explain
fluctuations in 14C.
Stronger THC =
greater negative
values of 14C
Bolling-Allerod warm
period: 14,700 to
12,700 BP
Younger Dryas:
12,800 to 11,500 BP
Brain, M., 2004, How Carbon-14 Dating Works, How Stuff Works,
http://www.howstuffworks.com/environmental/earth/geology/car
bon-14.htm (October 23, 2012)
Falkowski, P. et al, 2000, The Global Carbon Cycle: A Test of our
Knowledge of Earth as a System, Science, Vol. 290 no. 5490, p. 291296.
Ruddiman, W. F., 2001. Earth's Climate: past and future. W.H.
Freeman & Sons, New York.
Clark, P.U. et al, Nature , 2002 Vol 415, Figure 2
18 time series of climate change
68% variance – captures glacial/interglacial
changes on a 10 kyr timescale
15% variance – captures spatial and temporal
expression of 1 kyr changes between 16 and 12
kya
Negatives over Antarctica & South Atlantic,
positives everywhere else = N.A. climate signal
transmitted everywhere (except in seesaw
locations)
Clark, P.U. et al, Nature , 2002
Vol 415, Figure 3
Abrupt change – 2 ways
Fast forcing
New equilibrium from threshold crossing
Evidence suggests that the THC has two
preferred stable states; flip-flops from one to
another
Models have found three modes of THC in
paleoclimate
Models also indicated these changes were from
freshwater changes
Behavior of climate change can be modeled, but
the cause and effect is not fully understood
Modeling provides ideas for mechanisms of
change, possible future warming, and the
earths’ system responses.
Coupled system models can be enhanced with
geologic data
If heat transport is stopped by the THC being
off, then could there be an offset in heat from
global warming at the northern latitudes