Abrupt Climate Change

October 24, 2012G 610 – Climate of the HolocenePresenter: Erin DunbarAssistant: Jesse Senzer

Abrupt Climate ChangeAlley, R.B. et al

Defines abrupt climate changeRecent abrupt changes before the instrumentation timeframeThreshold modelsUrges more effort on the study of abrupt change

What is abrupt climate 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

Moon Lake, North Dakota

Alley, R.B. et al, Science 2003 Vol. 299, Figure 2

Passing a threshold

Trigger

Amplifier

GlobalizerPersistence

New steady state

THC Steady States

Alley, R.B. et al, Science 2003 Vol. 299, Figure 4

Is the Change Significant?

What is the impact of climate change?EcologicalEconomic

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

The Role of the Thermohaline Circulation in Abrupt Climate ChangeClark, P.U. et al

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 systemsTHC has multiple equilibriaTHC circulates most of the poleward heat transport

North Atlantic Climate

Modern modeDeep water in Nordic sea → Greenland-Scotland ridge

Glacial modeOcean open convection in subpolar NA; brine rejection

Heinrich modeShallow circulation

Loeng, H. et al, CAMEL Climate Change Edu., 9.2.3 of the Arctic Climate Impact Assessment

Agenda

What is atmospheric radiocarbon?Why does Beryllium-10 matter?What does Figure 1 communicate?

Atmospheric RadiocarbonA function of the production rate of 14C in the upper atmosphere and the sizes of and exchange rates between the major carbon reservoirs.

Major carbon reservoirsSediments, Ocean, Terrestrial biosphere

Ruddiman, 2001

Carbon exchange

Atmospheric radiocarbon offers great promise for identifying past changes in the globally integrated thermohaline circulation.

Ruddiman, 2001

Beryllium-10

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.

Figure 1Stronger THC = greater negative values of 14C

Bolling-Allerod warm period: 14,700 to 12,700 BP

Younger Dryas: 12,800 to 11,500 BP

ReferencesBrain, M., 2004, How Carbon-14 Dating Works, How Stuff Works, http://www.howstuffworks.com/environmental/earth/geology/carbon-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. 291-296.

Ruddiman, W. F., 2001. Earth's Climate: past and future. W.H. Freeman & Sons, New York.

Freshwater influx

Clark, P.U. et al, Nature , 2002 Vol 415, Figure 2

Empirical Orthogonal Functions18 time series of climate change68% variance – captures glacial/interglacial changes on a 10 kyr timescale15% variance – captures spatial and temporal expression of 1 kyr changes between 16 and 12 kyaNegatives over Antarctica & South Atlantic, positives everywhere else = N.A. climate signal transmitted everywhere (except in seesaw locations)

Figure 3

Clark, P.U. et al, Nature , 2002 Vol 415, Figure 3

ModelingAbrupt change – 2 ways

Fast forcingNew equilibrium from threshold crossing

Evidence suggests that the THC has two preferred stable states; flip-flops from one to anotherModels have found three modes of THC in paleoclimate

Models also indicated these changes were from freshwater changes

Last thoughts…Behavior of climate change can be modeled, but the cause and effect is not fully understoodModeling provides ideas for mechanisms of change, possible future warming, and the earths’ system responses.Coupled system models can be enhanced with geologic dataIf heat transport is stopped by the THC being off, then could there be an offset in heat from global warming at the northern latitudes